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Re: st: help of levpet

From   "Brian P. Poi" <>
Subject   Re: st: help of levpet
Date   Wed, 2 Dec 2009 09:20:38 -0600 (CST)

On Wed, 2 Dec 2009, Zhang Yan wrote:

I am Zhangyan, a PhD candidate in Economics.
I am using levpet to calculate TFP. But stata said
. tsset frdm year
      panel variable:  frdm (unbalanced)
       time variable:  year, 2005 to 2007, but with gaps
               delta:  1 unit

. levpet lnva, free( lncyry lnage) proxy( lnzjtrj) capital(lngdzch) valueadded i
(frdm) t(year) reps(250)
repeated time values within panel

If Zhangyan would send the dataset directly to me (, I'd be happy to look into the cause of this error message.

However, note that here the dataset has only three time periods, with
gaps. I strongly suspect that with very short panels together with gaps in the data, -levpet-, -opreg-, and similar productivity estimators will
produce very imprecise estimates.

   -- Brian Poi

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