To assess the proportion of phenotypic variance in the iPSYCH data explained by common variants we applied LD score regression and the GREML method implemented in GCTA, assuming a population prevalence of 1% for cannabis use disorder (Methods). Estimates of the liability-scale SNP heritability were h2snp=0.09 (SE=0.03) and h2snp=0.042 (SE=0.014; P=0.0012) using LD score regression and GCTA, respectively. This result suggest a smaller contribution from common variants than was previously found for cannabis use12. The estimate will probably increase with larger sample size as a result of a decrease in the size of the error terms of the SNP effect estimates21.
