Published online by Cambridge University Press: 01 August 2014
A twin population model is proposed, and two different definitions of the rate of concordance are investigated within the context of this model. It is found that the statistic formed from the ratio of the number of affected twins that come from concordant pairs to all affected twins has certain advantages over the traditional definition of the rate of concordance. This twin population model is extended to nontruncated sample of twins. The parameters of this situation are estimated. Finally, it is shown how these parameters relate to the two usual estimates of the proportion of DZ. twins in a twin population, and the efficiency of these methods is computed.