# #StackBounty: #propensity-scores #treatment-effect #weights Stabilized propensity weights: intuition and ATT formula

### Bounty: 50

The average treatment effect (ATE) of binary treatment T on outcome Y can be estimated using inverse propensity weights:

$$begin{equation}nonumber frac{sum_{i=1}^{N}t_ihat{pi}i^{-1}y_i}{sum{i=1}^{N}t_ihat{pi}i^{-1}}-frac{sum{i=1}^{N}(1-t_i)(1-hat{pi}i)^{-1}y_i}{sum{i=1}^{N}(1-t_i)(1-hat{pi}_i)^{-1}} xrightarrow{p} E[Y^1]-E[Y^0] end{equation}$$

where $$hat{pi}_i$$ is the estimated propensity for individual $$i$$.

To avoid extreme weights, there is a literature that suggests replacing the numerator of the treated weights with the marginal probability of treatment, $$p(t=1)$$, and the numerator of the control weights with $$1-p(t=1)$$. I see how this makes the weights milder, but why those particular numerators? What is the intution of this stabilization?

Also, the average treatment effect on the treated (ATT) can be estimated by weighting control units with the odds:

$$begin{equation}nonumber frac{sum_{i=1}^{N}t_iy_i}{sum_{i=1}^{N}t_i}-frac{sum_{i=1}^{N}(1-t_i)hat{pi}i(1-hat{pi}_i)^{-1}y_i}{sum{i=1}^{N}(1-t_i)hat{pi}_i(1-hat{pi}_i)^{-1}} xrightarrow{p} E[Y^1|T=1]-E[Y^0|T=1] end{equation}$$

How should one stabilize these $$hat{pi}_i(1-hat{pi}_i)^{-1}$$ weights?

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