research on onion

Saunders’ Research Onion: Explained Simply

Peeling the onion, layer by layer (with examples).

By: David Phair (PhD) and Kerryn Warren (PhD) | January 2021

If you’re learning about research skills and methodologies, you may have heard the term “ research onion ”. Specifically, the research onion developed by Saunders et al in 2007 . But what exactly is this elusive onion? In this post, we’ll break Saunders’ research onion down into bite-sized chunks to make it a little more digestible.

Saunders’ (2007) Research Onion – What is it?

At the simplest level, Saunders’ research onion describes the different decisions you’ll need to make when developing a  research methodology   – whether that’s for your dissertation, thesis or any other formal research project. As you work from the outside of the onion inwards , you’ll face a range of choices that progress from high-level and philosophical to tactical and practical in nature. This also mimics the general structure for the methodology chapter .

While Saunders’ research onion is certainly not perfect, it’s a useful tool for thinking holistically about methodology. At a minimum, it helps you understand what decisions you need to make in terms of your research design and methodology.

The layers of Saunders’ research onion

The onion is made up of 6 layers, which you’ll need to peel back one at a time as you develop your research methodology:

• Research philosophy
• Research approach
• Research strategy
• Time horizon
• Techniques & procedures

Onion Layer 1: Research Philosophy

The very first layer of the onion is the research philosophy . But what does that mean? Well, the research philosophy is the foundation of any study as it describes the set of beliefs the research is built upon . Research philosophy can be described from either an  ontological  or  epistemological  point of view. “A what?!”, you ask?

In simple terms,  ontology  is the “what” and “how” of what we know – in other words, what is the nature of reality and what are we really able to know and understand. For example, does reality exist as a single objective thing, or is it different for each person? Think about the simulated reality in the film The Matrix.

Epistemology , on the other hand, is about “how” we can obtain knowledge and come to understand things – in other words, how can we figure out what reality is, and what the limits of this knowledge are. This is a gross oversimplification, but it’s a useful starting point (we’ll cover ontology and epistemology another post).

With that fluffy stuff out the way, let’s look at three of the main research philosophies that operate on different ontological and epistemological assumptions:

• Interpretivism

These certainly aren’t the only research philosophies, but they are very common and provide a good starting point for understanding the spectrum of philosophies.

Research Philosophy 1:  Positivism

Positivist research takes the view that knowledge exists outside of what’s being studied . In other words, what is being studied can only be done so objectively , and it cannot include opinions or personal viewpoints – the researcher doesn’t interpret, they only observe. Positivism states that there is only one reality  and that all meaning is consistent between subjects.

In the positivist’s view, knowledge can only be acquired through empirical research , which is based on measurement and observation. In other words, all knowledge is viewed as a posteriori knowledge – knowledge that is not reliant on human reasoning but instead is gained from research.

For the positivist, knowledge can only be true, false, or meaningless . Basically, if something is not found to be true or false, it no longer holds any ground and is thus dismissed.

Let’s look at an example, based on the question of whether God exists or not. Since positivism takes the stance that knowledge has to be empirically vigorous, the knowledge of whether God exists or not is irrelevant. This topic cannot be proven to be true or false, and thus this knowledge is seen as meaningless.

Kinda harsh, right? Well, that’s the one end of the spectrum – let’s look at the other end.

Research Philosophy 2: Interpretivism

On the other side of the spectrum, interpretivism emphasises the influence that social and cultural factors can have on an individual. This view focuses on  people’s thoughts and ideas , in light of the socio-cultural backdrop. With the interpretivist philosophy, the researcher plays an active role in the study, as it’s necessary to draw a holistic view of the participant and their actions, thoughts and meanings.

Let’s look at an example. If you were studying psychology, you may make use of a case study in your research which investigates an individual with a proposed diagnosis of schizophrenia. The interpretivist view would come into play here as social and cultural factors may influence the outcome of this diagnosis.

Through your research, you may find that the individual originates from India, where schizophrenic symptoms like hallucinations are viewed positively, as they are thought to indicate that the person is a spirit medium. This example illustrates an interpretivist approach since you, as a researcher, would make use of the patient’s point of view, as well as your own interpretation when assessing the case study.

Research Philosophy 3: Pragmatism

Pragmatism highlights the importance of using the best tools possible to investigate phenomena. The main aim of pragmatism is to approach research from a practical point of view , where knowledge is not fixed, but instead is constantly questioned and interpreted. For this reason, pragmatism consists of an element of researcher involvement and subjectivity, specifically when drawing conclusions based on participants’ responses and decisions. In other words, pragmatism is not committed to (or limited by) one specific philosophy.

Let’s look at an example in the form of the trolley problem, which is a set of ethical and psychological thought experiments. In these, participants have to decide on either killing one person to save multiple people or allowing multiple people to die to avoid killing one person. 

This experiment can be altered, including details such as the one person or the group of people being family members or loved ones. The fact that the experiment can be altered to suit the researcher’s needs is an example of pragmatism – in other words, the outcome of the person doing the thought experiment is more important than the philosophical ideas behind the experiment.

To recap, research philosophy is the foundation of any research project and reflects the ontological and epistemological assumptions of the researcher. So, when you’re designing your research methodology , the first thing you need to think about is which philosophy you’ll adopt, given the nature of your research.

Onion Layer 2: Research Approach

Let’s peel off another layer and take a look at the research approach . Your research approach is the broader method you’ll use for your research –  inductive  or  deductive . It’s important to clearly identify your research approach as it will inform the decisions you take in terms of data collection and analysis in your study (we’ll get to that layer soon).

Inductive approaches entail generating theories from research , rather than starting a project with a theory as a foundation.  Deductive approaches, on the other hand, begin with a theory and aim to build on it (or test it) through research.

Sounds a bit fluffy? Let’s look at two examples:

An  inductive approach  could be used in the study of an otherwise unknown isolated community. There is very little knowledge about this community, and therefore, research would have to be conducted to gain information on the community, thus leading to the formation of theories.

On the other hand, a  deductive approach  would be taken when investigating changes in the physical properties of animals over time, as this would likely be rooted in the theory of evolution. In other words, the starting point is a well-established pre-existing body of research.

Closely linked to research approaches are  qualitative and  quantitative  research. Simply put, qualitative research focuses on textual , visual or audio-based data, while quantitative research focuses on numerical data. To learn more about qualitative and quantitative research, check out our dedicated post here .

What’s the relevance of qualitative and quantitative data to research approaches? Well, inductive approaches are usually used within qualitative research, while quantitative research tends to reflect a deductive approach, usually informed by positivist philosophy. The reason for using a deductive approach here is that quantitative research typically begins with theory as a foundation, where progress is made through hypothesis testing. In other words, a wider theory is applied to a particular context, event, or observation to see whether these fit in with the theory, as with our example of evolution above.

So, to recap, the two research approaches are  inductive  and  deductive . To decide on the right approach for your study, you need to assess the type of research you aim to conduct. Ask yourself whether your research will build on something that exists, or whether you’ll be investigating something that cannot necessarily be rooted in previous research. The former suggests a deductive approach while the latter suggests an inductive approach.

Need a helping hand?

Onion Layer 3: Research Strategy

So far, we’ve looked at pretty conceptual and intangible aspects of the onion. Now, it’s time to peel another layer off that onion and get a little more practical – introducing research strategy . This layer of the research onion details how, based on the aims of the study, research can be conducted. Note that outside of the onion, these strategies are referred to as research designs.

There are several strategies  you can take, so let’s have a look at some of them.

• Experimental research
• Action research
• Case study research
• Grounded theory
• Ethnography
• Archival research

Strategy 1: Experimental research

Experimental research involves manipulating one variable (the independent variable ) to observe a change in another variable (the dependent variable ) – in other words, to assess the relationship between variables. The purpose of experimental research is to support, refute or validate a  research hypothesis . This research strategy follows the principles of the  scientific method  and is conducted within a controlled environment or setting (for example, a laboratory).

Experimental research aims to test existing theories rather than create new ones, and as such, is deductive in nature. Experimental research aligns with the positivist research philosophy, as it assumes that knowledge can only be studied objectively and in isolation from external factors such as context or culture.

Let’s look at an example of experimental research. If you had a hypothesis that a certain brand of dog food can raise a dogs’ protein levels, you could make use of experimental research to compare the effects of the specific brand to a “regular” diet. In other words, you could test your hypothesis.

In this example, you would have two groups, where one group consists of dogs with no changes to their diet (this is called  the control group) and the other group consists of dogs being fed the specific brand that you aim to investigate (this is called the experimental/treatment group). You would then test your hypothesis by comparing the protein levels in both groups.

Strategy 2: Action research

Next, we have action research . The simplest way of describing action research is by saying that it involves learning through… wait for it… action. Action research is conducted in practical settings such as a classroom, a hospital, a workspace, etc – as opposed to controlled environments like a lab. Action research helps to inform researchers of problems or weaknesses related to interactions within the real-world . With action research, there’s a strong focus on the participants (the people involved in the issue being studied, which is why it’s sometimes referred to as “participant action research” or PAR.

An example of PAR is a community intervention (for therapy, farming, education, whatever). The researcher comes with an idea and it is implemented with the help of the community (i.e. the participants). The findings are then discussed with the community to see how to better the intervention. The process is repeated until the intervention works just right for the community. In this way, a practical solution is given to a problem and it is generated by the combination of researcher and community (participant) feedback.

This kind of research is generally applied in the social sciences , specifically in professions where individuals aim to improve on themselves and the work that they are doing. Action research is most commonly adopted in qualitative studies and is rarely seen in quantitative studies. This is because, as you can see in the above examples, action research makes use of language and interactions rather than statistics and numbers.

Strategy 3: Case study research

A case study is a detailed, in-depth study of a single subject – for example, a person, a group or an institution, or an event, phenomenon or issue. In this type of research, the subject is analysed to gain an in-depth understanding of issues in a real-life setting. The objective here is to gain an in-depth understanding within the context of the study – not (necessarily) to generalise the findings.

It is vital that, when conducting case study research, you take the social context and culture into account, which means that this type of research is (more often than not) qualitative in nature and tends to be inductive. Also, since the researcher’s assumptions and understanding play a role in case study research, it is typically informed by an interpretivist philosophy.

For example, a study on political views of a specific group of people needs to take into account the current political situation within a country and factors that could contribute towards participants taking a certain view.

Strategy 4: Grounded theory

Next up, grounded theory. Grounded theory is all about “letting the data speak for itself”. In other words, in grounded theory, you let the data inform the development of a new theory, model or framework. True to the name, the theory you develop is “ grounded ” in the data. Ground theory is therefore very useful for research into issues that are completely new or under-researched.

Grounded theory research is typically qualitative (although it can also use quantitative data) and takes an inductive approach. Typically, this form of research involves identifying commonalities between sets of data, and results are then drawn from completed research without the aim of fitting the findings in with a pre-existing theory or framework.

For example, if you were to study the mythology of an unknown culture through artefacts, you’d enter your research without any hypotheses or theories, and rather work from the knowledge you gain from your study to develop these.

Strategy 5: Ethnography

Ethnography involves observing people in their natural environments and drawing meaning from their cultural interactions. The objective with ethnography is to capture the subjective experiences of participants, to see the world through their eyes. Creswell (2013) says it best: “Ethnographers study the meaning of the behaviour, the language, and the interaction among members of the culture-sharing group.”

For example, if you were interested in studying interactions on a mental health discussion board, you could use ethnography to analyse interactions and draw an understanding of the participants’ subjective experiences.

For example, if you wanted to explore the behaviour, language, and beliefs of an isolated Amazonian tribe, ethnography could allow you to develop a complex, complete description of the social behaviours of the group by immersing yourself into the community, rather than just observing from the outside.  

Given the nature of ethnography, it generally reflects an interpretivist research philosophy and involves an inductive , qualitative research approach. However, there are exceptions to this – for example, quantitative ethnography as proposed by David Shafer.

Strategy 6: Archival research

Last but not least is archival research. An archival research strategy draws from materials that already exist, and meaning is then established through a review of this existing data. This method is particularly well-suited to historical research and can make use of materials such as manuscripts and records.

For example, if you were interested in people’s beliefs about so-called supernatural phenomena in the medieval period, you could consult manuscripts and records from the time, and use those as your core data set.

Onion Layer 4: Choices

The next layer of the research onion is simply called “choices” – they could have been a little more specific, right? In any case, this layer is simply about deciding how many data types (qualitative or quantitative) you’ll use in your research. There are three options – mono , mixed , and multi-method .

Let’s take a look at them.

Choosing to use a  mono method  means that you’ll only make use of one data type – either qualitative or quantitative. For example, if you were to conduct a study investigating a community’s opinions on a specific pizza restaurant, you could make use of a qualitative approach only, so that you can analyse participants’ views and opinions of the restaurant.

If you were to make use of both quantitative and qualitative data, you’d be taking a  mixed-methods approach. Keeping with the previous example, you may also want to assess how many people in a community eat specific types of pizza. For this, you could make use of a survey to collect quantitative data and then analyse the results statistically, producing quantitative results in addition to your qualitative ones.

Lastly, there’s  multi-method . With a multi-method approach, you’d make use of a wider range of approaches, with more than just a one quantitative and one qualitative approach. For example, if you conduct a study looking at archives from a specific culture, you could make use of two qualitative methods (such as thematic analysis and content analysis ), and then additionally make use of quantitative methods to analyse numerical data.

As with all the layers of the research onion, the right choice here depends on the nature of your research, as well as your research aims and objectives . There’s also the practical consideration of viability – in other words, what kind of data will you be able to access, given your constraints.

Onion Layer 5: Time horizon

What’s that far in the distance? It’s the time horizon. But what exactly is it? Thankfully, this one’s pretty straightforward. The time horizon simply describes how many points in time you plan to collect your data at . Two options exist – the  cross-sectional  and  longitudinal  time horizon.

Imagine that you’re wasting time on social media and think, “Ooh! I want to study the language of memes and how this language evolves over time”. For this study, you’d need to collect data over multiple points in time – perhaps over a few weeks, months, or even years. Therefore, you’d make use of a  longitudinal time horizon. This option is highly beneficial when studying changes and progressions over time.

If instead, you wanted to study the language used in memes at a certain point in time (for example, in 2020), you’d make use of a  cross-sectional  time horizon. This is where data is collected at one point in time, so you wouldn’t be gathering data to see how language changes, but rather what language exists at a snapshot point in time. The type of data collected could be qualitative, quantitative or a mix of both, as the focus is on the time of collection, not the data type.

As with all the other choices, the nature of your research and your research aims and objectives are the key determining factors when deciding on the time horizon. You’ll also need to consider practical constraints , such as the amount of time you have available to complete your research (especially in the case of a dissertation or thesis).

Onion Layer 6: Techniques and Procedures

Finally, we reach the centre of the onion – this is where you get down to the real practicalities of your research to make choices regarding specific techniques and procedures .

Specifically, this is where you’ll:

• Decide on what data you’ll collect and what data collection methods you’ll use (for example, will you use a survey? Or perhaps one-on-one interviews?)
• Decide how you’ll go about sampling the population (for example, snowball sampling, random sampling, convenience sampling, etc).
• Determine the type of data analysis you’ll use to answer your research questions (such as content analysis or a statistical analysis like correlation).
• Set up the materials you’ll be using for your study (such as writing up questions for a survey or interview)

What’s important to note here is that these techniques and procedures need to align with all the other layers of the research onion – i.e., research philosophy, research approaches, research strategy, choices, and time horizon.

For example, you if you’re adopting a deductive, quantitative research approach, it’s unlikely that you’ll use interviews to collect your data, as you’ll want high-volume, numerical data (which surveys are far better suited to). So, you need to ensure that the decisions at each layer of your onion align with the rest, and most importantly, that they align with your research aims and objectives.

Let’s Recap: Research Onion 101

The research onion details the many interrelated choices you’ll need to make when you’re crafting your research methodology. These include:

• Research philosophy – the set of beliefs your research is based on (positivism, interpretivism, pragmatism)
• Research approaches – the broader method you’ll use (inductive, deductive, qualitative and quantitative)
• Research strategies – how you’ll conduct the research (e.g., experimental, action, case study, etc.)
• Choices – how many methods you’ll use (mono method, mixed-method or multi-method)
• Time horizons – the number of points in time at which you’ll collect your data (cross-sectional or longitudinal)
• Techniques and procedures (data collection methods, data analysis techniques, sampling strategies, etc.)

Psst... there’s more!

This post was based on one of our popular Research Bootcamps . If you're working on a research project, you'll definitely want to check this out ...

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59 Comments

This is good

Wow this was sooo helpful. I don’t feel so blank about my research anymore. With this information I can conquer my research. Going ‘write’ into it. Get it write not right hahahaha

I am doing research with Bolton University so i would like to empower myself.

Really thoughtful presentation and preparation. I learnt too much to teach my students in a very simple and understandable way

Very useful, thank you.

You’re most welcome. Good luck with your research!

thanks alot for your brief and brilliant notes

I am a Student at Malawi Institute of Management, pursuing a Masters’ degree in Business Administration. I find this to be very helpful

Extremely useful, well explained. Thank you so much

I would like to download this file… I can’t find the attachment file. Thanks

Thank you so much for explaining it in the most simple and precise manner!

Very thoughtful and well expained, thanks.

This is good for upgrade my research knowledge

I have enjoying your videos on YouTube, they are very educative and useful. I have learned a lot. Thanks

Thank you this has really helped me with writing my dissertation methodology !

Thanks so much for this piece. Just to be clear, which layer do interviews fit in?

well explained i found it to be very engaging. now i’m going to pass my research methods course. thank you.

