Use of conditional and marginal odds-ratios for analysing familial aggregation of binary data

We propose a method for measuring familial aggregation of binary outcomes that incorporates unconditional, i.e., marginal, odds-ratios, for measuring association between outcomes within generations while using conditional odds-ratios to measure association between generations. This method may be used together with marginal odds-ratio models to explore the strength of association between individuals within a generation while accounting for the outcomes of predecessors. Interpretation of resulting odds-ratios is straightforward and a number of features of the method are discussed. An example, using smoking status data from Busselton Health Study families, is used to illustrate our approach.