This paper gives a short overview of Monte Carlo studies on the usefulness of Heckman's (1976, 1979) two-step estimator for estimating a selection model. It shows that exploratory work to check for collinearity problems is strongly recommended before deciding on which estimator to apply. In the...

This paper gives a short overview of Monte Carlo studies on the usefulness of Heckman's (1976, 1979) twostep estimator for estimating a selection model. It shows that exploratory work to check for collinearity problems is strongly recommended before deciding on which estimator to apply. In the...

I demonstrate that Ai and Norton's (2003) point about cross differences is not relevant for the estimation of the treatment effect in nonlinear "difference-in-differences" models such as probit, logit or tobit, because the cross difference is not equal to the treatment effect, which is the...