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st: help levpet

From   pim de Nijs <>
Subject   st: help levpet
Date   Thu, 11 Dec 2008 17:29:57 +0100

My knowledge about Stata is limited and a feel ashamed that i have to bother you with my question because maybe I just made a stupid mistake in the command that I use. But I really do not know how I can solve the problem and I could not find a solution on the internet.  
I want to use the following command:
. levpet logSales, free(logEmployees ) proxy(logMaterials) capital(logCapital) i(number) t(Year) revenue 
I get the following error:
repeated time values within panel

I have no idea why i get the ''repeated time values within panel'' error. I am 100% sure that there are no duplicates:
. dupliactes list Year number
result: no observations are duplicates
By only using a part of my dataset i get an idea what the problem is:
. levpet logSales if (NACE<=1531), free(logEmployees ) proxy(logMaterials) capital(logCapital) i(number) t(Year) revenue 
Now I get the results of the levpet command. However there is something strange:

Dependent variable represents revenue.          Number of obs      =       148
Group variable (i): number                                   Number of groups   =      5756
Time variable (t): Year
                                                               Obs per group: min =         1
                                                               avg =       4.1
                                                               max =         5

The number of observations is 148 and the number of groups is 5756? Then I see that the average number of observations per group is 4.1 This means that the number of groups should be 36 and not 5756.
I really have know idea what is going wrong. I just like to get the levpet results for my whole dataset. The . help levpet command do not give me the answer. Others papers that I have read and that are using the levpet command are telling that it is straightforward to use the levpet command. 
Can someone help me
Yours sincerely
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