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We examined whether attained socioeconomic status (SES) moderated genetic and environmental sources of individual differences in cognitive performance using pooled data from 9 adult twin studies. Prior work concerning SES moderation of cognitive performance has focused on rearing SES. The current adult sample of 12,196 individuals (aged 27-98 years) allowed for the examination of common sources of individual differences between attained SES and cognitive performance (signaling potential gene-environment correlation mechanisms, rGE), as well as sources of individual differences unique to cognitive performance (signaling potential gene-environment interaction mechanisms, G × E). Attained SES moderated sources of individual differences in 4 cognitive domains, assessed via performance on 5 cognitive tests ranging 2,149 to 8,722 participants. Attained SES moderated common sources of influences for 3 domains and influences unique to cognition in all 4 domains. The net effect was that genetic influences on the common pathway tended to be relatively more important at the upper end of attained SES indicating possible active rGE, whereas, genetic influences for the unique pathway were proportionally stable or less important at the upper end of attained SES. As a noted exception, at the upper end of attained SES, genetic influences unique to perceptual speed were amplified and genetic influences on the common pathway were dampened. Accounting for rearing SES did not alter attained SES moderation effects on cognitive performance, suggesting mechanisms germane to adulthood. Our findings suggest the importance of gene--environment mechanisms through which attained SES moderates sources of individual differences in cognitive performance.

Numerous studies have found interactions between socioeconomic status (SES) and the heritability of cognitive ability in samples from the United States, with individuals from lower SES backgrounds showing decreased heritability compared to those reared in higher SES environments. However, nearly all published studies of the Scarr-Rowe interaction have been univariate and cross-sectional. In this study, we sought to maximize statistical power by fitting multivariate models of gene (G) x SES interaction, including longitudinal models. Cognitive ability data collected at up to five time points between ages 7 and 15 years were available for 566 twin pairs from the Louisville Twin Study. We used multilevel and latent factor models to pool intelligence subtest scores cross-sectionally. To examine interactions longitudinally, we fit latent growth curve models to IQ scores. Power analysis results indicated that the multivariate approach substantially boosted power to detect G x SES interaction. The predicted interaction effect was observed at most ages in cross-sectional multivariate analyses. In longitudinal analyses, we found significant G x SES interactions on mean-level (intercept) full scale IQ and performance IQ (p s <.001), but not verbal IQ intercept (p =.08). SES did not significantly moderate the heritability of change in IQ over time (slope). Interaction appeared to be driven by DZ twin correlations decreasing more substantially as a function of higher SES than MZ correlations. • G x SES interaction on intelligence is found across mid-childhood/early adolescence. • The interaction appears to be driven by divergence in DZ twins. • Multivariate methods boost power to detect G x SES interaction. [ABSTRACT FROM AUTHOR]