Fig. 2.

Quantile-quantile plots of p-values from different global mediation tests in the simulation study for the continuous outcome. The observed p-values were compared to the expected quantiles generated by the uniform null distribution. The $|{\mathcal{S}}_{\alpha }|$ and $|{\mathcal{S}}_{\beta }|$ denote the number of treatment-associated OTUs and outcome-associated OTUs, respectively. Different combinations of ($|{\mathcal{S}}_{\alpha }|$, $|{\mathcal{S}}_{\beta }|$) represent different mixtures of mediation nulls $H_{00}$, $H_{10}$, and $H_{01}$