Dear Statalisters,
I'm estimating a cost efficiency frontier with panel data in Stata 9 using:
xtfrontier [depvar] [indepvar], tvd cost.
My estimate for eta is significant.
The resulting efficiency scores do vary with time if I use
predict newvar, te.
But the results DO NOT vary with time if I use
predict newvar, u or predict newvar, m.
I don't understand why, because according to the formulas in the manual (XT, p.76) eta should be taken into account in both cases. I need the values of u to calculate the efficiency relative to the best firm in the sample rather than to the cost function.
Has anybody encountered such problems? Where is my mistake if there is any?
Thank you very much in advance!
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