Ignoring relatedness and assuming complete independence between participants, among the full sample of ever-drinking participants there was >80% power to detect additive per-allele individual SNP effects as small as a .09 difference in alcohol abuse and dependence symptom count, or a .13 difference in the drinking index, corresponding to a difference in R^2 = .004 for either phenotype. Assuming full dependence between first degree relatives, and therefore basing calculations only on founders who had ever had a drink, there was >80% power to detect individual SNP effects of .11 alcohol abuse and dependence symptoms per allele, and a .16 difference in the drinking index per allele, corresponding to a difference in R^2 = .006. The mean cross-validated squared correlations between polygenic score-predicted phenotypic values and observed phenotypic values at each of 10 p-value thresholds are shown in Table 4. The mean was computed as a weighted average of the 10 squared correlations with weight given as the sign of the unsquared correlation. A few of the resulting means were slightly negative but truncated to 0 because a squared correlation cannot
