Fig 4. The effect of correlation r_g between the direct and indirect effect sizes on PGS regression coefficients from different study designs.

y-axis shows the ratio of the PGS regression coefficients from between family design (red) or sibling difference design (blue) vs. 1, which is the effect size of the PGS_dir (see Table 1). We used the same simulation settings as those used in Fig 3. Since we set the variance of the direct effect size ${\sigma }_{dir}^2=1$, when the variance of the indirect effect size is also 1 and their correlation is -1, the direct and indirect effect sizes become exactly the opposite of each other, therefore PGS_mix = 0 and the linear regression cannot be run under this scenario. Therefore, we do not include results when ${\sigma }_{ind}^2=1$ and ρ_g = −1.