We are interested in estimating the average effect of a binary treatment on a scalar outcome. If assignment to the treatment is exogenous or unconfounded, that is, independent of the potential outcomes given covariates, biases associated with simple treatment-control average comparisons can be...

With panel data important issues can be resolved that can not be addressed with cross--sectional data. A major drawback is that panel data suffer from more severe missing data problems. Adding a sample consisting of new units randomly drawn from the original population as replacements for units...

This paper develops a new efficient estimator for the average treatment effect, if selection for treatment is on observables. The new estimator is linear in the first-stage nonparametric estimator. This simplifies the derivation of the means squared error (MSE) of the estimator as a function of...