Thank you so much this has really helped as I can’t get this insight from uni due to covid

well explained with more clarity!

this is an excellent piece i find it super helpful

Beautiful, thank you!

Beautiful and helpful. Thank you!

This is well done!

A complex but useful approach to research simplified! I would like to learn more from the team.

A very simplified version of a complex topic. I found it really helpful. I would like to know if this publication can be cited for academic research. Thank you

You’re welcome to cite this page, but it would be better to cite the original work of Saunders.

Thirteen odd years since my MSc in HRM & HRD at UoL. I’d like to say thank you for the effort to produce such an insightful discussion of a rather complex topic.

I am a PhD in Media Studies student. I found this enormously helpful when stringing together the methodology chapter, especially the research philosophy section.

Hello there. Thank you for summarising the work on the onion. A more recent version of the onion (Saunders et al., 2019) refers to ‘methodological choices’ rather than choices. This can be downloaded, along with the chapter dealing with research philosophies at: https://www.researchgate.net/publication/330760964_Research_Methods_for_Business_Students_Chapter_4_Understanding_research_philosophy_and_approaches_to_theory_development or https://www.academia.edu/42304065/Research_Methods_for_Business_Students_Chapter_4_Understanding_research_philosophy_and_approaches_to_theory_development_8th_edition

Thank you Mark Saunders. Your work is very insightful

Thank you for the update and additional reading Mark, very helpful indeed.

THROUGHLY AND SIMPLY BRIEFED TO MAKE SENSE AND A CLEAR INSIGHT. THANK YOU, VERY MUCH.

Thank you for the sharing the recent version of the Onion!

I want to keep it in my reference of my assignment. May I??

Great summary, thank you taking the time to put this together. I’m sure it’s been a big help to lots of people. It definitely was to me.

I love the analysis… some people do not recognize qualitative or quantitative as an approach but rather have inductive, abductive, and deductive.

This has been helpful in the understanding of research . Thank you for this valuable information.

Great summary. Well explained. Thank you, guys.

This makes my fears on methodology go away. I confidently look forward to working on my methodology now. Thank you so much I ma doing a PhD with UNIMA, School of Education

simple and clear

Simple guide to crafting a research methodology. Quite impactful. Thank you

Thank you for this, this makes things very clear. Now I’m off to conquer my research proposal. Thanks again.

Thank you for this very informative and valuable information. What would the best approach be to take if you are using secondary data to form a qualitative study and relying on industry reports and peer journals to distinguish what factors influence the use of say cryptocurrency ?

Thanks for providing the whole idea/knowledge in the simplest way with essential factors which made my entire research process more efficient as well as valuable.

what is about research design such as descriptive, causal-comparative, correlation, developmental where these fall in the research onion?

This is very helpful. Thank you for this wonderful piece. However, it would be nicer to have References to the knowledge provided here. My suggestion

This material is very important for researchers, particularly for PhD scholars to conduct further study.

This was insightful. Thank you for the knowledge.

Thank you for the wonderful knowledge !Easy to understand and grasp.

thanks very much very simple. will need a coach

Hi this is a great article giving much help to my research. I just wanted to mention here that the example where you mentioned that ” schizophrenic symptoms like hallucinations are viewed positively, as they are thought to indicate the person is a spirit medium” is completely false as those are different cases and a bit out of context here. We are medically and psychologically well versed and obviously understand the difference between the two. As much as I am grateful to this article I would like to suggest you to give proper examples.

Thank you very much, sincerely I appreciate your efforts, it is insightful information. Once again I’m grateful .

In short, a complete insight of and for writing research methodology.

This information was very helpful, I was having difficulties in writing my methodology now I can say I have the full knowledge to write a more informative research methodology.

Thank you so much for this amazing explanation. As a person who hasn’t ever done a research project, this video helped me to clear my doubts and approach my research in a clear and concise manner. Great work

very well explained , after going through this there is no need any material to study . a very concise and to the point.

I have one small query. If I choose mixed -methods (quantitative and qualitative techniques), Then, my research Philosophy will also change to both Positivists and Interpretivist. Isn’t?

well explained and thank you

Thanks for this presentation. Quite simple and easy to understand, and to teach others.

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National Onion Association

Onion Health Research

Onions not only provide flavor, they also provide important nutrients and health-promoting phytochemicals. Plenty of onion health research provides strong evidence of its nutritional value.

Here are some highlights:

• High in Vitamin C, onions are a good source of dietary fiber, and folic acid.
• They also contain calcium, iron, and have a high protein quality (ratio of mg amino acid/gram protein).
• Onions are low in sodium and contain no fat.
• Onions contain quercetin, a flavonoid (one category of antioxidant compounds).
• Onions contain organosulfur compounds that may offer unique health benefits.

Antioxidants are compounds that help delay or slow the oxidative damage to cells and tissue of the body. Studies have indicated that quercetin helps to eliminate free radicals in the body, to inhibit low-density lipoprotein oxidation (an important reaction in the atherosclerosis and coronary heart disease), to protect and regenerate vitamin E (a powerful antioxidant), and to inactivate the harmful effects of chelate metal ions.

Want to try some great onion recipes? Go here. 

How to get more quercetin in your diet:.

Studies at Wageningen Agricultural University, the Netherlands, showed that the absorption of quercetin from onions is twice that from tea and more than three times that from apples.

Based on studies conducted at The Queen’s University at Belfast, Ireland and Wageningen Agricultural University, the content of quercetin in onions is estimated to be between 22.40 mg and 51.82 mg per medium-sized onion (100 grams). Further research at the Agricultural University of Wageningen showed that daily consumption of onions may result in increased accumulation of quercetin in the blood.

Several studies have been conducted to evaluate the effects quercetin from onions has on the body. Many have shown that consumption of onions may be beneficial for reduced risk of certain diseases.

This 2015 study , published in the British Journal of Nutrition, concluded that supplementation with 162 mg/d quercetin from onion skin extract lowers ambulatory blood pressure in patients with hypertension, suggesting a cardioprotective effect of quercetin.

Other studies suggest that the increased quercetin accumulation from eating onions translates into significant antioxidant benefit. The results of this study indicate that quercetin metabolites present in systemic circulation after quercetin consumption may act as potent antioxidants and anti-inflammatory agents and should without doubt be considered when defining overall biological activity of quercetin-rich food in vitro and in vivo.

This study found that onion had an anti-diabetic effect in animals and a blood sugar lowering effect in humans.  

This study , published in April 2020 in the American Journal of Clinical Nutrition , found that a diet rich in flavonoids — commonly found in onions — can reduce the risk of developing Alzheimer’s Disease and related dementias.

Onions – Phytochemical and Health Research

Click here to view or download the guide (PDF)

Consumption of onions may prevent gastric ulcers by scavenging free radicals and by preventing growth of the ulcer-forming microorganism, Heliobacter pylori .

• University of Wisconsin-Madison researchers found that the more pungent onions exhibit strong anti-platelet activity. Platelet aggregation is associated with atherosclerosis, cardiovascular disease, heart attack and stroke.

A European study in 2006 looked at the extent to which onion consumption and specific onion compounds affect the in vivo aggregation of blood platelets. This study states that a diet rich in quercetin from onions suggests that “those who preferentially consume high amounts of quercetin-containing foods have a reduced risk of thrombosis and cardiovascular disease risk.”

A study at the University of Bern in Switzerland showed that consumption of one gram dry onion per day for four weeks increased bone mineral content in rats by more than 17% and mineral density by more than 13% compared to animals fed a control diet. This data suggests onion consumption has the potential to decrease the incidence of osteoporosis.

Effects on cancers

Several studies have shown quercetin to have beneficial effects against many diseases and disorders including cataracts, cardiovascular disease as well as cancer of the breast, colon, ovarian, gastric, lung, and bladder.

A 2019 study in China  found that regular consumption of allium vegetables (of which the onion is a member) could reduce the incidence of colorectal cancer by as much as 79 percent. The study recommended consumption of 35 pounds of alliums per year. (That’s slightly higher than the average American consumption of onions, which sat at 21.9 pounds per person in 2017.

A study published in August 2019 showed a clear link between the amount of onions and garlic consumption and the reduced risk of breast cancer.

In addition to quercetin, onions contain organosulfur compounds, including disulfides, trisulfides, cepaene and vinyl dithiins. These compounds have a variety of health-functional properties, including anticancer and antimicrobial activities.

More about onion nutrition here

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Recent Advances in Bioactive Compounds, Health Functions, and Safety Concerns of Onion ( Allium cepa L.)

Xin-xin zhao.

1 Institute of Urban Agriculture, Chinese Academy of Agricultural Sciences, Chengdu, China

2 Chengdu National Agricultural Science and Technology Center, Chengdu, China

Fang-Jun Lin

3 Burnett School of Biomedical Sciences, University of Central Florida, Orlando, FL, United States

4 Guangdong Provincial Key Laboratory of Food, Nutrition, and Health, Department of Nutrition, School of Public Health, Sun Yat-sen University, Guangzhou, China

Ding-Tao Wu

5 Key Laboratory of Coarse Cereal Processing (Ministry of Agriculture and Rural Affairs), Sichuan Engineering and Technology Research Center of Coarse Cereal Industralization, Chengdu University, Chengdu, China

Bao-He Miao

Ren-you gan.

Onion ( Allium cepa L.) is a common vegetable, widely consumed all over the world. Onion contains diverse phytochemicals, including organosulfur compounds, phenolic compounds, polysaccharides, and saponins. The phenolic and sulfur-containing compounds, including onionin A, cysteine sulfoxides, quercetin, and quercetin glucosides, are the major bioactive constituents of onion. Accumulated studies have revealed that onion and its bioactive compounds possess various health functions, such as antioxidant, antimicrobial, anti-inflammatory, anti-obesity, anti-diabetic, anticancer, cardiovascular protective, neuroprotective, hepatorenal protective, respiratory protective, digestive system protective, reproductive protective, and immunomodulatory properties. Herein, the main bioactive compounds in onion are summarized, followed by intensively discussing its major health functions as well as relevant molecular mechanisms. Moreover, the potential safety concerns about onion contamination and the ways to mitigate these issues are also discussed. We hope that this paper can attract broader attention to onion and its bioactive compounds, which are promising ingredients in the development of functional foods and nutraceuticals for preventing and managing certain chronic diseases.

Introduction

Onion ( Allium cepa L.) is widely cultivated and consumed around the world ( 1 ). The common onion varieties with three different colors, including red, yellow, and white, are normally available in the food market. As a food item, onion is usually served as a vegetable ingredient in warm dishes by cooking, like baking, boiling, braising, grilling, frying, roasting, sautéing, or steaming. It can also be eaten raw in salads, made into juice, pickled in vinegar, or used as a spice. As an herbal medicine, onion is recommended to relieve or prevent several common diseases, such as atherosclerosis, asthma, bronchitis, and coughs. The health benefits of onion are mainly attributed to its diverse bioactive constituents, such as organosulfur compounds, phenolic compounds, polysaccharides, and saponins ( 2 , 3 ). Recently, accumulated studies demonstrated the remarkable health functions of onion and its bioactive compounds, including antioxidant ( 4 ), antimicrobial ( 5 ), anti-inflammatory ( 6 ), anti-obesity ( 7 ), anti-diabetic ( 8 ), anticancer ( 9 ), cardiovascular protective ( 10 ), neuroprotective ( 11 ), hepatorenal protective ( 12 ), respiratory protective ( 13 ), digestive system protective ( 14 ), reproductive protective ( 15 ), and immunomodulatory properties ( 16 ). Generally speaking, onion consumption is quite safe for the consumers. However, several potential health concerns should not be ignored, such as pesticide residue ( 17 ), heavy metal-enrichment ( 18 , 19 ), microbial contamination ( 20 , 21 ), and nitrate accumulation ( 22 ).

Although the bioactive compounds and certain bioactivities of onion have been discussed in recent reviews ( 3 , 23 , 24 ), this review can provide an updated and more comprehensive understanding about the diverse health functions and safety concerns of onion. The literature summarized in this review was mainly collected from Web of Science Core Collection, PubMed, and Scopus databases from 2016 to 2021, with a focus on the bioactive compounds and health functions of onion, with special attention paid to the relevant molecular mechanisms ( Figure 1 ). The potential safety concerns of onion and the strategies to mitigate these health risks are also discussed. It is expected to attract more attention to the health benefits of onion and its consumption and application in the prevention and management of chronic diseases.

Bioactive compounds and health functions of onion.

Bioactive Compounds in Onion

Onion is rich in a variety of phytochemicals with beneficial functional, including organosulfur compounds ( 25 , 26 ), phenolic compounds ( 27 – 29 ), polysaccharides ( 30 ), and saponins ( 31 , 32 ). The major bioactive compounds of onion are sulfur-containing compounds, such as onionin A and cysteine sulfoxides, as well as the phenolic compounds, such as rutin, quercetin, and quercetin glucosides ( Figure 2 ). It is different for the contents of bioactive compounds among different onion varieties ( 5 ). Red onion had the highest contents of anthocyanins and flavonols, followed by the yellow onion, but the white onion contained the lowest amount ( 33 ). Besides, the major compounds varied in different layers of onion ( 34 ). Quercetin was the major compound in the skin of red onion, while quercetin-4-glucoside was the main compound in its bulb ( 35 ).

The chemical structures of the main organosulfur and phenolic compounds in onion.

Processing can change the bioaccessibility and content of bioactive compounds in onion. The bioaccessibility of total flavonols in onion was not affected by high-pressure processing, but the onion matrix could improve the bioaccessibility of its flavonol ( 36 ). It has been found that onion skin quercetin aglycone was more bioavailable than pure quercetin dihydrate in humans ( 37 ). The quercetin content was not significantly changed by sautéing ( 38 ), but the content and bioaccessibility of phenolic compounds, especially quercetin-derivatives, were found increased by cooking, such as baking, grilling, and frying ( 39 ). Besides, the contents of the cysteine sulfoxides, including cycloalliin, isoalliin, methiin, and propiin, were changed differently in onion by heat processing, depending on the cooking methods ( 40 ). For instance, their contents were decreased during boiling, but increased during frying, microwaving, and steaming. Furthermore, the flavonoid content was decreased during the processing of black onion, while the contents of isoalliin and fructose were significantly increased ( 41 ).

Health Functions of Onion

Many plant-based foods, such as garlic ( 42 ), ginger ( 43 ), sweet tea ( 44 ), dark tea ( 45 ), germinated edible seeds and sprouts ( 46 ), as well as their bioactive compounds, including resveratrol ( 47 ), curcumin ( 48 ), rutin ( 49 ), quercetin ( 50 ), citrus flavonoids ( 51 ), and spice essential oils ( 52 ) have been demonstrated to possess a variety of health functions. As a traditional and popular food, onion has also been reported with multiple health functions based on in vitro, in vivo , and human studies ( Table 1 ). In the following part, the main health functions and related molecular mechanisms of onion and its bioactive compounds are summarized and discussed in detail.

The health functions and potential mechanisms of onion.

Antioxidant Activity

Onion is a good source of natural antioxidants ( 128 ). Many studies have been carried out to evaluate the antioxidant activities of onion, and found that onion exhibits strong antioxidant properties by using a series of in vitro assays, including 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 1,1-diphenyl-2-picrilhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), lipid peroxidation, oxygen radical absorbance capacity (ORAC), total antioxidant capacity (TAC), and trolox equivalent antioxidant capacity (TEAC) assays.

Many factors were reported to influence the antioxidant activity of onion, such as the genetic background, horticultural techniques, storage conditions, distinct parts, extraction methods, and processing technologies ( Figure 3 ). Several studies reported that the antioxidant activity varied among different onion cultivars or varieties ( 5 , 129 – 132 ), probably related to their genetic background ( 133 ). In addition, organic cultivation practices ( 28 , 134 ), sulfur bentonite-organic-based fertilizers ( 135 ), and mycorrhizal fungi ( 136 ) were reported to improve the content of bioactive compounds with antioxidant activities in onions. The content of phenolics in the onion bulb and its antioxidant property were increased with the application of mycorrhizal inocula, humic acids, and elevated atmospheric CO 2 ( 137 ). Planting time and density were also found to influence the antioxidant components of onion seeds ( 138 ). Besides, stored atmosphere conditions could affect the quality and bioaccessibility of total phenolics and antioxidant activity of the floral stem of the second-year onion resprout ( 139 ). Washing the fresh-cut onions with a combination of nisin and citric acid was reported to increase the total phenolic and flavonoid contents, and antioxidant capacity during storage ( 140 ). Sprouting of onion also increased its antioxidant activity, and contents of total phenolics and flavonoids ( 141 , 142 ). Furthermore, the antioxidant activities in distinct parts of red onion, such as the dry skin and edible portion, were segregated based on the principal component analysis, probably due to the former rich in quercetin while the latter rich in quercetin-4-glucoside ( 35 ). The influences of food processing on antioxidant capacities of onions were investigated as well, including drying ( 143 , 144 ), freezing ( 145 ), heating ( 41 , 145 ), sautéing ( 38 ), and high-pressure processing ( 36 ). For instance, heating and freezing were found to reduce antioxidant activity of onion ( 145 ), while sautéing did not significantly change it ( 38 ).

The main influence factors for antioxidant activity of onion.

