error (SE) of depends only on sample size, and is approximately . We show by simulations based on real genotype data (Text S1) that this approximation is very accurate (Figure 1 and Table S1). The SEs calculated from the approximation theory are also highly consistent with those reported from our previous studies for human height and body mass index (BMI). For example, the reported SE of for height was 0.083 using 3925 unrelated samples [3] and 0.029 for both height and BMI, irrespective to , using 11586 unrelated samples [22], and the SE calculated from the approximation theory is 0.081 for N = 3925 and 0.027 for N = 11586.
