To further corroborate evidence of polygenic variation, we tested whether phenotypes for intelligence could be predicted solely from SNP data32,33. We performed cross-validation analyses in which four of the five CAGES cohorts were used to estimate SNP effects while the remaining cohort was used to estimate the correlation between the phenotype and the predictor created from all autosomal SNPs (Table 2 and see Supplementary Method for further detail). For gf, four of the five prediction analyses showed significant (P < 0.05) results. The correlations for the five analyses fell consistently in a narrow band of values between 0.067 and 0.148 (mean R = 0.11). For gc, three of the five prediction analyses showed significant results, and the correlations for the five analyses ranged between 0.049 and 0.133 (mean R = 0.081). Non-significance of some of the associations in Table 2 should not be taken to mean that there are different results in different cohorts. The standard errors of the estimates of correlation in Table 2 vary from ~0.03 (LBC1936) to ~0.05 (LBC1921), and none is significantly different from the other, either by trait or by validation cohort.