Onion also exhibits antioxidant activity in cell and animal models. The expression of antioxidant enzymes, including catalase (CAT), NAD(P)H quinone dehydrogenase 1 (NQO1), and hemeoxygenase-1 (HO-1), was upregulated by onion extract in N27-A cells ( 6 ). In addition, several studies demonstrated that onion treatment could improve the antioxidant status of animals. Onion was effective for protection against oxidative stress by enhancing the activity of antioxidant enzymes, such as superoxide dismutase (SOD), CAT, and glutathione peroxidase (GPx), in hypercholesterolemic rats ( 10 ). The oxidative stress in the liver and kidney was ameliorated by pre-treatment with red onion peel extract in carbon tetrachloride-challenged rats ( 12 ). Onion fortified feed ameliorated the liver and kidney oxidative damages in rats administered with potassium bromate ( 54 ). Dietary addition of onion extract and combining onion peel powder with pawpaw seed were found to increase antioxidant enzyme activity in broiler chicks ( 55 ) and African catfish ( 56 ), respectively. Furthermore, a clinical trial revealed that drinking onion juice (100 mL) for 8 weeks could reduce total free radicals and superoxide anions levels, while elevate the glutathione content and total antioxidant capacity in healthy subjects ( 57 ).

Overall, onion exhibits strong antioxidant effects, and many factors could affect the antioxidant capability of onion. Although the antioxidant activity of onion has been extensively investigated, the related antioxidant molecular mechanism has been much less explored, which should be further clarified in the future.

Antimicrobial Activity

Onion extracts and their derived bioactive compounds, such as thiosulfinate compounds, phenolic compounds, polysaccharides, and essential oils, have been reported to possess potent antibacterial properties ( 5 , 30 , 58 , 146 ), antifungal activities ( 64 , 66 ), and antiviral effects ( 147 ). Different drying methods, such as microwave drying, air drying, and freeze drying, were performed to evaluate the influence of drying processes on its antimicrobial activity, of which freeze-dried onion bulbs showed a stronger antimicrobial property ( 148 ).

Onion fiber-based composite materials combining with isolated flavonoids from onion skins were reported to exhibit certain antibacterial activity against Staphylococcus aureus and Escherichia coli ( 149 ). Moreover, it was demonstrated that gold nanoparticles ( 150 ), silver nanoparticles ( 151 ), graphene ( 60 ), and polymeric films ( 63 ) containing onion extracts exhibited excellent antibacterial properties against both gram-positive and gram-negative bacteria. Quorum sensing is very important for the coordination of bacterial virulence during infection. One result found that onion organic extracts and quercetin had interference on quorum sensing-regulated production of violacein and swarming motility in Pseudomonas aeruginosa and Serratia marcescens , of which quercetin aglycone reduced violacein production while quercetin aglycone and quercetin 3-β-D-glucoside inhibited bacterial motility ( 152 ). It is surprising that the biofilm formation, another crucial factor for antimicrobial resistance controlled by quorum sensing system, was not affected by the onion extracts or quercetin ( 152 ). In other studies, quorum sensing-mediated virulence factors in pathogens, such as biofilm formation, were found to be inhibited by the β-sitosterol derived compounds from onion husk extract ( 61 ) and quercetin 4′- O -β-D glucopyranoside from onion peel extract ( 153 ). Besides, onion essential oil was revealed to possess anti-biofilm activity against Listeria monocytogenes as well ( 154 ).

Onion essential oil was reported to showed fungicidal or inhibitory effects on the growth of fungal species isolated from food, including Aspergillus, Fusarium , and Penicillium species ( 64 ). Biosynthesis of silver nanoparticles using onion endophytic bacterium Bacillus endophyticus showed an effective antifungal effect against rice blast pathogen Magnaporthe oryzae with abnormal mycelia morphology and 88% inhibition rate of mycelium diameter ( 65 ). Besides, the ethanol extract of red onion was effective in preventing tinea pedis caused by the fungal infection of Trichophyton rubrum ( 66 ).

Therefore, onion has been demonstrated to inhibit the growth of microbes, showing great potential to be used as a natural preservative in the food industry, such as maintaining meat quality during refrigerated storage ( 155 ).

Anti-inflammatory Activity

Onion also exhibited anti-inflammatory property, showing protective effects against inflammation-related diseases, such as neuroinflammation ( 6 , 156 ), allergic inflammation ( 13 ), lung inflammation ( 68 ), colitis ( 14 , 69 ), and paw edema ( 70 ). The anti-neuroinflammatory activities of onion extract were investigated in lipopolysaccharide (LPS)-induced BV-2 microglial cells. The methanol extract of onion could reduce the nitric oxide (NO) release by down-regulating the mRNA and protein levels of cyclooxygenase-2 (COX2) and inducible NO synthase (iNOS), and attenuate the elevation of proinflammatory cytokines, including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 ( 6 ). Onion-derived nanoparticles and flavonoids from onion peels were reported to prevent the LPS-stimulated NO production in RAW264 cells ( 67 ) and BV-2 cells ( 156 ), respectively. Besides, the extract of onion bulb alleviated house dust mite-induced perivascular and peribronchial inflammation by inhibiting the epidermal growth factor receptor (EGFR)/extracellular signal-regulated kinase (ERK1/2)/protein kinase B (PKB/AKT) signaling pathway ( 13 ). Moreover, onion extract significantly reduced lung inflammatory cells, including monocyte, neutrophil, and eosinophil in asthmatic rats ( 68 ). Onion bulb extract was reported to both prevent and reverse colitis by regulating some pro-inflammatory signaling pathways, such as mechanistic target of rapamycin (mTOR), mitogen-activated protein kinase family (MAPK), cyclooxygenase-2 (COX-2), and tissue-inhibitors of metalloproteinases (TIMP), as well as several molecules involved in the apoptotic pathway, such as caspase-3, caspase-8, cytochrome c, B-cell lymphoma-extra-large (Bcl-XL), and Bcl-2 in mice ( 14 , 69 ). In addition, intraperitoneally injection of onion aqueous extract dose dependently reduced Carrageenan-induced paw edema in rats ( 70 ). Therefore, onion can be a good food resource with anti-inflammatory activity for the prevention of inflammation-related diseases.

Anti-obesity Activity

Promoting the browning of white adipose tissue is a promising strategy for the prevention of obesity. Quercetin from onion peel has been demonstrated to have browning effects in 3T3-L1 adipocytes and the white adipose tissue of mice ( 157 ). Several animal studies and clinical trials have reported that onion is effective in the prevention and management of obesity. Onion peel extract inhibited lipid accumulation in 3T3-L1 cells and reduced body weight in high-fat diet-fed mice via down-regulating the expression of lipogenesis-related genes ( 71 ). Red onion extract or quercetin supplementation could ameliorate obesity and insulin resistance in mice fed with a high-fat diet ( 72 ). Oral administration of onion oil prevented the body weight gain of rats triggered by high-fat diets ( 73 ). Moreover, dietary supplementation of onion peel extract was found to reduce the body weight, body fat mass, and percentage of body fat in overweight and obese Korean subjects ( 7 , 76 ). Consumption of steamed onion resulted in a positive change of metabolic parameters, lowering the levels of triglycerides and C-peptide, and reduced the percentage of body fat, total body fat, visceral fat, and subcutaneous fat in overweight people ( 75 ). In addition, daily intake of onion powder improved the visceral fat area in healthy Japanese subjects with a high-density lipoprotein cholesterol level between 40 and 74 mg/dL ( 74 ). Generally, onion and its bioactive compounds have potential application in the management of obesity.

Anti-diabetic Activity

Increasing evidence from in vitro and in vivo studies have demonstrated that onions can not only ameliorate diabetes, but also treat different diabetic complications ( Figure 4 ). Several studies indicate that onion exhibits antidiabetic potential in vitro . The extracts of onion skin or onion solid waste showed a remarkable inhibitory activity toward α-glucosidase and α-amylase, and the enzyme inhibitory activity was in a dose-dependent manner ( 158 , 159 ). Besides, onion-based green synthesized silver nanoparticles were found to exhibit excellent α-glucosidase and α-amylase inhibitory activities ( 8 ). In another study, onion fiber concentrates were revealed to reduce starch digestibility and glucose production rate by suppressing α-amylase activity ( 160 ).

The effects of onion in diabetes and diabetic complications.

Onion also exhibits antidiabetic potential in vivo . The heat-processed onion extract was found to have a high content of Amadori rearrangement compounds, which reduced the post-prandial carbohydrate absorption and blood glucose levels by inhibiting intestinal sucrase activity in rats fed with sucrose or starch meals ( 85 ). Moreover, hyperglycemia and its associated metabolic disorders were reported to be ameliorated by dietary supplementation with fenugreek seeds and onion in diabetic rats ( 78 ). Hyperglycemia-induced osmotic and oxidative stress is a primary factor in the progression of diabetic complications. It has been reported that intake of fenugreek seeds and onion could also reduce oxidative stress ( 79 ), ameliorate eye lens abnormalities ( 82 ), alleviate cardiac damage ( 80 ), attenuate diabetic nephropathy ( 81 , 86 ), and counter the deformity and fragility of erythrocytes ( 83 ) in STZ-induced diabetic rats. Tamtaji et al. ( 105 ) reported that the ethanolic extract of onion had a protective effect on learning and memory deficits in diabetic rats. Furthermore, the anti-diabetic activities of the inedible parts of onion, including skin, seeds, and leaves, have been investigated in STZ-induced diabetic rats as well. Red onion scales extract could improve the levels of fasting blood glucose and advanced glycation end products, enhance serum insulin level, and ameliorate diabetic nephropathy ( 84 ). The blood glucose and malondialdehyde (MDA) levels were declined in alloxan-induced diabetic rats fed with wheat bread supplemented with onion powder or onion peel extract ( 87 ). Onion seed extract showed a protective activity against the adverse side effects of diabetes in rats ( 77 ). The leaf extract of onion was found to ameliorate diabetes-induced neuropathic pain ( 106 ).

Onion exhibits antidiabetic potential in humans. In a randomized placebo-controlled clinical trial, daily ingestion of fresh yellow onion in breast cancer patients receiving doxorubicin-based chemotherapy was found to ameliorate the hyperglycemia and insulin resistance ( 96 ).

Overall, onion can fight against diabetes by reducing oxidative stress, moderating hyperglycemia, improving insulin resistance, and ameliorating various histopathological changes.

Anticancer Activity

Allium vegetables receive extensive concerns because of their beneficial effects against numerous diseases, especially in treating cancer and alleviating the side effects of current anticancer therapies, which are associated with their bioactive compounds, such as sulfur compounds, flavonoids, and saponins ( 161 , 162 ). The consumption of Allium vegetables was found to be negatively associated with the risk of diverse cancers, including breast cancer ( 163 ), gastric cancer ( 164 ), colorectal cancer ( 165 ), and upper aerodigestive tract cancers ( 166 ).

Many studies have been carried out to evaluate the anticancer activities of the common onion ( 92 , 163 , 167 – 169 ), other onion varieties, such as Allium cepa L. var. proliferurn Regel and Allium cepa L. Aggregatum group ( 90 , 170 , 171 ), and other Allium species, such as garlic ( Allium sativum L.) ( 163 , 172 ), leek ( Allium ampeloprasum L.) ( 26 ), chive ( Allium schoenoprasum L.), Welsh onion ( Allium fistulosum L.) ( 173 ), Chinese onion ( Allium chinense ) ( 174 , 175 ), and wild edible onions ( Allium flavum and Allium carinatum ) ( 176 ). By in silico approach, it has been found that onion-derived quercetin and diosgenin may take a role in the prevention and treatment of cancer by targeting on axon guidance receptor, neuropilin-1 ( 167 ). Onion extract or its major bioactive compounds showed potent anticancer activities, including cytotoxic, antiproliferative, anti-migratory, and apoptosis-inducing activities, in different cancer cells, such as human cervical carcinoma cell line (HeLa), myeloma cancer cell line (P3U1), pancreatic cancer cell line (AsPC-1), larynx cancer cell line (HEP2), colon cancer cell lines (SW620 and HCT116), adenocarcinoma cell line (Caco-2), glioblastoma cell line (A1235), liver cancer cell line (HepG2), and breast cancer cell lines (MDA-MB-231 and MCF-7) (26, 128, 130–133, 139–141]. 8-C-(E-phenylethenyl)quercetin, a novel compound from onion/beef soup, could cause G(2) phase arrest and inhibit the proliferation of colon cancer cells, and induced autophagic cell death, but not apoptotic cell death, by activating extracellular signal-regulated kinase (ERK) ( 168 ). Onion A, a sulfur compound from onion, exhibited antitumor effects by inhibiting the activation of suppressing signal transducer and activator of transcription-3 (STAT3) in myeloid lineage cells, and impaired the development of subcutaneous tumor and lung metastasis in tumor-bearing mice ( 95 ). Spiraeoside, isolated from red onion skin, exhibited promising anti-cancer effect against HeLa cell, could promote apoptosis by activating the expression of caspase-3 and caspase-9 ( 94 ). Recently, it was found that the anticancer activities of onion extract were enhanced by encapsulating on nano chitosan in multiple cancer cell lines ( 94 ). Besides, a wild edible onion showed a synergistic anticancer effect with doxorubicin against human hepatoma (HepG2) and lung carcinoma (A549) cells, and could protect from doxorubicin-induced cytotoxicity in human normal fibroblasts (MRC-5) and in vivo zebrafish models ( 176 ). Moreover, the intake of fresh onion was reported to reduce fasting blood glucose and improve insulin sensitivity in doxorubicin-treated breast cancer patients ( 96 ). Therefore, onion is an excellent anticancer vegetable, but its anticancer effect should be further verified in more clinical trials.

Cardiovascular Protection

Studies have revealed that onion can effectively improve lipid profile and inhibit platelet aggregation, attenuating the incidence of cardiovascular diseases. The methanol extract, quercetin, and quercetin glucosides from onion were found to inhibit collagen-induced platelet aggregation by using rat platelet-rich plasma ( 97 ).

Many studies have focused on the hypocholesterolemic effect of onion and its bioactive compounds in rodents fed with high-cholesterol or high-fat diets. Onion could effectively decrease the levels of total cholesterol, triglyceride, and low-density lipoprotein cholesterol in hyperlipidemic animals ( 98 , 101 , 177 ). Li et al. ( 101 ) reported that polyphenol-rich onion extract ameliorated hyperlipidemia with upregulation of low-density lipoprotein receptor (LDLR) and downregulation of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase (HMGCR) in the liver of Sprague-Dawley rats. Kang et al. ( 98 ) found that quercetin-rich onion peel extract resulted in a higher level of fecal cholesterol, and lower values of atherogenic index and cardiac risk factor in high-cholesterol diet-fed mice, with upregulation of LDLR and cholesterol 7-α-monooxygenase (CYP7A1), indicating the cholesterol-lowering effect of onion via fecal excretion. The fecal bile acid content was reported to be modified by the dietary addition of onion in high-cholesterol diet-fed rats ( 178 ). Dietary onion significantly increased the activity of antioxidant enzymes and improved the anti-inflammatory response and cardiovascular risk biomarkers in rats fed with a high-cholesterol diet ( 10 ). Besides, the high-cholesterol diet-induced shifts in the lipid mediators, such as oxylipin and sphingolipid profiles, were also found to be modified by the dietary supplementation of onion in hypercholesterolemic Wistar rats ( 100 ). The antihyperlipidemic potentials of fermented onion and onion volatile oils were investigated as well, and both of them had certain positive effects on hyperlipidemia animals ( 73 , 179 ). Moreover, the serum triglycerides levels were found to be reduced by consumption of steamed onion in overweight subjects ( 75 ). The intake of red wine extract of onion effectively reduced the total cholesterol and low-density lipoprotein cholesterol in healthy hypercholesterolemic subjects, while ameliorated the inflammatory responses and antioxidant defenses as well ( 102 ).

In addition, dietary fenugreek seeds and onion were reported to protect hyperglycemia-induced cardiac damage by inhibiting the activation of angiotensin-converting enzyme and angiotensin type 1 receptor in the heart of STZ-induced diabetic rats ( 80 ). Hypertension is known to be a key risk factor for cardiovascular disorders, however, the intake of quercetin from onion skin appeared to have no beneficial effects on blood pressure and endothelial function in subjects with hypertension ( 103 , 104 ). More animal studies and clinical trials are needed for better understanding the cardiovascular protective effects and related mechanisms of onions and their bioactive compounds.

Neuroprotection

Several studies have revealed that onion possesses anti-neuroinflammatory activity ( 6 , 156 ), ameliorates neuropathic pain ( 106 ), and exerts neuroprotective effects against Parkinson's disease ( 11 ), memory impairment ( 105 ), cerebral injury ( 108 ), and retinal damage ( 107 ).

The anti-neuroinflammatory activity of onion and its bioactive compounds was investigated by using the LPS-stimulated BV2 microglia culture model ( 6 , 156 ). Onion treatment prevented the LPS-induced increases of NO, TNF-α, IL-6, and IL-1β. The ameliorative effect of onion leave extract on neuropathic pain in rats was demonstrated by using two models, chronic constriction injury model and STZ-induced diabetic model ( 106 ). Onion leave extract significantly improved the behavioral and oxidative stress parameters as well as the sciatic nerve histopathological changes in both models. Onion ethanolic extract was reported to reduce malondialdehyde levels, ameliorate cognitive dysfunction, and prevent neuronal injury in 6-hydroxydopamine-induced rat model of Parkinson's disease ( 11 ). The neuroprotective effect of onion on learning and memory abilities was assessed in STZ-induced diabetic rats, and it was found that red onion ethanolic extract treatment could improve the learning and memory impairments in diabetic rats with reduced escape latency and traveled distance in Morris water maze test and increased step-through latency in passive avoidance test ( 105 ). The neuroprotective effect of onion on cerebral injury was evaluated in a cerebral ischemia/reperfusion mouse model, which was established by bilateral common carotid artery occlusion followed by reperfusion ( 108 ). It was revealed that the outer scale extract of onion could improve the memory and sensorimotor functions in cerebral injury mice by reducing cerebral infarct size and oxidative stress. The ischemia/reperfusion-induced retinal injury by pterygopalatine artery ligation in mice was used to investigate the neuroprotective effect of onion on neuronal damage, and it was found that onion water extract may protect from the retinal damage by regulating the expression of neurotrophic factors, such as B-cell lymphoma 2 (BCl-2), glial cell-derived neurotrophic factor (GDNF), glial fibrillary acidic protein (GFAP), and brain-specific homeobox/POU domain protein 3B (Brn3b) ( 107 ). Dietary fenugreek seeds and onion showed a protective effect on diabetic-cataract in STZ-induced diabetic rats ( 82 ).

