Reader reaction: Confounding in epidemiologic studies.

In twin studies (and other matched-pair studies) of the effect of a K-level risk factor on disease risk, one must estimate the proportion of pairs in each of K2 possible pair categories, of which K(K -1) categories represent discordant pairs. In particular, for a binary factor, one must estimate proportions within two discordant-pair categories and the variances of functions of these estimates. This paper shows how to do so when misclassification is present and stable estimates of the classification rates are available. Unlike methods that estimate only the discordance ratio, one can use the methods presented here to improve estimates of epidemiologic effects. (Author/publisher)