Depression defined by minimal phenotyping had lower SNP-based heritabilities (h2SNP) than more strictly defined versions (Fig. 3a). Self-report(SelfRepDeph2SNP = 11%, standard error (s.e.) = 0.85%) and help-seeking (Psypsy h2SNP = 13%, s.e. = 1.18%; GPpsy h2SNP = 14%, s.e. = 0.81%) definitions had heritabilities of 15% or less. By contrast, strictly defined MDD (LifetimeMDD) had a much higher h2SNP of 26% (s.e. = 2.15%); imposing the further criterion of recurrence brought the h2SNP up to 32% (s.e. = 2.56%). Other definitions had intermediate h2SNP. All h2SNP values were estimated on the liability scale using phenotype correlation-genotype correlation (PCGC)33 (Supplementary Note), and the trend held regardless of the method used33-36 (Supplementary Note and Supplementary Table 13). We further verified that the trend could not be explained by potential case prevalence misestimations (Fig. 3b, Supplementary Note, Supplementary Fig. 3 and Supplementary Table 13) and was not affected by regions of high linkage disequilibrium (LD) or complexity37 (Supplementary Note and Supplementary Fig. 3). We compared h2SNP estimates from previous studies of MDD4,38,39 (Supplementary Fig. 6) with our results and found that they fit squarely into the trend we observed: the less strict the criteria used to diagnose MDD, the lower the h2SNP.
