Impact of nonrandom selection mechanisms on the causal effect estimation for two-sample Mendelian randomization methods.
Nonrandom selection in one-sample Mendelian Randomization (MR) results in biased estimates and inflated type I error rates only when the selection effects are sufficiently large.In two-sample MR, the different selection mechanisms in two samples may more seriously affect the causal effect estimation.Firstly, we propose sufficient conditions for cau