The most commonly cited disadvantage in case-control studies is the potential for recall bias. In a case-control study, the investigator can include unequal numbers of cases with controls such as 2:1 or 4:1 to increase the power of the study. This study mechanism can be commonly seen in food-related disease outbreaks associated with contaminated products, or when rare diseases start to increase in frequency, as has been seen with measles in recent years.īecause of these advantages, case-control studies are commonly used as one of the first studies to build evidence of an association between exposure and an event or disease. In the example above about Kaposi's sarcoma, the researcher could ask both the cases and controls about exposures to HIV, asbestos, smoking, lead, sunburns, aniline dye, alcohol, herpes, human papillomavirus, or any number of possible exposures to identify those most likely associated with Kaposi's sarcoma.Ĭase-control studies can also be very helpful when disease outbreaks occur, and potential links and exposures need to be identified. Second, the case-control study design makes it possible to look at multiple risk factors at once. As it may be impractical to follow 1,000,000 for ten years or to wait 1000 years for recruitment, a case-control study allows for a more feasible approach. If the disease is much rarer, say 1 in 1,000,0000 per year (0.0000001/year) this would require either having to follow 1,000,0000 people for ten years or 1000 people for 1000 years to accrue ten total cases. For example, if a disease developed in 1 in 1000 people per year (0.001/year) then in ten years one would expect about 10 cases of a disease to exist in a group of 1000 people. Such use of resources may be impractical, so a case-control study can be useful for identifying current cases and evaluating historical associated factors. If a disease occurs very infrequently, one would have to follow a large group of people for a long period of time to accrue enough incident cases to study. First, the case-control approach allows for the study of rare diseases. There are many advantages to case-control studies. The researcher might find that those with Kaposi's sarcoma are more likely to have HIV, and thus conclude that HIV may be a risk factor for the development of Kaposi's sarcoma. The researcher could then ask about various exposures to see if any exposure is more common in those with Kaposi's sarcoma (the cases) than those without Kaposi's sarcoma (the controls). The researcher would find a group of individuals with Kaposi's sarcoma (the cases) and compare them to a group of patients who are similar to the cases in most ways but do not have Kaposi's sarcoma (controls). If the exposure is found more commonly in the cases than in the controls, the researcher can hypothesize that the exposure may be linked to the outcome of interest.įor example, a researcher may want to look at the rare cancer Kaposi's sarcoma. The researcher then looks at historical factors to identify if some exposure(s) is/are found more commonly in the cases than the controls. The researcher then tries to construct a second group of individuals called the controls, who are similar to the case individuals but do not have the outcome of interest. The case-control study starts with a group of cases, which are the individuals who have the outcome of interest. A case-control study is a type of observational study commonly used to look at factors associated with diseases or outcomes.

Case control study