We quantified the proportion of phenotypic variation accounted for by all genotyped SNPs, using an analysis method we recently developed28 (See Supplementary Method for further details and Supplementary Figure 8). This model is mathematically equivalent to fitting all SNPs in the model, provided that the SNP effects are treated as random28. Therefore, our estimate of additive genetic variance is that explained from considering all SNPs simultaneously. Because there are many more ungenotyped genetic variants in the genome than there are genotyped SNPs, this is likely to be due to LD between genotyped SNPs and unknown causal variants. Further details on and explanation of this method can be found in a recent detailed commentary on the method provided by Visscher and collegaues30. We estimated that a proportion of 0.40 (SE = 0.11, P = 5.7 × 10−5, likelihood-ratio test) and 0.51 (SE = 0.11, P = 1.2 × 10−7, likelihood-ratio test) of the phenotypic variance can be explained by all SNPs for gc and gf, respectively (Table 1). Analysing the English and Scottish samples separately or fitting 20 principal components as
