Socioeconomic status and heritability of cognitive performance in the Louisville Twin Study

Turkheimer et al. (2003) found that heritability of IQ varies as a function of socioeconomic status (SES) in 7 year-old children, with children from impoverished families showing reduced heritability compared to affluent... [ view full abstract ]

Turkheimer et al. (2003) found that heritability of IQ varies as a function of socioeconomic status (SES) in 7 year-old children, with children from impoverished families showing reduced heritability compared to affluent peers. The current study extended this line of work by examining interactions of SES and IQ heritability in children of other ages, using data from the recently resurrected Louisville Twin Study (LTS). It also built upon preliminary, previously reported analyses of the updated LTS (Turkheimer et al., 2015).

Comprehensive Wechsler IQ data (including Full Scale IQ, Verbal IQ, Performance IQ, and all subtest scores) were available for twins aged 7 to 15 years. Sample sizes ranged from 374 to 505 twin pairs (ages 15 and 8, respectively). We modeled the interaction of additive genetic (A) and shared environmental (C) variance in IQ with SES, which was also included as a linear and quadratic main effect (i.e., SES and SES2). We used a revised Purcell model of the interaction, which allows for phenotypic changes in variance that are independent of changes in the standardized twin correlations. The expected patterns of association (i.e., decreased heritability of IQ at low levels of SES and increased heritability at high levels) were observed for most analyses. However, the strength and significance of poverty x IQ heritability interaction fluctuated across ages and index scores/subtests in univariate analyses, likely due to a lack of power. Results of multivariate analyses (hierarchical and latent factor models) were more consistently significant. 

Turkheimer, E., Haley, A., Waldron, M., D’Onofrio, B., & Gottesman, I.I. (2003). Socioeconomic status modifies heritability of IQ in young children. Psychological Science, 14, 623–628.

Turkheimer, E., Beam, C.R., Finkel, D., Davis, D.W., & Dickens, W.T. (2015). Investigating poverty by heritability interactions in the Louisville Twin Study. Paper presented at the Behavior Genetics Association annual meeting, San Diego, CA.