quantity H2 = (σd 2 + σg 2)/(σd 2 + σg 2 + σe 2) provides a liberal estimate of the overall impact of genes on the phenotype at hand, whereas in the model attributing any excess similarity between siblings to shared environment, the quantity h2 = σg 2/(σs 2 + σg 2 + σe 2) provides a very conservative estimate of the overall impact of genes. Whenever there was significant evidence (p < 0.001) for shared sibling environment or genetic dominance, genetic dominance was included in the heterogeneity analyses described below.
