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st: "xtfrontier" vs. "frontier, d(t)" with panel data
I'm pretty new to the subject of stochastic frontier models and from
the STATA reference texts I didn't quite understand what exactly the
panel specific difference is that an xtfrontier estimate generates
compared to a simple pooled estimate using frontier, d(t) when applied
to panel data.
For an experiment of comparison I applied frontier, d(t) and xtfrontier
to a set of panel data. the estimates tend to differ more than i
expected, and in the frontier, d(t) case the standard errors tend to be
To me it seemed from the text that the only difference is that
xtfrontier treats the inefficiency-term uniformely over a group, whereas
frontier treats it separately for each observation - might this be
responsible for the difference, or do I miss some (possibly completely
obvious ;-)) fact?
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