Hepatorenal Protection

The intake of functional natural products or constituents has been considered as a complementary way for the management of liver and kidney diseases. Onion is rich in multiple bioactive compounds with hepatorenal protective activities.

The phenolic-rich extract of red onion peels protected against carbon tetrachloride-induced oxidative stress in the liver and kidney tissues of rats ( 12 ). Dietary onion ameliorated antioxidant defense in hypercholesterolemic rats with increased activities of SOD, CAT, and GPx in the liver ( 10 ). The doxorubicin-mediated hepatotoxicity, parenchymal necrosis, and biliary duct proliferation, were alleviated by pre-treating with onion extract in rats and this hepatoprotective effect was attributed to the antioxidant capabilities of onion extract, which reduced the levels of glutathione and malondialdehyde, while enhanced the levels of SOD and GPx in the liver ( 109 ). Diabetic nephropathy, including renal architecture and functional abnormalities as well as podocyte damages, was attenuated by dietary fenugreek seeds and onion in rats by inhibiting the renin-angiotensin system and glucose transporters ( 86 ). The STZ-induced diabetic nephropathy in rats was also ameliorated by treating with red onion scales extract, and it was found to be associated with its metabolite fingerprint ( 84 ). Besides, several metabolites and related metabolic pathways in the liver were reported to be modulated by the onion supplementation in hypercholesterolemic Wistar rats ( 178 ). The liver weight, lipid profile, and lipid mediators were found to be ameliorated by onion in hypercholesterolemic animals ( 98 , 100 ). Dietary intake of onion was revealed to lower hepatic steatosis, inflammation, and hepatic TNF-α expression in high-fat, high-sugar diet-fed rats ( 110 ). Moreover, the levels of alanine aminotransferase (ALT), a liver function marker, were significantly lower in healthy subjects with a daily intake of quercetin-rich onion, indicating that onion may be beneficial for improving liver function in humans ( 74 ).

Respiratory System Protection

Onion has been recommended for the treatment of respiratory disorders, such as coughs, asthma, and bronchitis. Several studies have demonstrated that onion could relax tracheal smooth muscle ( 111 ), ameliorate allergic asthma ( 13 ), reduce lung inflammation ( 68 ), and attenuate lung damage ( 112 ).

Onion exhibited relatively potent relaxant effects on potassium chloride or methacholine-contracted tracheal smooth muscle in a dose-dependent manner, and the calcium channel blockade and/or β2-adrenergic stimulatory were involved in these effects ( 111 ). The onion bulb extract was reported to inhibit house dust mite-induced increase in airway cellular influx and goblet cell hyper/metaplasia, reduce ex vivo eosinophil chemotaxis, and ameliorate peribronchial and perivascular inflammation ( 13 ). The preventive and anti-inflammatory activities of onion on tracheal responsiveness and lung inflammation was demonstrated in asthmatic rats, and it was found that drinking water with onion extracts significantly reduced tracheal responsiveness and lung inflammatory cells, including monocytes, neutrophils, and eosinophils ( 68 ). Besides, the levels of antioxidant enzymes, SOD and CAT, were increased in bronchoalveolar lavage fluids of the ovalbumin-sensitized rats treated with onion extract, while the levels of oxidant markers, such as malondialdehyde, nitrogen dioxide (NO 2 ), and nitrate (NO 3− ), were reduced ( 53 ). Reduction of lung malondialdehyde and elevation of lung SOD, CAT, and glutathione were also found in nicotine-induced lung damage rats treated with onion extract, which might be the main mechanism for the protective effect on lung damage ( 112 ). Moreover, the onion-derived bioactive compound, onionin A, was reported to inhibit lung metastasis in tumor-bearing mice ( 95 ).

Since the end of 2019, a new virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has triggered the worldwide pandemic of coronavirus disease 2019 (COVID-19). Up to January 2021, data from the web-based COVID-19 dashboard has shown that more than 100 million people were infected with more than two million deaths ( 180 ). The infection of SARS-CoV-2 may result in severe pneumonia, and the common symptoms of COVID-19 include fever, cough, nasal congestion, sore throat, and breathing difficulties ( 181 ). Studies have demonstrated that onion and its bioactive compounds could attenuate lung inflammation and protect against diverse respiratory disorders. Therefore, it may be possible that onion and its bioactive compounds have the potential to fight against SARS-CoV-2 and can be consumed in our diets for the prevention of COVID-19, which still needs further investigation.

Digestive System Protection

Onion has been shown to have a protective effect on the digestive system, such as mitigate gastric ulcer ( 113 , 182 ), modulate gut microbiota ( 114 – 116 , 183 ), and ameliorate colitis ( 14 , 69 , 116 ).

It has been reported that raw onion could inhibit histamine-induced gastric acid secretion and mitigate ethanol-stimulated gastric ulcer in rats, whereas boiled onion showed reduced potency ( 182 ). Alqasoumi ( 113 ) demonstrated that pre-treatment with onion could ameliorate gastric mucosal injury and ulcer index elicited by multiple factors, such as pylorus ligation, hypothermic restrainment, indomethacin, and necrotizing agents. Dietary supplementation of onion powders could modulate gut microbiota with an increased number of lactic acid bacteria in common carp juveniles ( 183 ). Onion could also be added into poultry feed as a natural growth promoter, which exhibited a positive effect on gut microbiota and intestinal histomorphology ( 55 , 114 ). Onion-derived bioactive compounds, such as quercetin and quercetin monoglycosides, were found to enhance the enzymatic activity of gut microbiota in rats ( 115 ). Quercetin monoglycosides were reported to modulate the diversity of gut microbiota in colitis mice induced by dextran sodium sulfate ( 116 ). Moreover, the severity of colitis in mice was revealed to be reduced by administering with onion bulb extract, no matter it was given before, after, or at the same time of the colitis induction ( 14 , 69 ). Besides, Allium species, including onion, showed protective effects against upper aerodigestive tract and gastrointestinal cancers ( 164 – 166 , 168 ).

Reproductive System Protection

Infertility has been considered a public health problem. Studies have shown that onion exhibited protective effects against adverse effects of chemical toxicity ( 119 – 122 ) and bacterial infection ( 118 ) on reproductive system, and could improve fertility and the quality of sperm and egg ( 15 , 126 ).

Testosterone, a steroid hormone, plays a key role in the development of male sexual characteristics, and its reduction may cause infertility ( 184 ). It has been reported that onion extract-contained cysteine sulfoxides could stimulate the production of the testosterone precursor, progesterone, by activating the protein kinase A signaling pathway in a testis-derived cell line (I-10) ( 117 ). Bacterial infection is one of the main factors that cause infertility in men. The adverse effects of Escherichia coli infection were reduced in male rats receiving onion juice, while the total antioxidant capacity and testosterone level was increased ( 118 ). Besides, onion could restore the permethrin-induced reductions in hormonal levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) as well as the expression of some key genes, such as luteinizing hormone/choriogonadotropin receptor (LHCGR) and steroidogenic factor 1 (SF1) ( 121 ). Onion also showed protective effects on testicle parameters and spermatogenesis in rats against the destructive effects of some insecticides or herbicides, such as permethrin, pyrethroid and paraquat ( 119 , 120 , 122 ). Onion seed extract was reported to have a protective activity against the negative effects of diabetes on the reproductive system in STZ-induced diabetic rats ( 77 ). Furthermore, the sperm quality and fertility were found to be improved in onion juice-treated adult male Wistar rats after the testicular torsion/detorsion ( 15 ). Recent study showed that onion juice could restore the erectile dysfunction induced by dutasteride in rats ( 125 ). Onion extract could prevent testicular damage induced by dexamethasone in rats ( 123 ) and the reproductive dysfunction in female rat offspring induced by maternal dexamethasone during lactation also found to be ameliorated by onion juice treatment ( 124 ). Dietary supplementation of onion extract was revealed to improve the egg quality and productive performance in laying hens ( 126 ). Moreover, onionin A showed an inhibitory effect on the progression of ovarian cancer by inhibiting tumor cell proliferation ( 9 ). In addition, results from clinical trials indicated that red onion intervention has certain beneficial effects in female subjects with polycystic ovarian syndrome ( 88 , 185 ).

Immune Modulation

Onion is thought to be beneficial for the immune system. Onion bulb extract showed an in vitro ability to induce the proliferation of human immune cells, particularly the CD 16+ natural killer cells ( 127 ). Another study demonstrated that onion-derived onionin A could improve the activity of lymphocyte and prevent the immunosuppressive activities of macrophages and myeloid-derived suppressor cell in the tumor microenvironment ( 95 ). An in vivo study showed that onion extract had a protective effect against dexamethasone-induced immunosuppressive effects in Wistar rats, such as ameliorating white blood cell counts, enhancing antioxidant activities, and increasing the levels of cytokines (TNF and IL-6) and immunoglobulins (IgG and IgM) ( 16 ). The immunomodulatory property of onion was demonstrated in ovalbumin-sensitized rats, and lower levels of IL-4 and IgE were found in sensitized rats treated with onion extract ( 53 ). Moreover, onion could be used as a natural immunostimulant added to animal feed to improve the growth performance and reduce the occurrence of diseases ( 55 , 183 , 186 ).

Other Health Functions of Onion

Browning of agro-products can lead to the deterioration of product quality and nutritional value, resulting in a decrease in consumer acceptance. Onion has been demonstrated to possess an inhibitory activity against the enzymatic browning reaction in fresh foods, such as fruit juice, mushrooms, and potato slices ( 187 – 190 ). In addition, intake of onion juice was reported to exhibit a beneficial effect on bone loss and bone mineral density by improving antioxidant capacity ( 57 ). Moreover, it has been revealed that fermented onion possessed an anti-photoaging effect against UVB-irradiation, probably by downregulating the expression of tyrosinase in B16F10 melanoma cells and collagenase-1 in UVB-induced HaCaT keratinocyte cells ( 191 ).

Potential Safety Concerns of Onion

Onion has been consumed as a vegetable and applied as an herbal medicine for a long history. Normally, onion and its bioactive compounds are quite safe for humans. However, several potential safety risks have raised concerns, for example, the residue of pesticides ( 17 ), bioaccumulation of heavy metals ( 18 , 19 ), and contamination of pathogenic microorganisms ( 20 , 21 ), which are discussed below.

Pesticide Residue

Pesticides with low toxicity and rapid degradation can be recommended for use in crops. However, the improper use of some pesticides in the onion crop may still cause health risks from onion consumption. Several studies have been carried out to investigate the degradation behavior, residue distribution, and dietary risk of different pesticides, including insecticides ( 17 , 192 ), fungicides ( 193 – 195 ), and herbicides ( 196 ), which were used for pest and disease protection and weed control in onion planting. Overall, the dietary risk of these pesticides through onion could be negligible with the reasonable usage does of pesticides and enough preharvest interval ( Table 2 ).

The residue decline and recommend preharvest interval of commonly used pesticides in onion.

a.i./ha, active ingredient per hectare; ×, recommended dosage .

Heavy Metal Enrichment

The enrichment of heavy metals, such as cadmium (Cd), lead (Pb), chromium (Cr), and nickel (Ni), in the farmland growing onion may induce the accumulation of heavy metals in onion and induce food safety issue. Bystricka et al. ( 197 ) reported that the content of Cd, Cr, and Pb exceeded the reference limits in the dry matter of onions from contaminated soil in the Slovak Republic, and different heavy metal enrichment capacities were found among the onion varieties. Cd and Pb contents in some Malaysian onions were reported beyond the permissible levels, and the planting site had a greater impact than onion varieties on heavy metal enrichment ( 19 ). Gashi et al. ( 198 ) demonstrated that the activity of delta-aminolevulinic acid dehydratase could be used as a sensitive biomarker for the risk assessment of bioaccumulation of heavy metals in onion. Yao et al. ( 199 ) developed a novel in situ imaging strategy for the fast evaluation of heavy metal enrichment in onion. Besides, Cd uptake in onion and other crops was revealed to be affected by environmental and edaphic factors ( 200 ). Indeed, the Cd accumulation in onion was reported to be mitigated by increasing the soil pH ( 18 ) or the application of silicon fertilizer to the soil ( 201 ).

Microbial Contamination

The use of sanitizer, sodium hypochlorite, combined with elevated CO 2 /reduced O 2 in package atmosphere was found beneficial for the safety and quality of fresh-cut onion, which showed effective inhibitory effects on the growth of Salmonella typhimurium , mesophilic aerobic bacteria, yeasts, and molds during storage ( 202 ). Moreover, the pathogenic microorganisms, including Listeria monocytogenes ( 21 ), Escherichia coli ( 203 , 204 ), Salmonella spp. ( 205 ), and mold ( 20 ) in onion infected by contaminated irrigation water or transferred from contaminated workplace are also considered as potential health risks. The microwave-integrated cold plasma treatment was reported to be a potential technology for non-thermal decontamination of onion powder ( 206 ). In addition, improving monitoring of the quality of irrigation water as well as the regular decontamination of the workplace may be the effective ways to reduce the risk of pathogen exposure in onion.

Conclusions

Onion is a widely cultivated and consumed vegetable, and contains various bioactive components. The sulfur-containing compounds, such as onionin A and cysteine sulfoxide, as well as the phenolic compounds, such as quercetin and quercetin glucosides, are the main bioactive constituents in onion and contribute to its multiple health functions, including antioxidant, antimicrobial, anti-inflammatory, and immunomodulatory properties. Moreover, onion can be a promising natural resource to develop functional foods or nutraceuticals for the prevention and management of certain diseases, such as obesity, diabetes, cancers, cardiovascular diseases, neurodegenerative diseases, nephropathy, respiratory disorders, colitis, and infertility.

At present, both in vitro and in vivo evidence suggests that onion powder, juice, and extracts exhibit multiple health functions. Although several bioactive compounds have been found to contribute to these functions, more bioactive compounds from onion or its by-products should be identified, and their health functions, the relevant molecular mechanisms, and whether they have synergistic effects need to be illuminated in the future. Currently, most studies focused on the health functions of the raw onion, it is necessary to investigate whether the cooking processing can impact its health benefits. Moreover, more well-designed clinical trials are still required to verify the health benefits of onion and onion-derived bioactive compounds in humans. Last but not the least, safety issues of onion should always be aware of, not only the contaminations mentioned in this review, but also other potential risks, such as the overdose of bioactive compounds.

Author Contributions

X-XZ, F-JL, and HL drafted the manuscript. H-BL, D-TW, FG, WM, YW, B-HM, and R-YG critically revised the manuscript. R-YG and B-HM conceived the idea and scientific guidance through the process. All authors have read and agreed to the published version of the manuscript.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding. This research was funded by the Central Public-interest Scientific Institution Basal Research Fund of China (No. Y184XK05) and the Local Financial Funds of National Agricultural Science and Technology Center, Chengdu, China (No. NASC2021KR01).

Onions--a global benefit to health

Affiliation.

• 1 Department of Plant Genetics and Biotechnology, Horticulture Research International, Wellesbourne CV35 9EF, UK. [email protected]
• PMID: 12410539
• DOI: 10.1002/ptr.1222

Onion (Allium cepa L.) is botanically included in the Liliaceae and species are found across a wide range of latitudes and altitudes in Europe, Asia, N. America and Africa. World onion production has increased by at least 25% over the past 10 years with current production being around 44 million tonnes making it the second most important horticultural crop after tomatoes. Because of their storage characteristics and durability for shipping, onions have always been traded more widely than most vegetables. Onions are versatile and are often used as an ingredient in many dishes and are accepted by almost all traditions and cultures. Onion consumption is increasing significantly, particularly in the USA and this is partly because of heavy promotion that links flavour and health. Onions are rich in two chemical groups that have perceived benefits to human health. These are the flavonoids and the alk(en)yl cysteine sulphoxides (ACSOs). Two flavonoid subgroups are found in onion, the anthocyanins, which impart a red/purple colour to some varieties and flavanols such as quercetin and its derivatives responsible for the yellow and brown skins of many other varieties. The ACSOs are the flavour precursors, which, when cleaved by the enzyme alliinase, generate the characteristic odour and taste of onion. The downstream products are a complex mixture of compounds which include thiosulphinates, thiosulphonates, mono-, di- and tri-sulphides. Compounds from onion have been reported to have a range of health benefits which include anticarcinogenic properties, antiplatelet activity, antithrombotic activity, antiasthmatic and antibiotic effects. Here we review the agronomy of the onion crop, the biochemistry of the health compounds and report on recent clinical data obtained using extracts from this species. Where appropriate we have compared the data with that obtained from garlic (Allium sativum L.) for which more information is widely available.

Copyright 2002 John Wiley & Sons, Ltd.

Publication types

• Research Support, Non-U.S. Gov't
• Flavonoids / chemistry
• Flavonoids / therapeutic use
• Global Health
• Onions* / chemistry
• Onions* / growth & development
• Phytotherapy*
• Plant Extracts / chemistry
• Plant Extracts / therapeutic use
• Quercetin / chemistry
• Quercetin / therapeutic use
• Sulfoxides / chemistry
• Sulfoxides / therapeutic use
• Plant Extracts

Blog 132-Research Onion: A Systematic Approach to Designing Research Methodology

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Developing a good research design is important while undertaking quality social science research, and in this blog Dr Mahesh BT illustrates the different stages in designing a research methodology using the Research Onion framework.

