Correlations on subscales of Wechsler intelligence quotient tests and the Revised Beta Examination were obtained for biologically related and unrelated individuals in 181 adoptive families in the Texas Adoption Project. Generally higher correlations for biologically related individuals support the importance of genetic influence in intellectual…

Scores were obtained on 31 item-clusters from the California Psychological Inventory 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 genes, shared environment, and unshared…

Raymond Cattell's efforts to sort out the relationships of genetic or environmental patterns to personality factors have contributed to behavior genetics. Early writings on the projected decline of intelligence in Britain, studies using Multivariate Abstract Variance Analysis, and other miscellaneous studies on personality factors and mental…