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...

We present a new and simple empirical methodology to identify relative wage rigidity dynamics. The methodology is applied to data from the Polish Labour Force Survey for the period 1994 to 1998. We estimate ceteris paribus changes in relative wage and unemployment differentials for various...

We analyse the Polish wage and unemployment structure between 1992 and 1995 on the basis of the Polish Labour Force Survey. It is shown that within this period wage inequality has stabilised. Surprisingly, wage inequality is lower in the private than in the public sector. Our test results show...

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...