When I joined for my PhD, as many of you, I too was curious about research. Along with the curiosity came seriousness, but only after one of my mentors said: “Your thesis is your brainchild and indeed a reflection of you”. I am here now to share a few of the specifics that I learnt during my PhD journey. I will be discussing how to design and present a robust research methodology. Why do I find this concept very crucial? It is because these answers to research questions are valid and reliable – if they are answered through a systematic method(s). Often we find dissertations with a poorly explained research methodology chapter, which is required to be crystal clear in every step, so I was in search of something that can explain things clearly. During my desk research, I came across various ways and means to design research methodology; one of the most crucial revelations for me was a research vegetable called ‘Research onion’. Let us first see what this research onion is all about.

WHAT IS ‘RESEARCH ONION’?

Saunders et al. (2012) proposed the research onion framework (Figure 1), which explains pictorially the various aspects of the research to be examined and planned in order to come up with a sound research design. In other words, the research onion guides the researcher through all the steps that need to be taken when developing a research methodology.

Saunders et al. (2019), divided the research onion into three levels of decisions: 1. First two outer rings, i.e., Research philosophy and Research approach; 2. Research design which constitutes (a) methodological choices, (b) research strategy and (c) time horizon; and (3) tactics, i.e., the inner core of the research onion, which includes data collection and analysis aspects.

Before we strip the research onion let us do an activity. Take an onion and try to peel it from the inside without using a knife. You tried but could not peel it, the systematic way is to peel it from the outside to inside, and this is what we have to do with the research onion as well.

To develop a sound research methodology scholarly research starts with the research question(s), the objectives followed by the series of decisions on choice of research philosophy, approach to research, then the research design, i.e., methodological choices, research strategy, the time horizon, and the last inner core – data collection and data analysis. All the layers of research onion are interrelated and interdependent. In other words, the choice of philosophy influences the approach, which in turn influences the selection of methodological choice, strategy, time horizon, data collection and analysis.

PEELING OUT THE RESEARCH ONION 

1.RESEARCH PHILOSOPHY Knowingly or unknowingly a researcher will be making numerous assumptions while embarking on research (Burrell and Morgan 2016).

These assumptions are of three types:

• Ontological assumptions –  Assumptions regarding the reality faced in the research or what makes something a reality, and how a researcher can understand existence.
• Epistemological assumptions – Assumptions associated with human knowledge or what forms valid knowledge, whether it can be known, and how a researcher can get it and transfer it.
• Axiological assumptions  -These are assumptions about the level of influence of the researcher’s values on the research process or what is essential and valuable in the research.

Further, these assumptions help a researcher to design the research questions, choose appropriate methods, and influence the interpretation of findings (Crotty 1998). These assumptions altogether form the research philosophy of the study. According to Saunders et al. (2012), the term research philosophy refers to ‘a system of beliefs and assumptions about the development of knowledge’.

The  ontological assumption  is the assumption made by a researcher regarding the nature of reality. Here reality means the study area or a subject domain, such as agricultural extension. The extension fraternity has various assumptions regarding the subject of extension, we assume it to be a study of human (farmers) behaviour, and others say it is the transfer of technology, and so on and so forth. These ontological assumptions may also be with regard to a specific research area in the subject domain. For instance, we study farmers’ adoption of agro-technology, in most adoption studies the researchers presumed that a lower level of adoption (a reality) of technology is the reason for lower crop production. Therefore, the focus was on studying the level of adoption by farmers and how to increase it. On the other hand, some researchers assume technology adoption as a mental process and see that there is low level of adoption everywhere, and so they try to understand why there is a low level of adoption and what are the factors determining the adoption. From this, it is clear that your assumption about the nature of reality (ontology) decides how you view the subject domain (Agricultural Extension) or the research area, which in turn influences what you want to research (what research questions to ask or what research objectives to study).

The  epistemological assumption  is an assumption made by a researcher regarding knowledge. What forms valid and reliable knowledge? How do we acquire and communicate it? We know that the subject matter of agricultural extension is derived from different disciplines. Therefore, the nature of knowledge will be diverse; it may constitute numerical data (e.g., number of women FPOs) to textual data (results of in-depth interview or focused group discussion), or even visual data (social map, resource map, sociogram). In extension research, facts, opinions, narratives and stories constitute valid knowledge, provided it follows a systematic process of enquiry. You will come across various research studies in extension where the researcher has used different epistemology in their research, research purely based on case studies, and some dealing only with factual stuff.

The  axiological assumption  is an assumption made by a researcher regarding the influence of values and beliefs on the research. The researcher tries to be free from values and beliefs intruding into the research or positively considers and acknowledges values and beliefs influencing the research process and the conclusions. Sometimes we need to decide on whether the values and beliefs of the research respondents should be considered or not. Researchers argue, as reported by Saunders  et al.  (2019), that it is very tough to keep ourselves free from the influence of values and beliefs. For instance, as a researcher you might have come across your advisor saying “parametric test is stronger than non-parametric”, “qualitative data gives in-depth understanding about a phenomenon than quantitative data”. What are these assumptions? They are the aspects of research your advisor values more.

At this juncture, you might have questioned yourself – why should I be making assumptions and know the different research philosophies when I can directly collect data, analyse and report the results? There are several aspects for which these assumptions are essential they are listed below.

• Assumptions are your research tour guide; they tell you how to conduct the research, what should be your role – whether you should maintain objectivity or can subjectivity be expressed. They tell you what methods you can follow.
• The researcher has to defend his/her work at various levels. As a student researcher, we get suggestions from the advisory committee or institutional review board to strictly go for quantitative methods with probability sampling, and try to avoid qualitative methods. This is due to the difference in the assumptions or more specifically, the research philosophy they follow. The most challenging is to convince the journal reviewers and editors, there are chances of your paper getting rejected because your philosophy is different from what they follow. Therefore, to show that your overall approach to research is justifiable, you should state your assumptions (research philosophy) very clearly.
• Another issue we come across is sweeping apologies in our dissertation, for instance, a researcher apologises for not interviewing a large number of respondents in qualitative research; and the other one is failing to get an in-depth understanding due to the quantitative nature of research. No! You need not apologise, all that you need to do is follow the standard methods and procedure that suits your research philosophy. Therefore it is very important to understand the various research philosophies.

According to Saunders  et al.  (2019), there are five research philosophies: (1) positivism; (2) critical realism; (3) interpretivism; (4) postmodernism; and (5) pragmatism. The detailed explanation of these five research philosophies is presented in Tables 1 to 5.

2. THE RESEARCH APPROACH OR APPROACH TO THEORY DEVELOPMENT

The second ring in the research onion contains the research approach. If we critically think on what a researcher does in research, we can classify them into three aspects – theory testing, theory building, and theory modification. The point I am trying to make here is that the research we undertake involves the use of theory which we may or may not name in our research design. You will find the essence of theory in the conclusions of research findings. The selection of a particular philosophy that was discussed in the first section will determine the approach you choose for the development of the theory or for the reasoning behind your findings. Further, the approach you select will influence the choice of research design and methods (Babbie 2010).

Source: Developed from Saunders et al. (2019) Note: Application of positivist philosophy in social science research is a matter of scholarly debate. However, a researcher can apply some of the assumptions and methods with caution and rationality.  Suggested reading: Thomas Houghton, Does positivism really ‘work’ in the social sciences? Link: https://www.e-ir.info/2011/09/26/does-positivism-really-%E2%80%98work%E2%80%99-in-the-social-sciences/ 

Source: Developed from Saunders et al. (2019) Suggested reading : Fletcher Amber J. Applying critical realism in qualitative research: Methodology meets method.  Link:   https://www.tandfonline.com/doi/abs/10.1080/13645579.2016.1144401?journalCode=tsrm20 

Source: Developed from Saunders et al. (2019) Suggested reading : Chen Y Y, Shek D T L and Bu F F. 2011. Applications of interpretive and constructionist research methods in adolescent research: Philosophy, principles and examples. International Journal of Adolescent Medicine and Health 23(2).doi:10.1515/ijamh.2011.022 https://pubmed.ncbi.nlm.nih.gov/21870675/

Source: Developed from Saunders et al. (2019) Suggested reading : Rosenau P V. Postmodernism: Methodology. https://doi.org/10.1016/B0-08-043076-7/00692-6    Link : https://www.sciencedirect.com/science/article/pii/B0080430767006926

Source: Developed from Saunders et al. (2019) Suggested reading: Crist J D, Parsons M L, Warner-Robbins C, Mullins M V and Espinosa Y M. 2009. Pragmatic action research with 2 vulnerable populations. Family & Community Health 32(4):320–329. doi:10.1097/fch.0b013e3181b9

According to Saunders et al. (2012), there are three research approaches viz., induction, deduction, and abduction. A brief overview of the research approaches is presented in Table 6.

2.1 In this section I have graphically explained all the three research approaches using flowchart with hypothetical examples. 2.1.1 Inductive approach to research

Suggested reading: Ferguson  K M, Kim M A and McCoy S. 2011. Enhancing empowerment and leadership among homeless youth in agency and community settings: A grounded theory approach. Child and Adolescent Social Work Journal 28(1):122.  https://doi.org/10.1007/s10560-010-0217-6

2.1.2 Deductive approach to research

Suggested reading: Chia-Pin Yu, Shu Tian Cole and Chancellor Charles. 2018. Resident support for tourism development in rural midwestern (USA) communities: Perceived tourism impacts and community quality of life perspective. Sustainability, MDPI, Open Access Journal 10(3):1-17.

2.1.3 Abductive approach to research

You may find some surprising or incomplete observations or conclusions regarding any social aspect; you wanted to study it both empirically as well as know the subjective opinions of people for better understanding. In this situation, you follow the abduction approach in which your research will combine the elements of both the inductive and deductive approaches. To put it in simple words, in abduction ‘You build a theory and then go for its empirical testing’.

Suggested reading: Bristow A, Robinso S K and Ratle O. 2017. Being an early-career CMS academic in the context of insecurity and ‘Excellence’: The dialectics of resistance and compliance. Organization Studies 38(9):1185–1207.

Research design:  It is the overall plan of a research project which involves three distinct but interrelated aspects. They are: methodological choice, research strategy and time horizon. Let us understand them separately. Sanders et al. (2019) classified research designs into three types: (1) quantitative research design; (2) qualitative research design; and (3) mixed methods research design. I have attempted to develop a schematic explanation for qualitative and quantitative research design (Figures 4 and 5, respectively) for better understanding.

3. METHODOLOGICAL CHOICE

Methodological Choice involves   the selection and use of a quantitative, qualitative, or mixed methods research design. In the mono method, a single data collection technique is utilized, followed by corresponding qualitative or quantitative analysis procedures. In the multiple method design, more than one data collection techniques and analysis procedures are employed (Collis and Hussey 2013). Alternatively, a mixed-method approach utilizes both qualitative and quantitative data collection techniques and analysis procedures (Creswell 2013).

According to Saunders et al. (2019), mixed method research can be classified into three ways which are as follows:

• Concurrent mixed methods research: Here a researcher collects both qualitative and quantitative data and analyses them in a single phase study.
• Sequential mixed methods research : Here a researcher collects and analyses data in two phases, which can further be divided into two forms:
• sequential exploratory research design: where a researcher collects and analyses qualitative data in the first phase, followed by quantitative data collection and analysis in the second phase;
• sequential explanatory research design: Here a researcher collects and analyses quantitative data in the first phase followed by qualitative data collection and analysis in the second phase.
• Sequential multi-phase: In this a researcher collects and analyses data in more than two phases, in sequence. For example, qualitative followed by quantitative and then qualitative.

4. THE RESEARCH STRATEGY

The research strategy describes how the researcher aims to carry out the work (Saunders  et al . 2007). There are several research strategies, viz., Experimental design, Survey design, Archival research, Case study, Ethnography, Action research, Grounded theory and Narrative inquiry (Saunders  et al. 2012). Here we can include other research strategies appropriate to our study.

• Experimental design : Here, a researcher tries to study a cause-effect relationship between two or more variables. He/she decides to systematically manipulate the independent variable to study the corresponding changes in the dependent variable.
• Survey design:  Here, a researcher tries to seek answers for ‘what’, ‘who’, ‘where’, ‘how much’ and ‘how many’ types of research questions. Data is collected and analyzed from a sample of individuals.
• Case study: is an empirical inquiry of an individual social unit. Here the researcher tries to seek answers for ‘how’ and ‘why’ questions.
• Action research : A systematic inquiry to address real-life practical problems. Here a researcher tries to find practical solutions for problems through participation and collaboration with members of a social unit.
• Grounded theory:  This is a systematic inductive method for conducting qualitative research to develop a theory.
• Ethnography : is a research strategy adopted to explore cultures and societies. Here a researcher collects data through direct interaction and involvement so as to gain firsthand information from research subjects.
• Archival research: A systematic inquiry wherein primary sources held in archives are studied for evidence collection or deep understanding. Here a researcher does not use secondary sources relevant to the research topic.

5. TIME HORIZON

Research can be grouped into two types based on time, i.e., longitudinal or successive independent samples; and cross-sectional (Bryman and Bell 2015). The longitudinal study refers to the study of a phenomenon or a population over a period of time (Caruana et al. 2015). A cross-sectional study is a ‘snap-shot’ study, it means a phenomenon or a cross-section of the population is studied for one time (Setia 2016). Please read the suggested reading given below to understand one of the longest researches in the history of social science research.

Suggested reading: Hastorf A H 1997. Lewis Terman’s longitudinal study of the intellectually gifted: Early research, recent investigations and the future. Gifted and Talented International 12(1):3–7. doi:10.1080/15332276.1997.11672858

6. DATA COLLECTION AND ANALYSIS 

  The inner circle of research onion is made up of ‘tactics’ which refers to aspects   about the finer details of data collection and analysis. In this section, the following aspects are described.

A. Data collection tools and procedures : Data collection tools such as scale, questionnaire, mail survey, etc., and procedures such as scale construction, interviews, focused group discussion, etc. B. Study Area – A brief description about the study area and why you have selected this locale, supported by reliable data. C. Research population and sampling procedures : Describe the following aspects in this section:

a. Inclusion /exclusion criteria; b. Sample size; c. Sampling method; d. Sampling plan – Flow chart with a table indicating sample details; e. Sourcing samples : Here the researcher has to describe the source of the study samples; it has the following three aspects:

• Source population(N) : This is the group about which the researcher is going to draw inferences and to which the inclusion and exclusion criteria are applied (Example: women farmers of a district – say may be N=1000);
• Study population  (Np): The group which fits the inclusion and exclusion criteria (Example: women farmer growing sunflower, with landholding more than 2 ha and five years of experience, say maybe Np=500);
• Sample (n) : The group selected after following a suitable sampling method, and finally with whom you conduct your study (a representative sample of women sunflower growers sampled from the study population, say maybe n=120).

f.  Sample limitations

D. Study Phases:  describe in how many phases your study will be done (during planning-synopsis) / was done (while reporting in the thesis) if it was done in multiple phases. Explain the list of the tasks using a Gantt chart (Figure 6).

Variables and their measurement:  Describe how the concepts, constructs and the variables were identified; this aspect is linked with the theoretical orientation. Provide the operational definition; it means how the variable is measured, mention the level of measurement also. A schematic table would suffice (for example, see Table 7).

Table 7. List of variables their method of measurement and operational definition

F. Statistical analysis: Mention all the statistics tools applied and software(s) used to analyse the research data (in thesis).

G. Ethical considerations: All the ethical aspects considered in the study need to be clearly planned and mentioned. Mention about respondent consent, how sensitive information (in synopsis) was elicited, if any. Report the approval of Research ethics committees, if applicable.

The difference between a researcher and a non-researcher is, whatever a researcher does she/he does it systematically, justifies logically, subjects it to verification, is always open to criticism, ready for self-correction and explicitly expresses what was done, how it was done, why it was done and what was found. A researcher starts with a research problem, raises questions, and transforms it into workable objectives. To find answers to the research questions, we need a sound research methodology. Research onion is one such framework that helps in designing a robust research methodology; simply put, it will help you to make a series of decisions that allows systematic research. We began with three assumptions, viz., ontological, epistemological and axiological, which constitute our research philosophy. Once we decide on the specific philosophy, an appropriate research approach can be adopted based on the research question and philosophy. The deductive approach is adopted for theory testing, inductive approach for theory building, and abductive approach for theory modification.

Further, these two crucial decisions will guide the next important aspect that is research design, which is made up of three important decisions: 1. Methodological choice – whether to follow a qualitative method, quantitative method or a mixed method; 2. Research strategy; and 3. Time horizon – cross-sectional or longitudinal research. Furthermore, the last decision is about very minute intricacies of research that is data collection, analysis and ethical statement.

Authors’ observation

It is often observed in academic discussions that various aspects of research are presented and (or) perceived to be competitive (quantitative versus qualitative, parametric versus non-parametric, probability sampling versus non-probability sampling, small sample size versus large sample size, experimental design versus non-experimental, cross-sectional versus longitudinal, and so on) rather than complimentary. Every aspect of research has got its own importance and relevance. A research scholar values every logical approach to research, and it is possible only after looking at it through all dimensions via the lenses of different questions (why, what, when, where, who, what).

Acknowledgement

I wish to acknowledge and thank the AESA, CRISP, ICAR-CTCRI, MANAGE, NAARM collaborative National Workshop on ‘Advances in Social and Behavioural Science Research’ held from 12 to 17 November 2018 at ICAR-CTCRI, Kerala. This event was an eye opener for me which oriented me towards social science research methodology, and indirectly helped me in my PhD research.  

