The Local Average Treatment Effect (LATE) interpretation of the IV estimates of the returns to schooling is becoming increasingly popular. Typically, researchers reporting LATE estimates do not provide systematic evidence that there is substantial heterogeneity across different ability levels in...

We characterize the bias of propensity score based estimators of common average treatment effect parameters in the case of selection on unobservables. We then propose a new minimum biased estimator of the average treatment effect. We assess the finite sample performance of our estimator using...