R语言做了两样本孟德尔随机化(MR)，用network（two-step）MR做中介分析，Proportion mediated = Indirect effect / Total effect= (a*b) / c
the MR analysisfrom exposure to mediator getting an estimate of a; the MR analysis frommediator to outcome getting an estimate of b, and the MR analysisfrom exposure to outcome getting an estimate of c.

怎么用delta法求Proportion mediated的置信区间呢