An exploration of genetic g: Hierarchical factor analysis of cognitive data from the western reserve twin project

Hierarchical factor analyses involving Schmid-Leiman transformations (Schmid & Leiman, 1957) were conducted on specific cognitive abilities data collected in a sample of 148 identical (MZ) and 135 same-sex fraternal (DZ) twin pairs. Two main questions were addressed: First, are genetic influences on specific cognitive abilities simply a reflection of their g loading, or are different sets of genes affecting separate abilities? Second, to the extent that specific cognitive abilities are affected by common genetic variance, how similar is the common genetic factor to a phenotypic factor reflecting g? Model fitting results suggest that genetic influences on specific abilities are a reflection of both general intelligence and genetic influences specific to separate abilities and that loadings on the common genetic factor are more highly correlated with phenotypic g loadings than are common environmental factor loadings.