phenotypic variance in cigarette consumption,17 whereas the polygenic risk score for height captures approximately 9% of phenotypic variance.18 We controlled the baseline risk of selection into the sample, resulting in a selected sample of approximately 500 000 people. The analysis was an unadjusted regression of outcome on allele score (i.e. not adjusting for the phenotype). We simulated a true null association (i.e. in the intended study population, the regression coefficient for outcome on allele score is zero). We simulated each scenario 100 times. We then repeated the simulations with the addition of a causal effect of the phenotype on the outcome, with a regression coefficient of 0.1.
