In summary, this work has demonstrated how subsample and 2-sample IV methods can be used to substantially enhance cost-efficiency for MR studies. For large studies with available genetic and outcome data, it will not be essential to obtain exposure data for all participants. Generating exposure data for a subset of participants will typically have a very limited impact on power, with the optimal size of this subset being determined by the strength of the IV. Furthermore, these methods potentially allow for the inclusion of participants for whom it is not feasible to collect biomarker data. These findings should increase the feasibility of MR for epidemiologists, especially those interested in utilizing existing genetic data or DNA samples from large-scale genetic association studies.
