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Re: st: help of levpet


From   "Brian P. Poi" <bpoi@stata.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: help of levpet
Date   Wed, 2 Dec 2009 09:20:38 -0600 (CST)

On Wed, 2 Dec 2009, Zhang Yan wrote:


Dear
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
r(451);
"


If Zhangyan would send the dataset directly to me (bpoi@stata.com), 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
   -- bpoi@stata.com

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