Methodological issues in case-control studies: II. Test statistics as measures of efficiency.

The ratio of test statistics has been used to compare the efficiency of matched and unmatched designs, and stratified and pooled analyses for case-control studies. The index has been computed for a wide range of population conditions and it is concluded that (a) pooled analysis is always more efficient than stratified analysis when such pooling leads to a valid estimate of the relative risk, (b) the loss of efficiency by matching in the classic overmatching situation can be substantial, (c) in the confounding situation either design may be more efficient but generally the difference is small. These results add support to the contention that matching is rarely justified in case-control studies.