Path analysis of seven fear factors in adult twin and sibling pairs and their parents.

A multivariate path model of genetic and environmental transmission, used to derive expected covariances among adult twin and sibling pairs and their parents, was fitted to fear factor data from 250 twin families and 91 sibling families, with the use of a maximum-likelihood estimation procedure. The full model, with 259 free parameters, provides for parental cultural transmission, common twin and sibling environment, genotype-environment correlation, direct assortative mating, and genetic and environmental correlations. Significant effects were indicated for heritable transmission of common fears and phobias, and a single genetic factor accounted for most of the genetic covariance among the traits. Moderately high levels of common twin environment and a small effect for direct isomorphic marital assortment were also found. There was no evidence for cultural transmission, genotype-environment correlation, or common sibling environment.