Familial analysis of qualitative traits under multifactorial inheritance

The analysis of family data is described for qualitative multifactorial traits. For such a trait, affectational status is determined by an underlying liability distribution with one or more thresholds. The distribution of families (either selected at random or through probands) is used to estimate sex‐specific parent‐offspring and sibling correlations in liability and the prevalence in each sex. In contrast to using pairs of relatives, this approach permits estimation of age‐specific population prevalences without a control sample. Moreover, by allowing for sex‐specific correlations and a correlation between mates, path analysis can be used to model and test various cultural transmission models in addition to polygenic inheritance. Parameter estimation, hypothesis testing, and a goodness‐of‐fit test for path analytic models are described, and a computer program implementing these procedures is outlined.