Heredity, Environment, and the Structure of the California Psychological Inventory

Scores were obtained on 31 item-clusters from the California Psychological Inventory (CPI) for 490 identical and 317 same-sex fraternal twin pairs from the National Merit twin sample. Ordinary and cross-pair correlations were calculated and used to derive three matrices hypothesized to reflect the influence of the genes (G), shared environment (S), and unshared environment (U). Each of these matrices was factor analyzed. The factors from the G and U matrices were similar, and typical of those usually found in factor analyses of personality inventories, including major extraversion-introversion and emotional maladjustment dimensions. The S factors were different, featuring a possibly artifactual gender factor and a family problems factor. These results were partially supported in confirmatory analyses based on another twin sample and a sample of adoptive siblings.