Statistical methodology for estimating twin similarity with respect to a dichotomous trait

Statistical methodology is presented for the estimation of twin similarity with respect to a dichotomous trait. The methodology focuses on the intraclass correlation as the parameter of interest and is analogous to methodology commonly applied to continuous outcome data. For inference problems involving a single sample, confidence interval construction and significance testing are discussed. For two sample problems, test procedures are provided that are an alternative to an approach recently presented by Ramakrishnan et al. [(1992) Genet Epidemiol 9:273-287 (1)]. Two examples based on published data sets are given to illustrate the proposed techniques.