I am using the doubly robust estimator IPTW-RA to estimate the average treatment effect parameters (ATE, ATET and ATU). However, after computing the first two (i.e., ATE and ATET), I do not seem to find my way on how to compute the average treatment effect for the untreated (i.e., ATU). I will highly appreciate if someone help me out on how I can compute the ATU using the IPTW-RA estimator.

Thank you in advance