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…

Procedures for analyzing common item effects on interscale structure were reviewed and a study using smallest space analysis of the California Psychological Inventory (CPI) reported. Solutions of three matrices--intercorrelation matrix of the original CPI scales, of reduced scales (with common items removed), and of the number of common…