Matching is the process of selecting a comparison group so that it is equivalent in terms of certain characteristics (e.g., age or gender) to the group to which it will be compared. Matching is most often used for selection of controls in case-control studies; however, it may be applied in cohort studies as well. This entry describes benefits and drawbacks of matching, as well as the analysis methods applied to matched data. Unless otherwise stated, the discussion refers to matching in case-control studies.

Matching can be performed in different ways. In individual matching, one or several controls are selected for each case so that they are equivalent to the case for their values of the variables being matched on. For example, if a case was a ...