A researcher is interested in the impact of joining a weight loss program in the past 12 months on the individuals weight loss. The analysis was restricted to people aged 16 and older who answered yes...

A researcher is interested in the impact of joining a weight loss program in the past 12 months on the individuals weight loss. The analysis was restricted to people aged 16 and older who answered yes to the question "During the past 12 months, have you tried to lose weight?" About 5% of the sample had joined a weight loss program in the past year.

The researcher has decided to use propensity score analysis. What would be the appropriate estimator for this analysis:

Average treatment effect (ATE), Average treatment effect on the treated (ATT) or average treatment effect on the untreated (ATU)