Heckman’s (1976, 1979) sample selection model has been employed in many studies of linear or nonlinear regression applications. It is well known that ignoring the sample selectivity problem may result in inconsistency of the estimator due to the correlation between the statistical errors in...

This paper primarily reviews the panel stochastic frontier (SF) model in which the composite error term εit has four components, i.e. εit=τi−ηi+vit−uit, where ηi and uit are the persistent and transient inefficiency components, τi is the random firm effect and vit is the random noise....

Heterogeneity among firms has been an important issue in studying firms’ technical efficiencies. If firms do not randomly fall into different groups with different technologies but by self-selection, statistically it implies the data are subject to the sample selection bias. In this paper, we...