7/10/2023 0 Comments Cohort studies![]() Therefore, cohort studies are good for assessing prognosis, risk factors and harm. See Figure 2 for a pictorial representation of a cohort study design. The study then follows these participants for a defined period to assess the proportion that develop the outcome/disease of interest. 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. ![]() This is one of their important strengths. People are recruited into cohort studies regardless of their exposure or outcome status. Prospective cohort studies are more common. 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. In retrospective cohort studies, the exposure and outcomes have already happened. Retrospective cohort studies are NOT the same as case-control studies. ![]() Cohort studiesĬohort studies can be retrospective or prospective. Advantages and disadvantages of case-control studies. 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.Ī summary of the pros and cons of case-control studies are provided in Table 1. Recall bias is the systematic difference in how the two groups may recall past events e.g. Often case-control studies require the participants to self-report their exposure to a certain factor. Nevertheless, as case-controls are retrospective, they are more prone to bias. Furthermore, you can assess multiple exposures to get a better understanding of possible risk factors for the defined outcome / disease. The fact that the analysis is retrospective, allows rare diseases or diseases with long latency periods to be investigated. It may even increase statistical power and study precision by choosing up to three or four controls per case (2).Ĭase-controls can provide fast results and they are cheaper to perform than most other studies. age, sex) to ensure these do not confound the study results. It is possible to match controls to the cases selected on the basis of various factors (e.g. Regardless of how the cases are selected, they should be representative of the broader disease population that you are investigating to ensure generalisability.Ĭase-control studies should include two groups that are identical EXCEPT for their outcome / disease status.Īs such, controls should also be selected carefully. 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. The main outcome measure in case-control studies is odds ratio (OR).Ĭases should be selected based on objective inclusion and exclusion criteria from a reliable source such as a disease registry. This can suggest associations between the risk factor and development of the disease in question, although no definitive causality can be drawn. See Figure 1 for a pictorial representation of a case-control study design. 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. ![]() They clearly define two groups at the start: one with the outcome/disease and one without the outcome/disease. Case-control studiesĬase-control studies are retrospective. Although these studies are not ranked as highly as randomised controlled trials, they can provide strong evidence if designed appropriately. These types of studies, along with randomised controlled trials, constitute analytical studies, whereas case reports and case series define descriptive studies (1). Case-control and cohort studies are observational studies that lie near the middle of the hierarchy of evidence.
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