A complementary approach is to estimate genetic correlation, which includes the effects of all SNPs, including those that do not reach genome-wide significance (Methods). The two main existing techniques for estimating genetic correlation from GWAS data are restricted maximum likelihood (REML) [11, 12, 13, 14, 15, 16] and polygenic scores [17, 18]. These methods have only been applied to a few traits, because they require individual genotype data, which are difficult to obtain due to informed consent limitations.
