11. Phillips, K. (1989). Delta path methods for modeling the effects of multiple selective associations in adoption designs. Behavior Genetics, 19, 609-620.

In analyses of family data, multiple direct association processes can be modeled by use of delta path methods, especially the transitivity principle. The method is described for the case of an adoption study involving potential selective matching of adoptive parents to two sets of biological parents of adopted offspring in the presence of assortative mating for both wed and unwed couples. Second and third order delta paths may be derived by application of the transitivity principle, and these higher order paths are very convenient in formulating expectations that are due to direct and indirect association processes. Expectations are derived for re-semblance among all adults in this three-couple adoption system; examples are given also for deriving parent-offspring expectations to illustrate the general use of higher order delta paths in structural models of familial resemblance. Matrix notation is employed in order to facilitate the application of the methods indevelopmental and/or multivariate models.