Babbie E. 2010. The practice of social research. 12th Edition. Belmont, USA: Wadsworth.

Bristow A, Robinson S K and Ratle O. 2017.Being an early career CMS academic in the context of insecurity and ‘Excellence’: The dialectics of resistance and compliance’. Organization Studies 38(9):1185–1207.

Bryman A and Bell E. 2015. Business research methods Oxford: Oxford University Press.

Burrell G and Morgan G. 2016. Sociological paradigms and organisational analysis. Abingdon: Routledge (originally published by Heinemann 1979).

Caruana E J, Marius Roman, Jules Hernández-Sánchez and Piergiorgio Soll. 2015. Longitudinal studies. Journal of Thoracic Disease 7(11):537–540. doi: 10.3978/j.issn.2072-1439.2015.10.63. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4669300/

Chen Y Y, Shek D T L and Bu F F. 2011. Applications of interpretive and constructionist research methods in adolescent research: Philosophy, principles and examples. International Journal of Adolescent Medicine and Health 23(2).  doi:10.1515/ijamh.2011.022  https://pubmed.ncbi.nlm.nih.gov/21870675/

Chia-Pin Yu, Shu Tian Cole and Charles Chancellor.2018. Resident support for tourism development in rural midwestern (USA) communities: Perceived tourism impacts and community quality of life perspective. Sustainability, MDPI, Open Access Journal 10(3):1-17.

Crist J D, Parsons M L, Warner-Robbins C, Mullins M V and Espinosa Y M. 2009. Pragmatic action research with 2 vulnerable populations. Family & Community Health 32(4):320–329. doi:10.1097/fch.0b013e3181b91f

Crotty M. 1998. The foundations of social research: Meaning and perspective in the research process. London: Sage.

Collis J and Hussey R. 2013. Business research: A practical guide for undergraduate and postgraduate students. Macmillan International Higher Education.

Creswell J W. 2013. Qualitative inquiry & research design; choosing among five approaches. Third edition. Thousand Oaks, CA: Sage.

Ferguson K M, Kim M A and  McCoy S. 2011. Enhancing empowerment and leadership among homeless youth in agency and community settings: A grounded theory approach. Child and Adolescent Social Work Journal 28(1):1-22.  https://doi.org/10.1007/s10560-010-0217-6

Hastorf A H. 1997. Lewis Terman’s longitudinal study of the intellectually gifted: Early research, recent investigations and the future. Gifted and Talented International 12(1):3–7. doi:10.1080/15332276.1997.11672858

Saunders M, Lewis P and Thornhill A. 2007. Research methods for business students. (6th ed.) London: Pearson.

Saunders M, Lewis P and Thornhill A. 2019. Research methods for business students. Eighth edition. London: Pearson.

Setia M S. 2016. Methodology series module 3: Cross-sectional studies. Indian Journal of Dermatology 61:261-4. Retrieved from  http://www.e-ijd.org/text.asp?2016/61/3/261/182410

Thomas Houghton. 2011.Does positivism really ‘work’ in the social sciences? Link: https://www.e-ir.info/2011/09/26/does-positivism-really %E2%80%98work%E2%80%99-in-the-social-sciences/

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Very interesting blog. Enjoyed reading it. I do have a small difference of with respect to one of the statements. Author says ‘you need not be apologetic in saying that sample was small or methods limit interpretation’. I am a firm believer of transparent communication and I feel that it is the role of a researcher to know the limits of the study and also communicate it to the readers, and there is nothing to be apologetic about it (Bsically I disagree with the term too). Infact I see many paper where they make very strong causal statements, when the methods are not really designed for it which I see as a more serious concern. This is my humble opinion, as academician I really enjoyed the blog. I appreciate the efforts of the author in elaborating on a very Important topic.

Thank you Aditya, thank you for your observations and. The very purpose of this blog was to make things systematic and clear. Yes the author strongly believe in reporting every aspect of the research including limitations provided they are indeed limiting the research design. Here the author is trying to state that when the research design demands or permits certain conditions those conditions should not be expressed as limitations, and it doesn’t imply any aspect should be hidden. I welcome your disagreements in the usage of words, we can disagree to agree. I strongly agree with you that even I enjoyed working on this blog. Thank you once again.

Well written.

Very comprehensively covering different paradigms in research methodology, with interesting analogy, Dr Mahesh could peel out research onion, explaining each layer starting from research philosophy to the data collection. Congratulations to Dr Mahesh. Further one important inner layer could be added to the onion, which would make it complete-the layer of research reporting/research communication. Unless we plan how we are going to communicate our research to the others, and communicate effectively through research paper, conference etc., research remains incomplete.

Very Good effort to write the blog to make research methodology easy to understand, Dear Mahesh , I enjoyed reading it

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Understanding the Research Onion

The research onion model.

The research onion model was presented by Saunders, Lewis and Thornhill in their book titled Research Methods for Business Students . This model aims to explain the different stages of writing a dissertation to help students create a better organised methodology. The below Research Onion model symbolically illustrates the ways in which different elements involved in the research could be examined to develop the final research design.

Layers of the Research Onion

The research onion consists of six main layers, which can be explained as:

It refers to the set of principles concerning the worldview or stance from which the research is conducted. It is usually studied in terms of ontology and epistemology. Here, ontology refers to the authenticity of the information and how one understands its existence, whereas epistemology refers to the valid information required for the research and how one can obtain it. Philosophical positions used in academic studies are often divided into positivism and interpretivism, where positivism assumes that knowledge is independent of the subject being studied, and interpretivism claims that individual observers have their own perception and understanding of reality. Hence positivist studies are often more scientific and result in testing phenomena, whereas interpretivist studies are often qualitative in nature.

Once the student has chosen the appropriate methodology, the research onion suggests that an appropriate research must be picked. The deductive approach starts with a specific hypothesis development based on the literature review that has been observed by the researcher, and gradually tries to test this hypothesis and check if it holds in particular contexts. In contrast, the inductive approach starts with observations that the researcher uses to create a new theory.

After this, the student is expected to devise the strategy of the study. The research onion suggests that strategies can include action research, experimental research, interviews, surveys, case study research or a systematic literature review. The strategy is chosen based on the data required for the research and the purpose of the study.

Choices of Methods

The research onion suggests mono-method, mixed method and multi-method as possible choices for conducting research. The mono-method comprises only one method for the study. The mixed method is based on the use of two or more methods of research and commonly refers to the use of qualitative and quantitative methodology. Finally, the multi-method uses a wider selection of methods.

Time Horizons

It refers to the time frame of the research. Generally, observations can be of two types based on time horizons, namely cross-sectional and longitudinal. The cross-sectional data is used when all observations are for a single point of time such as in most surveys. Longitudinal data, in contrast, implies the observations for a particular variable that are available for several years, quarters, months or days.

Data Collection and Analysis

This is the final layer of the research onion and consists of the techniques and procedures used. It is used to clearly explain the ways and purposes of the research conducted. At this stage, the student is expected to choose between the primary and secondary data and between qualitative and quantitative data collected from different sources. Data is considered the central piece in the research onion framework.

If you are struggling with choosing the right methods for your dissertation, feel free to use our methodology generator tool that uses elements of the research onion.

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Understanding the Research Onion (Saunders et al., 2015)

• January 18, 2024

• Published: Jan. 18, 2024

This article provides a comprehensive guide to understanding and writing a compelling and effective research methodology chapter of your thesis/dissertation, focusing specifically on the research onion framework by Saunders, Lewis, and Thornhill (2016) .

Table of Contents

Introduction.

Research is an incredibly important tool for understanding and navigating through the world around us. It is defined as a systematic and structured process of gathering data, analyzing information, and drawing conclusions in order to answer research questions or address a specific problem. Research plays a crucial role in shaping policies, decision-making, validating existing ideas, and gaining insights into how the world operates (Sujatha, 2016)

However, conducting research is not an easy task. It often involves a continuous process of inquiry and response, leading to a multitude of questions such as: where do I start from? What research questions should I formulate? What research design or philosophy is best for my study? How do I select the suitable method for data collection/analysis? 

Recent statistics show that academic research demands rigorous commitment and resilience. A study by Styger Vuuren and Heymans (2014) revealed that, in South African universities , the dropout rates for Master’s degrees ranged from 30% to 67% , while for doctoral degrees, the rates were between 50% and 68% . Similarly, Bekova and Dzhafarova (2019) reported that the dropout rate for certain Ph.D. programs in Spain ranges 70% to 90% , while in Australia , it was approximately 30% , and around 50% in the USA . Even the most developed European countries face 40% to 50% dropout rate of engineering students during their first year, and the rate can be as high as 80% for some engineering disciplines (Sultana et al., 2017; Kabashi et al., 2022).

The high dropout rates for postgraduate students can be attributed to a multitude of factors, including individual, institutional, and sociodemographic considerations.

Individual-related factors such as mental health, regret, anxiety, and age have been identified as potential contributors to dropout intentions among postgraduate students (Peng et al., 2022; Nadeem & Palaniappan, 2021). Additionally, the demanding nature of postgraduate studies, inadequate research preparation, and insufficient institutional and financial support have been highlighted as intrinsic (student-related) and extrinsic (institutional-related) factors influencing dropout rates (Cobbing et al., 2017). Furthermore, gender disparities and educational equality have been associated with higher dropout rates among postgraduate female students compared to their male counterparts (Alabi et al., 2019). Socioeconomic factors, such as the cost of education and economic background, have also been recognized as influential in student dropout from postgraduate studies (Nadeem, Palaniappan & Haider, 2021).

Furthermore, institutional factors, such as inexperienced and overburdened supervisors, inadequate research preparation, and insufficient institutional and financial support, have also been recognized as contributors to the high dropout rates for postgraduate students (Cobbing et al., 2017; Styger et al., 2014). Furthermore, the lack of adequate computer literacy, typing skills, and effective internet usage among postgraduate students has been identified as a challenge, particularly in the context of coursework and research (Havenga & Sengane, 2018).

The lack of proper guidance or academic counseling is yet another factor that has been identified as a significant obstacle contributing to the dropout rates of postgraduate students (Schmidt & Umans, 2014; Deri, 2022). Without proper career guidance or academic counseling, students may find themselves in courses that do not align with their interests or career aspirations, leading to dissatisfaction, prolonged or non-completed  studies (Schmidt & Umans, 2014) and, eventually, dropout. Additionally, the lack of experience and competencies in academic writing has been cited as a barrier to progression for PhD students (Litalien & Guay, 2015).

However, despite the complexity and challenges of conducting research, it is important to highlight that there are many resources and tools available to help researchers navigate the process and write a compelling and effective research methodology chapter. One such resource is the research onion framework (Saunders et al., 2016), which provides a comprehensive structure for conducting research and effectively organizing the methodology chapter. The framework provides a roadmap to guide a researcher from the initial stage of a project to the finished product.

In this comprehensive article, we will delve deeper into the research onion framework and explore in detail how it can be effectively used to write a compelling research methodology chapter for your dissertation/thesis. We will also discuss some common misconceptions about research methods and how understanding the onion can help researchers avoid these errors.

1. Defining the Research Onion

The research onion is a concept that describes the stages of planning and designing a research project. It is a metaphorical model used in research methodology to illustrate the various layers or stages involved in the research process. It is based on the idea of layering, with each layer representing a different stage of the research process.

As the word suggests, this process is similar to peeling an onion; as you go deeper into your research project, you will see more layers that need to be peeled off before reaching the core of your data analysis. Each layer of the onion represents a different step in the process of conducting research, and each step builds upon the previous one. The main idea behind the research onion is that researchers need to understand how their decisions at each stage can affect the quality and validity of their findings.

The concept was first developed by Saunders, Lewis, and Thornhill (2009) to visualize the research process and the various stages researchers must go through to achieve a successful outcome. 

The research onion consists of six layers: (1) the research philosophy, (2) the research approach, (3) the research strategy, (4) the research choice, (5) the time horizon, and (6) the data sources. Each layer of the onion has a unique purpose and is fundamental to the success of a research project. The overall research will likely suffer if any of these layers is neglected. Therefore, researchers need to understand the research onion concept and how the layers interact with each other. This understanding can give them the confidence to accurately plan, design, and execute their research projects and ensure that the results are valid and reliable. 

2. The Research Onion's Layers

The diagram below shows the structure of the onion and how each layer provides a different perspective on the research process:

2.1. Research Philosophies

The first layer of the research onion is the research philosophy. This is the outermost layer and represents the researcher’s underlying philosophical beliefs and assumptions. Research philosophy is about how you view the world. It includes your beliefs about the nature of the truth you are investigating: WHAT is important, and WHY is it important?

As such, the researcher should be able to answer the following questions: what personal values do you bring to the topic? How will they influence your choice of methodologies and procedures? What impact might they have on the validity of your results? Bajpai (2011) suggested the research philosophy helps you decide what types of data to collect, how to collect it, and how to analyze it.

Academic studies frequently adopt four distinct philosophical orientations in research: positivism, interpretivism, pragmatism, and realism (Saunders et al., 2007; Žukauskas, Vveinhardt, & Andriukaitienė, 2018).

1.1. Positivism

Positivism is based on the assumption that the world is objective and that scientific methods are the best way to understand it. The advocates of positivism support the idea of objectivism. In other words, reality can be known objectively through systematic observation and measurement. From this viewpoint, researchers are considered objective observers who examine phenomena that are independent of them (Rehman and Alharthi, 2016). They use symbols and words to describe things as they exist without any interference (Rehman & Alharthi, 2016).

The positivist approach is fundamentally rooted in scientific methods, diligently attempting to explain the underlying causes and effects of various phenomena. It is particularly well-suited for quantitative studies, where researchers employ techniques such as surveys, experiments, and simulations to rigorously gather and analyze data (Holden & Lynch, 2004).

1.2. Interpretivism

Interpretivism focuses on understanding human behaviour by closely examining people’s experiences, interpretations, and perspectives (Bajpai, 2011). The advocates of positivism support the idea of subjectivism. They believe reality is subjective and there are no universal truths (Saunders et al., 2009). This means truth must be created and interpreted subjectively. Individuals must make sense of their own experiences to understand and interpret the world around them. Interpretivism often uses qualitative methods such as interviews, focus groups and observations to collect data (Bajpai, 2011).

1.3. Pragmatism

Pragmatism is a philosophical approach that emphasizes practicality or usefulness as the ultimate criterion for judging truth (Saunders et al., 2009). In other words, pragmatism is committed to using evidence and reason to determine what works best in the real world. It focuses on practical outcomes rather than abstract theories. Pragmatist researchers believe in the efficacy of using practical experience and empirical evidence to determine the truth or falsity of propositions.

The meaning of concepts or ideas cannot be ascertained apart from their use in the context of actual situations. Pragmatism is often contrasted with the epistemological perspective, which holds that knowledge can be derived from a source independent of experience. The following research methods are commonly associated with Pragmatism: empirical observation, experimentation, and survey research.

1.4. Realism

Realism is a philosophical position that believes that the world is fundamentally the same as it is in reality and that the only thing that really matters is what is real. Researchers who adhere to this view believe that there are facts out there that exist independently of human thought or perception. While our perceptions may influence what we observe, ultimately the real world exists outside of our experience or belief. As a result, science can provide us with knowledge about these objective realities (Bajpai, 2011).

Despite the inherent disparities among these philosophical approaches, it’s important to note that one isn’t inherently superior to the others. Instead, researchers may tend to gravitate towards a particular philosophy based on their preferences and the nature of their research (Podsakoff et al., 2012).

2.2. Research Approaches

The second layer of the research onion is the research approach. The onion suggests that a research approach must be selected once the appropriate methodology is chosen. 

According to Saunders et al (2015), there are two main approaches to research: inductive and deductive .

2.1. Inductive research

Inductive research is a type of inquiry that starts with specific observations or experiences and then generalizes them to form theories or hypotheses. The inductive approach is based on interpretivism (Temitope and Udayangani, 2015). This means that the researcher uses his or her personal experiences, observations, and knowledge to form theories that explain the phenomenon being studied. For this reason, inductive research is often considered a more qualitative approach than deductive research.

For example:  suppose you are interested in how people use social media to learn about products. In that case, you might start by collecting data through surveys or interviews, asking people about their experiences buying products online or offline and then draw conclusions based on those interviews. We can see here that the researcher goes from specific to general levels of focus.

As outlined by Bryman and Bell (2011), the inductive approach is predominantly employed in qualitative research. This is particularly advantageous because it obviates the necessity for a guiding theory, which, in turn, diminishes the likelihood of researcher bias during the data gathering phase.

Figure 2 below provides a visual representation of the procedural steps entailed in conducting research utilizing an inductive approach:

2.2. Deductive research

Deductive research starts with a hypothesis or theory that has been established by previous research and then seeks evidence to support or reject it. Here, the researcher goes from general principles to make predictions about what will happen in a specific situation. This approach is based on positivism, i.e. the researcher uses objective methods to gather data from many sources in order to make generalizations about human behavior.

2.3. Research Strategies

2.4. methodological choices, 2.5. time horizons, 2.6. data collection & analysis techniques, common mistakes to avoid.

Nephtali Tshitadi

Nephtali Tshitadi is a researcher and professional content writer with more than 5 years of experience. He holds a Masters's qualification (Mcom) in Finance, Honours Degree in Financial Management, and BCom in Economics.

