SFPANEL: Stata module for panel data stochastic frontier models estimation

The official Stata -xtfrontier- command allows the estimation of a Normal-Truncated Normal model with time-invariant inefficiency (Battese and Coelli 1988) and a time-varying version, named as time decay model, proposed by Battese and Coelli (1992). -sfpanel- allows to estimate a wider range of time-varying inefficiency models including the Cornwell et al. (1990) and Lee and Schmidt (1993) models, the flexible model of Kumbhakar (1990), the time decay and the inefficiency effects models of Battese and Coelli (1992, 1995) and the true fixed and random-effects models developed by Greene (2005). For the last two models, -sfpanel- allows different distributional assumptions, providing the modeling of both inefficiency location and scale parameters. Furthermore, the command allows the estimation of the random-effects time-invariant inefficiency models of Pitt and Lee (1981) and Battese and Coelli (1988), as well as the fixed-effects version of the Schmidt and Sickles (1984) model, characterized by no distributional assumptions on the inefficiency term. In addition, since the main objective of the stochastic frontier analysis is the estimation of inefficiency, we provide a post estimation command to compute (in)efficiency scores, as well as their confidence intervals (Jondrow et al. 1982; Battese and Coelli 1988; Horrace and Schmidt 1996). Finally, -sfpanel- allows also the simultaneous modeling of heteroscedasticity in the idiosyncratic error term.