A self-reporting personality inventory with 20 scales, meant to represent vernacular and recognizable traits. Unlike the Five-factor model, these traits aren’t meant to be orthogonal; some correlate highly with others.
Bouchard, T. J., Mcgue, M., Hur, Y.-M., & Horn, J. M. (1998). A genetic and environmental analysis of the California Psychological Inventory using adult twins reared apart and together. 14.