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• Open access
• Published: 29 November 2022

Growth, yield, and yield variables of onion ( Allium Cepa L.) varieties as influenced by plantspacing at DambiDollo, Western Ethiopia

• Diribsa Alemu 1 ,
• Chala Kitila 1 ,
• Weyessa Garedew 2 ,
• LetaTesfaye Jule 3 , 4 ,
• Bayissa Badassa 5 ,
• N. Nagaprasad 6 ,
• Venkatesh Seenivasan 7 ,
• Abel Saka 3 &
• Krishnaraj Ramaswamy 4 , 8  

Scientific Reports volume  12 , Article number:  20563 ( 2022 ) Cite this article

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• Biological techniques
• Biotechnology
• Engineering
• Plant sciences

Onion ( Allium cepa L.) is an important bulb plant grown worldwide. Proper use of the agronomic practice has undoubtedly contributed to growing crop yields. The right level of any farming practice, like the distance between plants, plant density, date of planting, and time of harvest, can produce the wanted outcomes. Therefore, this research was piloted to evaluate the influence of plant spacing on the development of bulb harvest-related traits of onion varieties in Dambi Dollo University, Western Ethiopia, in 2021. Three onion varieties (Adama red, Monarch, Nafis) and four intra-row spaces (6 cm, 8 cm, 10 cm, and 12 cm) in factorial combinations were settled by a complete randomized block design which was simulated three times. The findings of the study indicate that all the factors related to crop growth and bulb yield of onion varieties were mainly influenced by different kinds and plant spacing. Conversely, the collaboration of these two factors did not affect all other factors, but the interaction of the two factors had a great effect on the days to maturity measured in this study. The highest plant height was registered on the onion planted at a distance of 10 cm (59.83 cm) and 12 cm (59.08 cm) distance between plants. The high commercial yields (34.44 t ha −1 ) and entire bulb yield (35.40 t ha −1 ) were found in the Nafis variety. The highest marketable yields (31.12 ha −1 ) and entire marketable yield (31.78 ha −1 ) were recorded on an onion plant planted 10 cm between plants. Therefore, in the research area, farmers can use a variety of Nafis and a 10 cm distance between plants to increase their onion production.

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Introduction

Onion ( Allium-cepa L.) belongs to the Alliaceae family and the genus Allium 1 , and it is an important crop for bulb plants grown globally. Onions are cultivated for use in a green state and mature bulbs, and some diversity is observed in the eastern Mediterranean countries, which are the main basis of onion genetic variability, as well as they are supposed to be native to onion 2 . Usually, onion is a plant of open, sunny, dry areas, but most species are initiated in cliffs, on waterless foothill slopes, in stony or rocky open areas, or in dry, open, flooded summer plants 1 .

It is essential in the Ethiopian diet daily, which is widely consumed as a spice and or vegetable in strews 3 , and it is the main foundation of flavonoids in human food and the use used to reduce the danger of cancers, temperament diseases, as well as diabetes. The quality parameter of onion as a percentage of single bulbs is essential to encounter the needs of both fresh and processing market buyers 4 .

In Ethiopia, onions are an important economic center due to their easiness of cultivation, more yield per hectare, and the irrigation system increasing onion production from time to time. In Ethiopia, the total area under onion production was about 38,952.58 ha, of which 3,460,480.88 tons were produced in 2020/2021, with an average yield of about 8.8 t ha −1 (CSA, 2021). This showed that the production of onion in Ethiopia (8.8 t ha −1 ) is significantly under the global average (18.8 t ha −1 ). Production of onions can be constrained by unsuitable spacing, deprived fertilization, and inaccessibility of quality planting materials organized with other cultural practices (CSA, 2021).

In Ethiopia, five different kinds of onion (Adama Red, Bombay Red, Red Creole, Melkam, and Nasik Red (Dereselegn) have been released by the research center. The varieties are broadly grown in Ethiopia and Awash Valley, and Lake Region is Bombay Red and Adama Red in larger quantities. However, the adaptive capacity of these varieties is not known in the KellemWollega zone. Proper use of the cultural practice has undoubtedly contributed to growing crop yields. The right farming practice, like planning distance, plant density, and date of planting, time of harvesting, can give the wanted outcomes. The use of recommended plant spacing has two advantages. It evades robust competition among plants through the development influences like marine, nutrients, and sunlight. In contrast, an optimal number of plants allows for the effective use of accessible cropland without waste 6 . In order to improve onion production, information on the appropriate production package is required 5 , 6 .

Appropriate plant spacing allows farmers to retain suitable plant densities in the field. Consequently, it can evade too much or too little in an area that has deleterious influences on the development and profit of onion. The nationally recommended distance between onion plants was 10 cm, grounded on the study conducted in the central rift valley of the country about years ago 6 .

However, producers are complaining about the 10 cm distance between plants producing large bulb sizes that a consumer can choose for home use 7 . As a result, in the real world, the practice accepted by farmers is smaller and/or wider than recommended. Growers in the KellemWollega Zone do not use recommended crop varieties and improved varieties to produce onions, and no new varieties have been introduced locally. In addition, a small amount of research was conducted in the study area to optimize plant spacing and identify better-performing varieties to date. Therefore, onions grown in the study area do not meet the needs of the local market use and people in the study area are forced to buy onions produced in the central part of Ethiopia. Therefore, the present study is designed to identify optimum intra-row spacing that maximizes the onion yield and to evaluate the adaptability of different onion varieties for yield and yield-related trials in the DambiDollo area.

Materials and methodology

Explanation of the study area.

In 2021, research field testing was conducted at the research site of Dambi Dollo University under rain-fed conditions. The pilot investigation was successful. In the western region of Oromia, Ethiopia, in the Kellem Wollega Zone, the research site may be found at an elevation of between 1500 and 1740 m above mean sea level. This location is approximately 652 km distant from Addis Ababa in the westward direction. Annual precipitation averages between 850 and 1200 mm in this region. Temperatures in the region range from a low of 15 degrees Celsius to a high of 28 °C. The soil used in the study was classified as sandy loam 8 .

Descriptions of experimental materials

In this experiment, experimental materials of different varieties of onions obtained from Melkasa Agricultural Research Center (MARC) found in the Eastern part of Oromia, Ethiopia, were used. The different onion varieties used in this experiment were Adama Red, Nafis, and Monarch varieties.

Currently, in Ethiopia, six onion varieties have been released by the Ethiopian Institute of Agricultural Research, viz. Adama Red, Bombay Red, red creole, Memiru Brown, Memiru White, and Nasik Red varieties. Conversely, no varieties were tested in the study area, and there was also no onion seed supply in the study area. The main reasons and causes behind this still have to be further inspected. In Ethiopia in general and in the western part of the country in particular, the monarch is the most grown variety under rain-fed. Farmers and small-scale producers have a preference for a monarch, mainly because it produces well, i.e., a high yield compared to other varieties 6 .

However, farmers prefer the monarch due to its first introduction by traders, and no comparison and study was made to recommend the better onion varieties for the research area. Thus, the varieties like Adama Red, Bombay red, and Nafis were not well known in the study area. Adama red variety was allowed in 1980 by the Federal Research Institute of Ethiopia (Melkasa-Agricultural-Research-center). It is finely modified at an altitude of 1600–2800 m above sea level. Nafis variety was released in 2010. It is well adapted to an elevation of 1600–2800 m above sea level. The monarch is a hybrid variety recently introduced to Ethiopia, and its total bulb yield was 32.76 t ha −1 (Table 1 ). The plant we have used in this report was cultivated in the local area of DambiDollo Town, Oromia, Ethiopia 6 . This study complies with relevant international, national, institutional, and legislative guidelines.

TrialDesign and treatments

The treatments consisted of three varieties of onion (Adama Red, Nafis, and Monarch) and four levels of distance between plants (6 cm, 8 cm, 10 cm, and 12 cm) which were arranged as a complete randomized block design (CRBD) in the factorial arrangement which is duplicated three times. Therefore, a total of 12 combinations of treatments comprised 36 experimental plots, and randomly, each treatment was assigned to the plots. The plot size was 1.8 m by 2 m which is 3.6 m 2 , occupying five rows with 30, 22, 18, and 15 plants on each row for the spacing of 6, 8, 10, and 12 cm, respectively. Each plot consisted of 150 plants for 6 cm, 110 plants for 8 cm, 90 plants for 10 cm, and 75 plants for 12 cm; a distance of 1.0 m was reserved between the blocks, and 0.5 m space was kept between each plot within a block. Exterior lines on both edges of the plots as well as at together edges of row three plants were deliberated (edge plant) to evade border effects.

Experimental procedures

Well-prepared seed beds were sown with seeds, and weeding at the nursery was carried out by hand. The time of sowing the seeds in the investigational beds was made in the 2nd week of April 2021. Before planting the plantlets, the test field was cultivated, sorted, and weighed well. Transplanting was carried out in the first week of May 2021 when they produced 3–4 true leaves (reached a height of 12–15 cm) by cautiously weeding from the nursery seedbed. The seedlings were watered in a nursery one day before the seedlings were transplanted to make it easier to uproot and maintain a good seedling field during replanting. Healthy and uniform seedlings grown in the middle of the seed beds were used for transplanting. Filling of damaged seedlings is done after seven days to substitute those seedlings that failed to establish after planting. Figure  1 (a) shows Seedlings of Onion in the Nursery and (b) Planting of Seedlings on the main field; other recommended agronomic procedures, such as weed control, crop protection, etc., were kept the same throughout treatment.

( a ) Seedlings of onion in the nursery, ( b ) planting of seedlings on the main field.

Data collected

Days to maturity: registered when 90% of the plants in each plant show a collapse of the neck by way of the definite days from transplantation to the time.

Growth parameters

Leaf width or diameter (cm): was registered in 10 casually selected plants per plot, and the average of the longest leaves should be sampled.

The number of leaves/ plants: was recorded when matured from 10 plants per plot.

Plant height (cm): The plant height of 10 casually designated plants on each plot is computed by meters and calculated from the bottom to the top of the leave at ripeness.

Profit and harvest-related traits

Sample plants between three rows were used to record yields and yield-related data. At physiological maturity, when 90% of peaks fell or the leaves withered, the plants were harvested as well as utilized to determine the yield of bulbs and yield-associated parameters 10 . Collected bulbs are cured for a week before topping in the shade (screen house).

Bulb diameter (cm): Bulb diameters were calculated from ten casually nominated onions per plot and were measured using a caliper.

Merchantable bulb’s profit (t ha −1 ): was recognized after dumping splatted bulbs, dense necked, unpleasant bulbs, and commercial new bulbs; profits were calculated from the yield of net plots. The merchantable bulbs harvest weight standard in Ethiopia is categorized as extra-large (beyond 160 g), large (100–160 g), medium (50–85 g), and lesser size(21–50 g) 6 .

Unmarketable bulb yields (t ha −1 ): were decided by classified as: below sized (< 20 g and > 160 g), contaminated, rotten, and disordered physiologically (thick-necked and divided bulbs). These bulbs were weighed and expressed as not commercial bulbs from the net plot area and later extrapolated to a per-hectare basis.

Overall bulb’s harvest (t ha −1 ): The sum of merchantable and marketless bulb yields was computed in tons for each hectare.

Statistical analysis of data

The composed data were exposed to variance examination (ANOVA) in the overall rectilinear model of the Genstat 16 th edition statistical package. The slightestImportant Differences (LSD) at 5% possibility levels were used to associate the conduct rate at which ANOVA showed a significant difference.

Results and discussion

Phenology and growth parameters, times to maturity.

Investigation of variances indicated that days to 90% physiological maturity of the onion varieties were greatly affected (P < 0.001) by the variety and intra-rows space, and their interaction significantly (Fig.  2 ).

Interaction influences diversity and intra rows space on days to physiological maturity.

Maturity dates fluctuated between 121.30 days and 146.00 days. The Adama red variety reached early physiological maturity (121.3 days) at a narrow space of 6 cm, while the Nafis varieties were lately matured (146 days) at a wider space of 12 cm (Fig.  2 ).

The prolonged maturity of onions at the broader distance between plants may be recognized to the low competition for nutrients and light in broader spacing, subsequent comfortable leaf development, and delays in the ripening of bulb 2 . Noted the delayed ripening of onions from sporadically occupied plants and plants grown in closer spacing or in high plant spacing ripe early.

Plant’s height

Plants height was considerably influenced by varieties and intra-rows, and the collaboration of the two influences does not suggestively upset plant height. Decreased crop height in a wide area may be associated with increased competition for growth resources, leading to poor crop yields. And the maximum plant height (61.60 cm) was recorded in the Nafis onion variety. Similarly, the shortest plant height (54.39) was observed from Adama red onion variety Fig.  2 . Likewise 11 , reported Onion Nafisvariety provided the maximum (64.33 cm). Likewise 34 , The highest plant height was obtained in varieties Nafis (10.2 kg).

In another study 12 , documented that the maximum height of plants was observed from the Nafis variety as compared to others. As the distance between plants increases from 7 to 13 cm, the plant height increases. This result is inconsistent with the outcomes of 13 who reported that the longest onion plant was recorded at 15 cm between plants, then plants have grown up through 10 and 7.5 cm.

On the other hand 14 , described that the height of the shallot increased because of the increase in intra-rows space at 20 cm positioning caused by the greatly considerable plant height of the shallot. Consistent with current findings 15 , also reported highest onion height was recorded at a 10 cm spacing between plants at Aksum, northern Ethiopia.

Number of leaves

The number of leaves was suggestively affected by varieties and intra-rows space, and the collaboration of the varieties and intra-rows-space did not affect this parameter. The highest number of leaves (11.47) were recorded at the spacing of 10 cm between plants which is 46.11% more than the lowermost charged documented at an intra-row space of 6 cm (Fig.  2 ).

In another way, the highest number (10.55) was recorded in the Nafis variety, and the plants with the lowest number of leaves (8.840) were recorded in Adama red variety (Fig.  2 ). Likewise 16 , reported that the highest number of leaves were observed in wider plant space 17 . Also showed that as plant population density decreases, the number of leaves produced per plant increases.

Leaf length

Leaf length was suggestively influenced by the foremost effect of plant spacing and varieties. The highest leaf length (54.25 cm) is found in the Nafis variety, and the lowest leaf length comes from Adama red variety (48.77 cm) (Fig.  3 ). The alteration in the length of a leaf between varieties may be due to their genetic differences. Likewise 18 , showed that the highest length of leaf (43.24 cm) from the onion varieties of Nasik Red was linked to other varieties.

The main influence of Varieties and intra-row-space on plants length, leaf number, leaf length, leaf's diameters, and bulb diameters of onion varieties. PH plants length in cm, LN leaf's numbers, LL leaf's length in cm, LD leafs diameters, BD bulb’s diameters, means sharing similar letter(s) are not meaningfully dissimilar at p < 5% bestowing to LSD (least significance difference) test.

The length of the leaf increases as the space between plants is prolonged from 6 to 12 cm. The longest leaves are seen on plants separated at a distance of 10 cm (54.01 cm) and 12 cm (52.54 cm) distance between plants. Although, the plants spaced at 6 cm (49.20 cm) and 8 cm (50.29 cm) showed the minimum length of leaf in Fig.  3 . This may be recognized as the accessibility of extra nutrients and moistness in the wide area between the plants, while the closer distance between plants tends to strong nutrients and moisture competition and thus cause the plant to be shorter 19 , 20 . Reported alike results when the highest leaf length was found in the wide space between plants.

The increase in leaf length of onion varieties in a wide area may be due to suitable distance between plants that allows the leaf to grow robustly and, as a result hence, enhances plant growth. This result is inconsistent with the results of 15 who documented that the highest onion leaf length was found to be 10 cm distance between plants than plants arranged at 5 cm as well as7.5 cm plant space at Aksum, northern Ethiopia. In addition, many researchers have shown that a higher length of a leaf was observed in plants set apart at a broader arrangement 21 , 22 , 23 .

Leaf diameter

Leaf diameter was greatly influenced by intra-rows-space and varieties, whereas the interactions did not show significant results. Increasing the spacing between plants from 6 to 12 cm increases the diameter of the leaf from 1.12 to 1.20 cm (Fig.  3 ). Likewise 11 , reported that as the distance between plants increased, the diameter of the leaf increased.

The width of the broad leaf produced in the wide area of intra-row may be due to the isolated plants receiving the right amount of light that is more imperative for photosynthesis and nutrients associated with distant plants. The highest leaf width is found in plants planted in a wide area between rows compared to a plant planted in close proximity.

Bulb diameter

Bulb diameters of onion plants are strongly affected by the main influence of diversity as well as spacing between plants (P ˂ 0.001), and the interaction of these two factors did not significantly affect bulb diameter.

Variety monarch provided the maximum bulb diameters (5.56 cm). The largest bulb’s diameter (5.50 cm) is found in onion plants planted at a 12 cm distance between plants, followed by plants planted at 8 cm between plants (5.47 cm). Plants separated by 6 cm intra-row provided the lowest bulb diameter (5.33 cm). The plants grown at a spacing of 10 and 12 cm does not show substantial variation between plants grown at 10 and 12 cm.

The increment of bulb diameter in a wide plant spacing may be due to the availability of reserved food nutrients, moisture accessibility, and causing an expansion in bulb size. Likewise, a great plant population indicates the nearer proximity and final decrease of available area per plant, and then it is true that enlargement of the bulb may be inadequate due to reduced planting space 24 . The current findings are consistent with 25 who obtained the maximum bulb diameter from wider intra-row spacing). Likewise 11 , reported that the maximum diameter of the bulb (5.63 cm) was recorded at a 13 cm distance between plants.

Yield and yield components

Marketable yield.

