IQ and personality data were available for 646 twins. There were an additional 1307 twins with NEO-FFI data, and 535 with IQ data. Multivariate genetic structural equation modeling was carried out.
Significant positive phenotypic correlations with IQ were seen for agreeableness (r = 0.21) and openness to experience (r = 0.32). A negative correlation emerged for neuroticism and IQ (r = ?.10). Genetic factors explained (nearly) all of the covariance between personality traits and IQ. Genetic correlations were 0.3-0.4 between IQ and agreeableness and openness. The genetic correlation between IQ and neuroticism was around ?.18. Thus, personality and IQ did not appear to be independent dimensions, and low neuroticism, high agreeableness and high scores on openness all contributed to higher IQ scores.