Pair-matching-a reappraisal of a popular technique.

Pair-matching is undoubtedly one of the most popular techniques for controlling variation in both medical and other investigations involving human populations. Given the obvious advantages of ease of implementation and comprehension, apparent efficiency and simplicity of analysis, this popularity is understandable. Despite this appeal, however, pair-matching frequently involves high cost (particularly in the loss of unmatchable units), cannot claim efficiency when appropriate comparisons of precision are made, and suffers some important limitations in the analysis which directly affect inference. The persistence of the technique in the face of these limitations is discussed with reference to the disjunction between theoretical models and practical research constraints. It is concluded that this design may not be the optimal choice in many, if not most, research situations.