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.