Multivariate logistic regression for familial aggregation of two disorders. I. Development of models and methods

The question of whether two disorders cluster together, or coaggregate, wit hin families often arises. This paper considers how to analyze familial agg regation of two disorders and presents two multivariate logistic regression methods that model both disorder outcomes simultaneously. The first, a pro band predictive model, predicts a relative's outcomes (the presence or abse nce of each of the two disorders) by using the proband's disorder status. T he second, a family predictive model derived from the quadratic exponential model, predicts a family member's outcomes by using all of the remaining f amily members' disorder statuses. The models are more realistic, flexible, and powerful than univariate models. Methods for estimation and testing acc ount for the correlation of outcomes among family members and can be implem ented by using commercial software.