Evidence for the Scarr-Rowe effect on genetic expressivity in a large US sample.

Using the Continuous Parameter Estimation Method (CPEM), a large genotyped sample of the population of Wisconsin, USA (the Wisconsin Longitudinal Study, N=8,509) is examined for evidence of the Scarr-Rowe effect, an adverse gene x environment (GxE) interaction that reduces the heritability of IQ among those with low socioeconomic status. This method allows the differential expressivity of polygenic scores predictive of both educational attainment and IQ (EA3) on the phenotype of IQ to be operationalized throughout the full range of these variables. Utilizing a parental SES factor-weighted composite as a measure of childhood SES, evidence for the Scarr-Rowe effect was found, i.e. the genetic expressivity of EA3 on IQ increased with increasing parental SES ({beta}=.064, p=3.82x10-9, df=8508). The effect was found for both the male and female samples separately ({beta}(males)=.051, p=.002, df=4062; {beta}(females)=.076, p=1.76x10-7, df=4445) -- there were no significant sex differences in the effect magnitudes, however. The effects were furthermore robust to removing outlying values of parental SES.