Term: Case Control Study

Description:

A case-control study is an analytical study which compares individuals who have a specific disease ("cases") with a group of individuals without the disease ("controls"). The proportion of each group having a history of a particular exposure or characteristic of interest is then compared. An association between the hypothesized exposure and the disease being studied will be reflected in a greater proportion of the cases being exposed. It is advantageous for the controls to come from the same population from which the cases were derived, to reduce the chance that some other difference between the groups is accounting for the difference in the exposure that is under investigation. A case-control study generally depends on the collection of retrospective data, thus introducing the possibility of recall bias. Recall bias is the tendency of subjects to report events in a manner that is different between the two groups studied. People who have a disease may be more likely to remember exposures more readily than those without the disease. The opportunities to effectively use case-control studies may expand as new ways of characterizing exposure through the use of biological markers of exposure are developed, which would reduce the problem of recall bias.

Applications:
Why use them? Who uses them? We use Case Control Studies because they are a relatively inexpensive and frequently-used type of epidemiological study that can be carried out by small teams or individual researchers in single facilities in a way that more structured experimental studies often cannot be. They have pointed the way to a number of important discoveries and advances, but their retrospective, non-randomized nature limits the conclusions that can be drawn from them.

Usefulness and Drawbacks
Case-control studies are a relatively inexpensive and frequently used type of epidemiological study that can be carried out by small teams or individual researchers in single facilities in a way that more structured experimental studies often cannot be. Compared to prospective cohort studies they tend to be less costly and shorter in duration. The case-control study design is often used in the study of rare diseases or as a preliminary study where little is known about the association between the risk factor and disease of interest. One of the most effective examples of a case control study was the demonstration of the link between tobacco smoking and lung cancer, by Richard Doll and Bradford Hill. They showed a statistically significant association in a large case-control study. However there are some drawbacks to case control studies. One of the major drawbacks is that case control studies is that they do not provide the same level of evidence as randomized controlled trials. The results may be confounded by other factors, to the extent of giving the opposite answer to better studies.The most important drawback in case-control studies relates to the difficulty of obtaining reliable information about an individual’s exposure status over time. Case-control studies are therefore placed low in the hierarchy of evidence.







Web Resources:
http://www.ahc.umn.edu/
http://berkeley.edu/Health/Health.stm


Related Terminology:
Cases, Studies, Experiments, In Field experiments, hierarchy of evidence, randomized control trials