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st: Observation number in fixed effect regression


From   "Hui Wang" <jackie_stata@hotmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Observation number in fixed effect regression
Date   Thu, 19 Oct 2006 14:17:21 +0000

Hi all,

I want to run the following regression:

Y = pai0 + pai1*A+X*pai2+e

Each observation is a kid in certain households. 'A' is the variable I am interested in; "X" is a vector of other controls. There are totally 1100 kids. Some of them are siblings in the same houshold. The number of kids who have siblings in the dataset is about 200. If I run the following command in stata:

xtreg Y A X , fe i(id)

where id is the houshold ID. I should expect the stata to explore the variation within the households with multiple kids to estimate pai1. That says, the observation number should be about 200. But in the results, stata report that the number of observation is actually about 1100 (the whole sample).

Why is that? Is there any way to correct this? I found that the same problem does not happen to logit regression (xtlogit).

Thanks,

Jackie

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