case control studies of disease

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Journal of Epidemiology
Volume 1 (1991) Issue 1
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Department of Hygiene and Preventive Medicine, Niigata University School of Medicine

Department ofPublic Health, Jichi Medical School

Department of Public Health, Akita University School of Medicine

Department of Public Health Care Informatics Suzuka University of Medical Science and Technology

Sano Public Health Center

Department of Health and Welfare

Takahagi PublicHealth Center

Department of Health and Environmental Protection

Department of Healthand Environmental Protection

Department of Public Health, Tottori University School of Medicine

Department of Hygiene, Gifu University School of Medicine

Department of Hygiene, ShowaUniversity School of Medicine

Department of Public Health, Wakayama Medical College

Corresponding author

1991 Volume 1 Issue 1 Pages 19-25

Published: 1991 Received: September 19, 1991 Available on J-STAGE: November 30, 2007 Accepted: October 02, 1991 Advance online publication: - Revised: -

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A nation-wide case-control study was conducted to identify the risk factors and to give clues to the etiology of Buerger's disease. Cases were 153 male patients who were the receivers of national financial aids for the treatment of the disease and were enrolled in public health center. For each case, a control was randomly selected from the list of the examinees of health examinations in the public health center same as the case and was matched to the case by age (± 5 years old) and sex. Self-administered questionnaires were mailed to all study participants. The results of statistical analyses under the condition that the estimated onset age of the case was under 50 years old were as follows ; (1) strong link between tobacco and Buerger's disease was statistically reconfirmed. (2) cases consumed a less amount of milk than controls. (3) cases were engaged in physical works more frequently and under noisier and dustier environments than controls. (4) the past history of allergic rhinitis was found more on the side of cases. J Epidemiol, 1991; 1 : 19-25.

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Case-control and Cohort studies: A brief overview

Posted on 6th December 2017 by Saul Crandon

Introduction

Case-control and cohort studies are observational studies that lie near the middle of the hierarchy of evidence . These types of studies, along with randomised controlled trials, constitute analytical studies, whereas case reports and case series define descriptive studies (1). Although these studies are not ranked as highly as randomised controlled trials, they can provide strong evidence if designed appropriately.

Case-control studies

Case-control studies are retrospective. They clearly define two groups at the start: one with the outcome/disease and one without the outcome/disease. They look back to assess whether there is a statistically significant difference in the rates of exposure to a defined risk factor between the groups. See Figure 1 for a pictorial representation of a case-control study design. This can suggest associations between the risk factor and development of the disease in question, although no definitive causality can be drawn. The main outcome measure in case-control studies is odds ratio (OR) .

Figure 1. Case-control study design.

Cases should be selected based on objective inclusion and exclusion criteria from a reliable source such as a disease registry. An inherent issue with selecting cases is that a certain proportion of those with the disease would not have a formal diagnosis, may not present for medical care, may be misdiagnosed or may have died before getting a diagnosis. Regardless of how the cases are selected, they should be representative of the broader disease population that you are investigating to ensure generalisability.

Case-control studies should include two groups that are identical EXCEPT for their outcome / disease status.

As such, controls should also be selected carefully. It is possible to match controls to the cases selected on the basis of various factors (e.g. age, sex) to ensure these do not confound the study results. It may even increase statistical power and study precision by choosing up to three or four controls per case (2).

Case-controls can provide fast results and they are cheaper to perform than most other studies. The fact that the analysis is retrospective, allows rare diseases or diseases with long latency periods to be investigated. Furthermore, you can assess multiple exposures to get a better understanding of possible risk factors for the defined outcome / disease.

Nevertheless, as case-controls are retrospective, they are more prone to bias. One of the main examples is recall bias. Often case-control studies require the participants to self-report their exposure to a certain factor. Recall bias is the systematic difference in how the two groups may recall past events e.g. in a study investigating stillbirth, a mother who experienced this may recall the possible contributing factors a lot more vividly than a mother who had a healthy birth.

A summary of the pros and cons of case-control studies are provided in Table 1.

Table 1. Advantages and disadvantages of case-control studies.

