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Re: st: How to analyze repeated cross-sectional data in which units are not truly followed?


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: How to analyze repeated cross-sectional data in which units are not truly followed?
Date   Mon, 19 Oct 2009 20:38:39 +0000 (GMT)

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://www.maartenbuis.nl
--------------------------


--- On Mon, 19/10/09, Misha Spisok wrote:
> In brief, are -xt- commands appropriate for repeated
> cross-sectional data in which different units are observed
> over time?  For the data below, I considered the following:
<snip>
> . egen newerid = group(state year type)
> . xtset newerid year
> . xtreg y x1 x2 [fw=n], fe
<snip>
> The third "error" is that I get something like the
> following for output:
>      x1      | 
> (dropped)
>      x2      | 
> (dropped)

This is as it should be: You basically added dummies for state,
year, and every possible combination of your explanatory 
variables. As a consequence there is no variation left for your
explanatory variable to explain, and they are dropped.

> What is the appropriate way of analyzing repeated
> cross-sectional data in which different units are observed
> in each period (in general) and, in particular, grouped 
> cross-sectional data of the variety that I have (where the
> same units are probably observed, but they are not uniquely
> identified and cannot be followed in the sense of panel
> data with a unique identifier)?

I would just use -regress- with fweights and dummies for State
and year. This way you can't use the fact that the same persons
are measured twice, but if it is not in the data, than that is 
the end of the story. 

Hope this helps,
Maarten

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