Multivariate Familial Analysis of Cognitive Measures in the Colorado Family Reading Study.

Multivariate path analysis is employed to examine the etiologies of variation and covariation of three composite cognitive measures in the Colorado Family Reading Study: reading ability, symbol-processing speed, and spatial/reasoning. Measures of phenotypic assortative and cross-assortative mating are incorporated in a multivariate analysis of familial resemblance within nuclear families. Phenotypic variances and covariances are partitioned into components due to familial (genetic and/or family environmental) influences and to specific, nontransmissible environmental influences in families with a reading-disabled child as well as families with children of normal reading ability. Comparable moderate familial influences are found across family type for all three composites and the phenotypic correlations between traits are largely due to familial influences.