Cohort studies

Cohort studies can be retrospective or prospective. Retrospective cohort studies are NOT the same as case-control studies.

In retrospective cohort studies, the exposure and outcomes have already happened. They are usually conducted on data that already exists (from prospective studies) and the exposures are defined before looking at the existing outcome data to see whether exposure to a risk factor is associated with a statistically significant difference in the outcome development rate.

Prospective cohort studies are more common. People are recruited into cohort studies regardless of their exposure or outcome status. This is one of their important strengths. People are often recruited because of their geographical area or occupation, for example, and researchers can then measure and analyse a range of exposures and outcomes.

The study then follows these participants for a defined period to assess the proportion that develop the outcome/disease of interest. See Figure 2 for a pictorial representation of a cohort study design. Therefore, cohort studies are good for assessing prognosis, risk factors and harm. The outcome measure in cohort studies is usually a risk ratio / relative risk (RR).

Figure 2. Cohort study design.

Cohort studies should include two groups that are identical EXCEPT for their exposure status.

As a result, both exposed and unexposed groups should be recruited from the same source population. Another important consideration is attrition. If a significant number of participants are not followed up (lost, death, dropped out) then this may impact the validity of the study. Not only does it decrease the study’s power, but there may be attrition bias – a significant difference between the groups of those that did not complete the study.

Cohort studies can assess a range of outcomes allowing an exposure to be rigorously assessed for its impact in developing disease. Additionally, they are good for rare exposures, e.g. contact with a chemical radiation blast.

Whilst cohort studies are useful, they can be expensive and time-consuming, especially if a long follow-up period is chosen or the disease itself is rare or has a long latency.

A summary of the pros and cons of cohort studies are provided in Table 2.

The Strengthening of Reporting of Observational Studies in Epidemiology Statement (STROBE)

STROBE provides a checklist of important steps for conducting these types of studies, as well as acting as best-practice reporting guidelines (3). Both case-control and cohort studies are observational, with varying advantages and disadvantages. However, the most important factor to the quality of evidence these studies provide, is their methodological quality.

Saul Crandon

No Comments on Case-control and Cohort studies: A brief overview

Very well presented, excellent clarifications. Has put me right back into class, literally!

Very clear and informative! Thank you.

very informative article.

Thank you for the easy to understand blog in cohort studies. I want to follow a group of people with and without a disease to see what health outcomes occurs to them in future such as hospitalisations, diagnoses, procedures etc, as I have many health outcomes to consider, my questions is how to make sure these outcomes has not occurred before the “exposure disease”. As, in cohort studies we are looking at incidence (new) cases, so if an outcome have occurred before the exposure, I can leave them out of the analysis. But because I am not looking at a single outcome which can be checked easily and if happened before exposure can be left out. I have EHR data, so all the exposure and outcome have occurred. my aim is to check the rates of different health outcomes between the exposed)dementia) and unexposed(non-dementia) individuals.

Very helpful information

Thanks for making this subject student friendly and easier to understand. A great help.

Thanks a lot. It really helped me to understand the topic. I am taking epidemiology class this winter, and your paper really saved me.

Happy new year.

Wow its amazing n simple way of briefing ,which i was enjoyed to learn this.its very easy n quick to pick ideas .. Thanks n stay connected

Saul you absolute melt! Really good work man

am a student of public health. This information is simple and well presented to the point. Thank you so much.

very helpful information provided here

really thanks for wonderful information because i doing my bachelor degree research by survival model

Quite informative thank you so much for the info please continue posting. An mph student with Africa university Zimbabwe.

Thank you this was so helpful amazing

Apreciated the information provided above.

So clear and perfect. The language is simple and superb.I am recommending this to all budding epidemiology students. Thanks a lot.

Great to hear, thank you AJ!

