Prediction error of genetic relationship. The genetic relationship at unobserved causal loci is predicted, with error, from the relationship estimated from genotyped SNPs. The prediction error is calibrated by comparing the relationship at causal loci (mimicked by a set of random SNPs with MAF ≤ θ) to that estimated from another set of random SNPs. Values plotted on y-axis are (1−β) var(Ajk) (see Online Methods for the notations) calculated from different numbers of random SNPs (N) in both adult and adolescent datasets. The slope of each line is equal to 1.0, with R2 = 1.0. The intercept (c) is constant for a certain MAF threshold θ, and c = 6.2 × 10−6 (p-value = 2 × 10−14), 3.4 × 10−6 (p-value = 9 × 10−12), 1.8 × 10−6 (p-value = 4 × 10−10), 7.8 × 10−7 (p-value = 2 × 10−7) and 9.2 × 10−9 (p-value = 0.87, not significant) for θ = 0.1, 0.2, 0.3, 0.4 and 0.5, respectively.