The use and misuse of matching in case-control studies: the example of polycystic ovary syndrome.

Matching control selection strategies are often used in polycystic ovary syndrome case-control studies; however, they are infrequently used in an appropriate fashion. When properly applied, matching may offer improved study precision, but this is highly contingent on the causal pathway under consideration, strength of the associations between the matching variable and both the risk factor of interest and polycystic ovary syndrome, and the use of an appropriate stratified data analysis.