Marketable bulb’s yields were suggestively (P ˂ 0.001) affected by variety as well as space, while the interface didn’t influence marketable bulb yield. The Nafis varieties have yielded the uppermost commercial bulb’s yield (34.44 t ha −1 ), followed by varieties monarch (31.45 t ha −1 ), and the lowermost commercial bulb’s yields (21.74 t ha −1 ) were gained from varieties of Adama red (Table 2 ). Likewise 34 , the highest marketable bulb yield per plot, was attained in diversities Nafis (10.2 kg).

The differences observed between onion varieties may be attributed to the ability to work under different agricultural climatic conditions and genetic makeup. Consistent with the present result 12 , stated the higher and lower yield of the bulb (15.94 t ha −1 and 9.17 t ha −1 ) from diversityNafisas well as Adama Red separately. The highest commercial yield of the bulb (31.12 t ha −1 ) was recorded on 10 cm planted crops, and the lowermost saleable bulb yield (27.17 t ha −1 ) was observed on 6 cm planted crops Table 2 .

The size of the bulb under a wider space did not recompense for the decrease in yield per hectare initiated by a decrease in the number of plants in the wider space 29 . Plant density affects the marketable bulb yield, and the high plant population results in reduced marketable bulb size. The higher yields of commercial yields in the smallest distance between plants may be owed to more plant density, producing more bulb yields 26 . Obtained the uppermost commercial yields (34.49 t ha −1 ) from the nearby space (5 cm). Russo (2008) also showed that 97% of marketable bulbs of onion are from a closely occupied plant. The result is inconsistent with those of 16 who documented that surpassed bulbs of Huruta shallot implanted at a 10 cm distance between plants gave the highest yield per hectare compared to 15 and 20 cm spacing 15 . Likewise stated, an increase in the distance between plants from 5 to 10 cm reduced merchantable bulb’s yields from 34.49 to 28.10 t ha −1 19 . Also found a reduced yield of marketable bulb yield as the space between the plant's increases from 5 to 10 cm. In contrast, the yield of shallot was high at broader intra-row-space (20 and 25 cm) as compared to 15 cm spacing 27 .

Unmarketable bulb’s yields

Unmarketable bulb’s yields were significantly (P < 0.001) affected by variety and intra-row- space, while the interaction did not affect unmarketable bulb yield. The maximum yield of an unmarketable bulb (1.93 t ha −1 ) was observed on a plant planted in a narrow space (6 cm) and wider (12 cm) spacing (Table 2 ).

The highest unmarketable yield in a narrow space may be related to increased rivalry for growing assets and a lack of nutrients for the progress and expansion of all plants in the stand. The lesser non-marketable yields in greater spacing may be due to the limited opposition for growth resources leading to large segments that increase the yield of the unmarketable bulb.

This may be particularly noted in the case of nitrogen deficiency and poor plant growth, leading to weaken plants' susceptibility to other biotic and abiotic pressure and assimilate production, leading to reduced bulb size 21 , 22 , 23 . Also showed that the control treatment yielded a high unmarketable yield, while low non-marketable yields were related to high nitrogen levels.

The highest non-marketable yields in the closest spacing may be due to competition between plants and growth-promoting resources, which has led to a much lesser level of big bulbs than wider spacing. In addition, it may be due to poor nutrition, light, and space in dense vegetation. The results are concomitant with 9 and 16 , who noted that the space between the narrow spacing increases the yield of unmarketable bulbs of onion and shallot, respectively.In contrast 28 , documented that wider spacing yielded maximum unmarketable yield due to higher bulb diameter that resulted in an oversize bulb and consequently higher unmarketable yield.

Total bulb yield

The total bulb’s yields were expressively (P ˂ 0.001) affected by varieties as well as intra-row -spaces, while the influence of the interaction was not. The maximum yields of bulbs (35.40 t ha −1 ) are attained from the Nafisvariety followed by a monarch (32.76 t ha −1 ), while the lowermost bulb yield (22.92 t ha −1 ) was observed in the diversity Adama Red (Table 2 ).

Differences in the production of bulbs are contingent on the difference in cultivars, agroecology, agronomic applications, and their relations. The outcome is concomitant with the findings of 12 who initiated Nafis variety gave the maximum total bulb yield than other varieties.

In addition, the maximum amount of marketable yield (31.78 t ha −1 ) and the minimum commercial yield (29.10 t ha −1 ) was attained in the closest (6 cm) and widest (10 cm) distance between plants correspondingly. The increase in the total yields of bulbs by a high number of plants may be due to the increase in plant stand and, as a result, the advanced bulb number formed in each area. Conversely, the weights of the bulb are decreased because of high opposition between plants for development influences. Likewise 25 , reported higher yields of total bulbs from onion crops that have more populations than those planted less.

Therefore, using a 10 cm spacing is an excellent dose of onion for commercial and produces a better bulb yield. Similarly, Refs. 29 , 30 , 31 , 32 , 33 , 34 , 35 reported that an increase in bulb yield is due to increased nitrogen consumption. Al-Frahat (2009) also pointed out that the 0 NPS applied plots recorded inferior yield as associated with the greater nitrogen dose. Likewise 14 , reported that the Nitrogen level increase from 100 to 150 kg ha −1 didn’t raise yields.

Moreover, this finding is similar to the discoveries of 36 , 37 , 38 , 39 , who described that proliferation in the distance between shallots plants from 5 to 20 cm occasioned a decrease in yields from 36.0 t ha −1 to 23.9 t ha −1 but most (86%) of the bulbs was very low and therefore could not be unmarketable at 5 cm intra-rows- space. Likewise 16 , found that the amount of total yield reduced with the rise in the intra-row-space of shallot.

Conclusion and recommendations

In conclusion, the major impact of the variety of onions and intra-row spacing greatly affects all phenological growth variables and yields contributing traits of onion crops. The variance of analysis displayed that except for days to 90% physiological mellowness, which is affected by the interactions influences of variety and intra-rows-spacing, altogether, constraints are greatly affected by the variety and distance between plants.

From this finding, the highest yield of the marketable bulb (31.12 t ha −1 ) of onion was recorded on 10 cm planted crops for intra-raw spacing, and low yields of the marketable bulb (27.17 t ha −1 ) are noted on plants planted at 6 cm intra row spacing. Additionally, the maximum commercial yield (34.44 t ha −1 ) was noted from the variety Nafis, and the lowest value (21.74 t ha −1 ) was documented from Adama red variety. Considering the main influences of space, the maximum yield of an unmarketable bulb (1.93 t ha −1 ) was documented in plants with a small intra-raw space, and the lowest value (0.66 t ha −1 ) was documented in plants with 10 cm intra-raw-space. And the maximum non-marketable yield (1.18 t ha −1 ) was noted from Adama red variety, and the lowermost unmarketable yield (0.96 t ha −1 ) was observed from the Nafis varieties. Thus, it is conceivable to decide that 10 cm intra-row-spacing, as well as the varieties of Nafis, will be used for the production of onions at the research site. Nevertheless, this study was conducted only one season in one place; therefore, the same research should be done under different agro-climate and soil conditions in order to make a complete recommendation.

Data availability

The datasets used and analyzed during the current study are available from the corresponding author on request.

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Conceptualization, D.A., C.K., W.G., L.T.J., B.B., N.N., A.S. and K.R.; data curation, D.A., C.K., W.G., L.T.J., B.B., N.N., A.S., V.S. and K.R.; analysis and validation, D.A., C.K., W.G., L.T.J., B.B., N.N., A.S. and K.R.; formal analysis, L.T.J., V.S., B.B., N.N., A.S. and K.R.; investigation, D.A., C.K., W.G., L.T.J., B.B., N.N., A.S. and K.R.; methodology, D.A., C.K., W.G., L.T.J., B.B., N.N., A.S., V.S. and K.R.; project administration, L.T.J., and K.R. Resources, D.A., C.K., W.G., L.T.J., B.B., A.S.K.R.; software, D.A., C.K., W.G., L.T.J., B.B., N.N., A.S. and K.R., supervision, K.R. and L.T.J.; validation, D.A., C.K., W.G., L.T.J., B.B., N.N. and K.R.; visualization, D.A., C.K., W.G., L.T.J., B.B., N.N., A.S., V.S. and K.R.; Writing—original draft, D.A., C.K., W.G., L.T.J., B.B., N.N., A.S. and K.R., data visualization, editing and rewriting, D.A., C.K., W.G., L.T.J., B.B., N.N., A.S. and K.R.

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Alemu, D., Kitila, C., Garedew, W. et al. Growth, yield, and yield variables of onion ( Allium Cepa L.) varieties as influenced by plantspacing at DambiDollo, Western Ethiopia. Sci Rep 12 , 20563 (2022). https://doi.org/10.1038/s41598-022-24993-x

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The research onion for beginners

Disclaimer: Some posts on Tourism Teacher may contain affiliate links. If you appreciate this content, you can show your support by making a purchase through these links or by buying me a coffee . Thank you for your support!

Today I will explain the research onion in simple terms. This builds on from my last post, where I introduced you to the concept of research philosophy , giving the simple analogy of a tree which demonstrated how philosophy is inherently linked to research design. 

What is the research onion?

Layers of the research onion, research philosophy, research approach, research strategy, time horizons, data collection and analysis.

The research onion was developed by Saunders et al in 2007 to describe the stages through which a researcher must pass when developing an effective methodology. Just as I previously explained, in order for your research to have maximum credibility, you must provide explanations and justifications for each level of your methodological decisions. The research onion is basically an extension of the research methods tree.

As you can guess, there are different layers to the research onion – the premise being that you start from the outside and peel each layer away until you reach the core. These layers are broken up into six main areas: research philosophy; research approach; research strategy; research choices; time horizons; and techniques and procedures. I will explain what each layer means below.

Research philosophy refers to the set of beliefs concerning the nature of the reality being investigated. It is generally examined in terms of ontology and epistemology. I have provided more detail on this in my post- ‘ Ontology and Epistemology: A Simple Explanation ’, but for now I will provide a brief description of each as follows:

• Epistemology: What Constitutes Valid Knowledge and How Can We Obtain It?
• Ontology: What Constitutes Reality and How Can We Understand Existence?

There are two main positions considered here, known as positivism and interpretivism. This underpins the qualitative versus quantitative debate, often referred to as “the scientist versus detective” debate. I explain exactly what all of this means in my post- ‘ Positivism and Interpretivism: A Simple Explanation ’.

This is referring to the approach that the researcher takes, which can largely be described as either inductive or deductive.

The deductive approach starts small and gets bigger. It starts with a specific hypothesis or hypotheses that have been developed based on information or patterns that have been observed by the researcher. It then seeks to test this hypothesis and develop a broader theory from it.

The inductive approach is the opposite. It starts with a broad theory and then focuses later on the smaller, more specific details. This is sometimes referred to as a move from the specific to the general.

Typically, a deductive approach is associated with quantitative research and an inductive approach is associated with qualitative research.

There are some great texts on this, which will give you a more detailed explanation. One of my favourites is ‘ Key Concepts in the Philosophy of Social Research’ by Malcolm Williams , which I used a lot when writing my PhD thesis. 

The strategy layer of the research onion refers to how the researcher intends to carry out the work, i.e. what method of data collection will be used. You can read more about research method strategies in Cresswell’s book ‘ Research Design: Qualitative, Quantitative, and Mixed Methods Approaches ‘ .

The choices outlined in the research onion include the mono method, the mixed method, and the multi-method.

The mono-method involves using one research approach for the study. Next, the mixed-methods required the use of two or more methods of research, and usually refers to the use of both a qualitative and a quantitative methodology. In the multi-method, a wider selection of methods is used. You can also read more about the use of mixed methods research in Cresswell’s text , which is personally one of my favourites- it’s easy to understand and provides detailed explanations. 

The Time Horizon refers to the time frame within which the project is intended for completion. According to the research onion, there are two types of time horizons: cross-sectional and longitudinal.

The cross-sectional time horizon is when there is a pre-set time established for the collection of data. A longitudinal time horizon refers to the collection of data repeatedly over an extended period, for example when a person reaches a different age or different seasons throughout the year.

The final layer of the research onion is techniques and procedures. This is the section where you should make explicit exactly how and why you are undertaking the research.

This can be referring to primary data (data collected first-hand for the research project), or secondary data (data that was collected by somebody else and subsequently published).

You will need to make your research design clear, with valid justifications for each stage. This provides a framework that includes the considerations that led to the appropriate methodology being adopted, the way in which the respondents were selected, and how the data will be analysed.

You will also cover research samples in this inner layer of the research onion. A sample is a representative segment of a larger population . In this instance, it is referring to the people who participated in your study. You will need to explain who was selected and why, supported by sampling theory, which you will find in most research methods textbooks. The reader will also want to know about your sample size.

Lastly, it is worthwhile addressing the ethics of your research in this last section of the research onion. This demonstrates that you have been an ethical researcher and that you comply with any regulations set upon you by your university. 

So, that sums up the research onion. And in actual fact it sums up your overall methodology chapter for your research project! I have a number of posts covering each of the areas mentioned in the research onion further, so read on should you require further guidance. I also recommend that you use some of the excellent research methods books available to you- I recommend Social Research Methods by Bryman and Research Methodology: A Step by Step Guide for Beginners by Kumar .

Lastly, I have also included a handy YouTube video below that explains the research onion very clearly (I’ll get round to making my own one day).

If you wish to cite any of the content in the post please reference ‘Stainton, Hayley. (2018) Lifeasabutterfly.’

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Understanding Research Onion for Research Methodology

Research onion is a framework for developing different types of research methodology, depending upon the objective of the study. Research onion was developed by Saunders et al (2007) in their book “Research Method for Business Students”. The model consists of multiple layers that are arranged in a way similar to the layers of an onion.

Research Onion Methodology Examples

The outermost layer represents four types of research philosophies that include positivism , interpretivism , pragmatism , and realism  (Saunders, 2007) .  The first decision is to choose a research philosophy to develop foundation of the overall research methodology.

Quantitative Research

The purpose of quantitative research is to understand patterns, causes, and relationship between different variables. Quantitative research is actually positivist research that aims to validate hypothesis derived from existing theories. Such studies are based on deductive reasoning approach. These studies intend to test existing theories by utilizing a specific dataset collected from samples. Explanatory research  is a type of investigation used in quantitative research to explain statistical relationship between variables within the scope of the study (Seakran, 2003). Monomethod quantitative research uses only one method to gather data from sources and performing analysis of data.

Also Read: Time Horizon in Research onion

Qualitative Research

Qualitative research aims to understand different process, subject, or phenomenon. Interpretivist studies are qualitative research aiming to develop a deeper understanding of the underlying phenomenon. E thnographic research, phenomenological research, case study, grounded theory , and action theory  are different types of qualitative research. The purpose of inductive reasoning is to develop theories using organized observation and analysis of observations. In these studies, researchers do not use hypothesis testing to test existing theories but rather focus on developing new theories.

Mixed Research

Mixed research is a combination of qualitative and quantitative research. Pragmatism enables researchers to develop research methodology that can address the research objectives and problem statement effectively. Pragmatism is flexible and not based on limitations of qualitative and quantitative research. Mixed research integrates advantages of qualitative and quantitative research within a single study to overcome their respective limitations. Such research is sequential that understands a phenomenon and tests the hypothesis derived from findings of the study.Researchers use the sequential approach of employing inductive and deductive reasoning in such studies (Creswell, 2007).

Creswell. (2007). Research Design- Qualitative and mixed methods approaches.  London: Sage Publishers. Saunders, M. L. (2007). Research methods for business students  (5th ed.). Essex: Pearson Education Limited. Seakran, U. (2003). Research Methods for Business.  United States: John Wiley and Sons. Retrieved from https://iaear.weebly.com/uploads/2/6/2/5/26257106/research_methods_entiree_book_umasekaram-pdf-130527124352-phpapp02.pdf

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CENTRAL ASIA BLOG: Cautionary tale as onion prices crash amid glut on a "tragic" scale

By Tawney Kruger in Tashkent

If you’ve an appetite for lashings and lashings of French onion soup then Uzbekistan is the place to be right now. According to trade experts , you can buy one kilogram of onions for as little as $0.12.

Estimates suggest that due to what the trade news and analysis site EastFruit refers to as “tragic onion overproduction”, somewhere between 150,000-200,000 tonnes of onions may end up being discarded or used as cattle feed in Uzbekistan. A similar story is playing out in Kazakhstan and other parts of Central Asia. It’s a desperate situation for farmers and a cautionary tale.

The stark price drop means that for $100 you could be the proud owner of 830 kilograms of onions. In 2023, onion prices were 4.4 times higher in Uzbekistan at $0.52 per kilogram.

Reports last year suggested that a rush to increase the volume of onion farming was in part triggered by false rumours on Telegram about onion prices set to shoot up due to restrictions on onion exports from India.

For those who invested in onions last autumn with the intent of profiting from big sales in the spring, the market crash has been devastating. With prices plummeting towards zero, selling off the 2023/2024 harvest is proving nearly impossible.

Andriy Yarmak, an economist at the Food and Agriculture Organisation (FAO), pointed out to EastFruit that onion demand in Central Asia does not change much in response to price shifts. That’s because consumers in the region typically use onions as ingredients or garnishes, rather than as the dominant ingredient in main dishes. Central Asians have no reason to purchase onions in significantly larger quantities than usual despite the bargain prices on offer.

While the onion farmers frown, or perhaps dissolve in tears, the market experts at Eastfruit can claim a painful analytical victory. Last year, they forewarned that the onion overproduction evident in Uzbekistan would lead to a yield expansion of up to 40% and a 400,000-tonne surplus of onions from the 2023/2024 onion-growing and harvesting.

One might say that the dreamt of boom in onion profits chased by the farmers proved to be something like a magical onion in a fairy tale that offered riches: they peeled off layer after layer, only to find there was no treasure within.