To match or not to match? Methodological issues in autism-related research.

Studies of autism typically adopt a factorial matched-groups design aimed at eliminating nonspecific factors such as mental retardation as explanations of performance on experimental tasks. This paper reviews the issues involved in designing such studies and interpreting their results and suggests that the best approach to matching may be to equate performance on carefully designed control tasks. However, we also argue that the interpretation of such studies is often complicated by the fact that associations between background measures and experimental task performance are not clear. Consequently, we also advocate the use of regression techniques that allow the researcher to determine the factors that relate to task performance and to assess the extent of group differences on the task of interest having taken these factors into account.