In our linear mixed model, we estimate the variance in case-control status explained by SNPs18 (heritability on the observed scale; CC estimates in Table 1). Cases in case-control samples are highly ascertained compared to in the population, and, because the cohorts for different disorders had different proportions of cases, CC estimates were difficult to interpret and compare. For this reason, we report hSNP2 values on the liability scale, in which a linear transformation18 is applied based on a user-specified estimate of the risk of the disorder in the study base population (disorder risk, K). For each disorder, we considered three values of K (Table 1), and we converted hSNP2 values to predicted risk to first-degree relatives (λ1st SNP) given K. We benchmarked the λ1st SNP risk values to risk to first-degree relatives (λ1st), consistent with estimates of heritability reported from family studies given K. Our estimates of λ1st SNP values were robust, and our estimates of hSNP2 values were reasonably robust, to the likely range of K values and show that a key part of the heritabilities or familial risk
