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st: panel normalisation before xtgee


From   Allison.Milner@student.griffith.edu.au
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: panel normalisation before xtgee
Date   Tue, 31 Mar 2009 16:59:23 +1000

Dear Statalist,

I am using xtgee (xtgee, f(nb) corr(ar1) vce(r)) to analyze an unbalanced panel data set (with 73 countries, 1980-2006). Someone suggested that I normalize my variables by subtracting the mean from each of my observations. 
e.g. 
YEAR        VARIABLE ONE
year 1980  observation 1 for variable 1 - mean of observation of variable 1
year 1981  observation 2 for variable 1 - mean of observation of variable 1
year 1982  observation 3 for variable 1 - mean of observation of variable 1

Is this necessary?  
Any opinions on this subject would be great.
Allison
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