Self-rated personality and intelligence: a multivariate genetic analysis

Infant SES as a predictor of personality--is the association mediated by intelligence?

Background

Although research into the continuity and change of personality traits during a lifespan has been fairly extensive, little research has been conducted on childhood predictors of adult personality.

Purpose

We aimed to investigate the association between infant socioeconomic status (SES), and Eysenck personality traits in adulthood. An additional aim was to investigate whether intelligence and education may mediate this association.

Methods

SES of 9125 children in the Copenhagen Perinatal Cohort was recorded at a 1-year examination. A subsample of this cohort, comprising 1182 individuals, participated in a follow-up at 20–34 years and was administered the Eysenck Personality Questionnaire (EPQ) which includes measures of neuroticism, extraversion, psychoticism and the so-called lie-scale. Associations of SES with each of the four personality traits were analysed by bivariate and partial correlations, and the mediating effects of intelligence and years of education were analysed.

Results

Higher SES in infancy was associated with lower neuroticism (r = −0.06; p = 0.05), lower lie-scale scores (r = −0.11; p = 0.0002), and higher psychoticism (r = 0.09; p = 0.003). However, analyses of mediation revealed no direct effect of infant SES on any of the adult personality traits, but only indirect effects mediated by intelligence and years of education, with intelligence being the main mediating factor.

Conclusion

Only weak associations were observed between infant SES and personality in young adulthood, and the observed associations were mediated by adult intelligence and educational level. Thus, factors associated with infant SES or family background appears to have weak direct effects on personality development.

The Jackson Career Explorer

The present report consists of two further validity studies using the Jackson Career Explorer (JCE), a short form and continuous version of the Jackson Vocational Interest Survey, measuring 34 interests. The first study examined the relationships between the JCE and five personality factors, from a sample of 528 individuals. The correlations found typically replicate the pattern of relationships found between vocational interests and personality. The second study examined the JCE in relation to Holland’s Vocational Preference Inventory in a sample of 270 individuals. Convergent correlations were found between the two interest measures. The results further support the use of the JCE as a measure of vocational interests.

Heritability of NEO PI-R Extraversion Facets and Their Relationship With IQ

In recent years, there has been a renewed interest in the relationship between intelligence and personality. Extraversion, in particular, has been suggested to influence intelligence, but the direction of this relationship has been controversial (Wolf & Ackerman, 2005). In a young adult sample, the NEO PI-R was completed by 103 pairs of monozygotic twins, 181 pairs of dizygotic twins and 210 of their nontwin siblings. IQ data (Multidimensional Aptitude Battery) were available for approximately three quarters of this sample, and were collected at 16 years as part of an ongoing study of cognition conducted by the Queensland Institute of Medical Research. All extraversion facets were significantly influenced by genes with both additive and nonadditive genetic effects being important (heritabilities ranged from .25 for activity to .54 for warmth). While a significant correlation between the extraversion domain score and IQ was not found, the extraversion facet of excitement-seeking (E5) was significantly negatively correlated with both verbal (r= −.15) and performance (r= −.11) IQ scores. The facet of gregariousness was significantly correlated with verbal IQ only (r= −.09). The relationship between excitement-seeking and IQ was further shown to be solely due to additive genetic influences. These common genetic effects may stem from a dependence on brain dopamine, a neurotransmitter that has been implicated in both personality and cognition.

The Relationship Between Personality and Self-Report Abilities

The relationship between self-report abilities and personality was examined at both the phenotypic (zero-order) level as well as at the genetic and environmental levels. Twins and siblings (N = 516) completed self-report ability and personality questionnaires. A factor analysis of the ability questions revealed 10 factors, including politics, interpersonal relationships, practical tasks, intellectual pursuits, academic skills, entrepreneur/business, domestic skills, vocal abilities, and creativity. Five personality factors were examined, including extraversion, conscientiousness, dependence, aggression, and openness. At the phenotypic level, the correlations between the ability factor scores and personality factor scores ranged from 0 to .60 (between political abilities and extraversion). The relationship between the two areas at the genetic level was found to range between –.01 and .60; the environmental correlations ranged from –.01 to .48. The results suggest that some of the self-report ability scores are related to self-report personality, and that some of these observed relationships may have a common genetic basis while others are from a common environmental factor.