Guide to Research Methods - Case Control Studies

Case Control Studies

Case control studies are studies in which patients who already have a certain condition are compared with people who do not.

For example: a study on which lung cancer patients are asked how much they smoked in the past and the answers are compared with a sample of the general population would be a case control study.

Case control studies are less reliable than either randomized controlled trials or cohort studies. Just because there is a statistical relationship between two conditions does not mean that one condition actually caused the other. For instance, lung cancer rates are higher for people without a college education (who tend to smoke more), but that does not mean that someone can reduce his or her cancer risk just by getting a college education.

The main advantages of case control studies are:

They can be done quickly. By asking patients about their past history, researchers can quickly discover effects that otherwise would take many years to show themselves.
Researchers don't need special methods, control groups, etc. They just take the people who show up at their institution with a particular condition and ask them a few questions.

The first study to suggest a new medical conclusion will often be a case control study, perhaps designed to check on a hypothesis suggested by a case series. If possible, researchers will generally try to confirm the results with a randomized controlled trial or a cohort study.