When is it Desirable to Conduct a Case-Control Study?
Case-control studies provide a method that avoids many of the limitations of cohort studies. Case-control studies are advantageous under the following circumstances:
- When exposure data are expensive or difficult to obtain, e.g., assessing pesticide levels in blood or other medical tests
- When the disease has a long induction and/or latent period, e.g., cancer, dementia. With a case-control study one does not have to wait for disease to occur,
- When the outcome (disease) is rare. (A cohort study would require too large a sample size, e.g., when studying rare parasitic diseases.)
- When the study population is dynamic and it is difficult to maintain follow up, e.g., a homeless population
- When little is known about a disease, case-control studie can evaluate multiple exposures, e.g., in the early studies of AIDS.
Advantages and Disadvantages of Case-Control Studies
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Strengths of Case-Control Studies:
The temporal sequence between exposure and outcome is generally clear (but not always). There are fewer ethical concerns than in randomized clinical trials. They are less expensive and time-consuming than prospective cohort studies. They are more efficient for rare outcomes and diseases with long latency between exposure and development of the outcome. They are more efficient when exposure data is difficult or costly to obtain. They are good for studying dynamic populations in which follow up is difficult. They can evaluate effects of multiple exposures on single outcome.
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Limitations of Case-Control Studies: They focus on a single outcome. They are Inefficient for rare exposures. Information on past exposures may be inaccurate, especially if obtained by recollection of the subjects. They are more susceptible to selection bias, recall bias, and interviewer bias (discussed in the module on Bias). Do not allow calculation of incidence, risk ratio, or risk difference.
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