I have recently completed an investigational study where evidence of phlebitis was determined in a control cohort by data mining from electronic medical records. We then introduced an intervention in an attempt to reduce incidence of phlebitis in a second cohort. Again, results were determined by data mining. This was an expedited study, so there subjects were enrolled in a specific cohort based on date(s) of the drug infused. How do I define this study? Thanks so much.

thanks for the information and knowledge about observational studies. am a masters student in public health/epidemilogy of the faculty of medicines and pharmaceutical sciences , University of Dschang. this information is very explicit and straight to the point

Very much helpful

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International Journal of Pediatrics

Indexing and Abstracting

The Relationship between Periodontal Disease, Preterm Delivery, and Low Birth Weight of Infants: A Case-Control Study

Document Type : original article

1 Department of Oral & Maxillofacial Diseases, School of Dentistry, Infectious Diseases Research Center, Birjand University of Medical Sciences, Birjand, Iran.

2 Assistant Professor of Periodontology, Department of Periodontics, School of Dentistry, Birjand University of Medical Sciences, Birjand, Iran

3 Birjand University of Medical Sciences, Birjand, Iran.

4 Department of Gynecology, School of Medicine, Birjand University of Medical Sciences, Birjand, Iran.

5 Assistant Professor of Epidemiology, Department of Epidemiology and Biostatistics, School of Health Social Determinants of Health Research Center Birjand University of Medical Sciences, Birjand, Iran.

Background: Periodontal diseases, causing an infection site in the body, may be associated with a wide array of local and systemic diseases and conditions. Due to the high prevalence of periodontal disease in women, this study was conducted with the aim of determining whether periodontal disease during pregnancy is associated with premature delivery and low birth weight of the infants. Methods: In this case-control study, the presence of periodontal disease in 115 mothers with premature birth (before 37 weeks) who had babies weighing less than 2500 grams were compared to 115 mothers with term births (after 37 weeks) and babies weighing over 2500 grams referred to the maternity hospital of Vali-e-Asr Birjand Educational-Therapeutic Center. Periodontal pocket depth, CPITN index, and gingival index were measured for 6 teeth with Ramfjord index. Data analysis was done using SPSS 16 software. The findings were described with mean ± standard deviation and frequency distribution tables; in addition, a comparison between the two groups was made with chi-square and independent t-test. Results: There was no difference between the two groups in terms of demographic variables. The average depth of the periodontal pocket, gingival index, as well as the index of severity and extent of periodontal disease in the case group were much higher than in the control group and these differences were statistically significant (P<0.05). Conclusion: Periodontal diseases during pregnancy increase the risk of giving birth to a premature and low birth weight baby. Therefore, it is recommended to pay more attention to the examination and treatment of periodontal diseases in pre-pregnancy care and during pregnancy.

Cekici A, Kantarci A, Hasturk H, Van Dyke TE. Inflammatory and immune pathways in the pathogenesis of periodontal disease. Periodontol 2000. 2014; 64(1):57-80.

Volume 11, Issue 4 April 2023 Pages 17665-17672

Akbari, N., Keyvanfar, S., Hajipour, E., Ghanbarzadeh, N., & Salehiniya, H. (2023). The Relationship between Periodontal Disease, Preterm Delivery, and Low Birth Weight of Infants: A Case-Control Study. International Journal of Pediatrics , 11 (4), 17665-17672. doi: 10.22038/ijp.2023.69847.5150

Narjes Akbari; Sanaz Keyvanfar; Elahe Hajipour; Nahid Ghanbarzadeh; Hamid Salehiniya. "The Relationship between Periodontal Disease, Preterm Delivery, and Low Birth Weight of Infants: A Case-Control Study". International Journal of Pediatrics , 11, 4, 2023, 17665-17672. doi: 10.22038/ijp.2023.69847.5150

Akbari, N., Keyvanfar, S., Hajipour, E., Ghanbarzadeh, N., Salehiniya, H. (2023). 'The Relationship between Periodontal Disease, Preterm Delivery, and Low Birth Weight of Infants: A Case-Control Study', International Journal of Pediatrics , 11(4), pp. 17665-17672. doi: 10.22038/ijp.2023.69847.5150

Akbari, N., Keyvanfar, S., Hajipour, E., Ghanbarzadeh, N., Salehiniya, H. The Relationship between Periodontal Disease, Preterm Delivery, and Low Birth Weight of Infants: A Case-Control Study. International Journal of Pediatrics , 2023; 11(4): 17665-17672. doi: 10.22038/ijp.2023.69847.5150

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