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 be negative. The cross-validated squared correlation was uniformly small (in no case even approaching 1%) and not significant at any threshold for either phenotype. Ignoring relatedness and assuming independence between participants, we had 68% power to detect the largest observed R^2 of approximately .001 (for alcohol abuse and dependence symptoms at the p<0.1 level, non-significant). Among ever-drinking founders only, we had 49% power to detect an R^2 = .001, for either phenotype. To obtain >80% power to detect a polygenic effect of R^2 = .001 or smaller would require a sample size of at least N = 8173 independent (non-related) participants.
