No Clear Link between G Loadings and Heritability: A Twin Study from Korea
A fundamental theoretical question in intelligence research is to what extent the g factor and heritability coefficients of the subtests of an IQ battery are correlated. Five studies from Western countries showed modest to strong positive correlations (range = 43-.77), and six studies from a Japanese meta-analysis showed zero to modest correlations (range = −0.01–0.59). The Western and Japanese studies were compared with a Korean sample of 24 monozygotic and 20 dizygotic young adult twin pairs administered the Korean Wechsler Adult Intelligence Scale-Revised (WAIS-R). A univariate twin model was applied to all subscale scores leading to estimates of heritability for all scales, g loadings were also computed using principal-axis factor analysis. Finally, the correlation between the heritabilities and the g loadings of these scales were computed. The correlations of r = −.15 were not in line with previous studies. It could be that Spearman's hypothesis is less strongly confirmed for Northeast Asians, but it is also possible that the study will be an outlier in a future meta-analysis. More primary research and a meta-analysis of all studies are needed.