Conclusion
In externally controlled studies, the methods of g-computation, PS-based weighting (IPTW, OW and SMR), and TMLE can be used to minimize the biases due to measured and unmeasured confounders. However, the extent of bias reduction by these methods depends on the technique used and the existence of an unblockable confounding path for an unmeasured confounder. Our findings in this simulation study suggest that g-computation and OW are the preferable alternative approaches producing relatively unbiased estimates, especially when there is no large, unblocked confounding path for an unmeasured confounder.