Components of variation in normal personality.

Applied a random effects linear model to personality data (e.g., the Eysenck Personality Questionnaire and the Comrey Personality Scales) gathered from 138 adult Swedish twins and their families. The multiple relationships surrounding the twins allowed for the estimation of variance fractions due to several genetic and environmental factors. A striking pattern of similarity among personality traits emerged. All variables were characterized by having near-zero additive genetic, small–moderate nonadditive genetic, negligible prenatal, small postnatal familial, and quite large postnatal extrafamilial effects. Personality traits were influenced primarily by the environment, especially those outside the home. Genetic influences were confounded by cultural factors. It is suggested that temporal instability, genetic epistasis, or both could be underlying factors that unify the results for personality variables. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)