To more definitively assess the true extent of transcriptomic heritability for our study, we modeled true h2 as following a gamma distribution, with sampling variation determined by the ACE model. The result (Figure 3a) is a shrunken distribution with a similar mean h2 but markedly less variation. The model estimates that the true proportion of expressed genes with heritability > 0.3 is actually only 7.9%. For high heritability thresholds, the differing results across studies can appear to be dramatic – while the MuTHER report estimated >700 expressed genes in both skin and LCLs with heritability >0.5, we estimate the true number in our study as ~100. The studies differ in tissue and platform (the MuTHER study used the Illumina HT-12 BeadChip platform), NTR mean age was ~20 years younger, and the NTR samples included both sexes. Removal of age as a covariate (Supplementary Note) suggests that it was not an important heritability determinant in NTR. However, the important effect of sampling variation has not been fully explored. First, we assessed the gamma fit by artificially adding sampling error to the
