Explicit Form of the Asymptotic Variance Estimator for IPW-type Estimators of Certain Estimands

Confidence intervals (CI) for the IPW estimators of the ATT and ATO might not always yield conservative CIs when using the 'robust sandwich variance' estimator. In this manuscript, we identify scenarios where this variance estimator can be employed to derive conservative CIs. Specifically, for the ATT, a conservative CI can be derived when there's a homogeneous treatment effect or the interaction effect surpasses the effect from the covariates alone. For the ATO, conservative CIs can be derived under certain conditions, such as when there are homogeneous treatment effects, when there exists significant treatment-confounder interactions, or when there's a large number of members in the control groups.