This estimate can also be obtained from individual‐level data using the 2‐stage least squares method.16 Alternatively, the causal effect of the risk factor on the outcome can be estimated using a weighted linear regression of the genetic association estimates,17 with the intercept set to zero: (3)β^Yj=θUIβ^Xj+ϵUIj,weights=se(β^Yj)−2.
