This paper considers a panel data model with time-varying individual effects. The data are assumed to contain a large number of cross-sectional units repeatedly observed over a fixed number of time periods. The model has a feature of the fixed-effects model in that the effects are assumed to be...

We wish to test whether technical inefficiency depends on observable characteristics of the firm. We consider a two-step procedure in which the second step is a regression of estimated inefficiency on firm characteristics. A valid test of the hypothesis of no effect requires an adjustment to the...