Technical Considerations. Second, effect sizes are (mostly) modest with PRS explaining <1% of the variance for correlated traits [e.g., R2 for negative symptoms in the population is 0.007, or 0.7%; (Jones et al., 2016) or 0.3% for cognitive abilities (Riglin et al., 2017). These effect size estimates are sobering; even for highly correlated disorders, such as SCZ and Bipolar Disorder (Charney et al., 2017), PRS rarely account for more than 3% of variance in a trait [e.g., 2.5% for educational attainment PRS predicting cognitive function (Rietveld et al., 2013)]. Thus, studies accounting for >5% of variance in cross-trait prediction, or with fewer than several-hundred participants, should be viewed with some skepticism when using current GWAS summary statistics.
