With a fixed effects model you are only using information from changes
within a unit, instead of also comparing differences across units. If
you have only one observation per unit, you don't have any information
on changes within a unit.
-- Maarten
--- "jenny.montaldo" <[email protected]> wrote:
> Dear all,
>
> I have a panel of regional data for ten years. I want to instrument a
> variable and apply xtivreg, fe. However I have an instrument very old
> that is only available for one year. Hence, I thought it was possible
> to perform such an estimation, since the first stage regression gives
> different fitted values (of course,since the variable to be
> instrumented changes with time). However when I run such a
> regression, stata says that the regression is not identified. I tried
> also to perform myself the first step, that, as I supposed, gives
> different values for each year. But then, when I perform the fixed
> effects estimation with such fitted values, it drops them.
> May anyone help me to understand why?
> Many thanks
> jenny
>
>
>
> *
> * For searches and help try:
> * http://www.stata.com/support/faqs/res/findit.html
> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/
>
-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands
visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434
+31 20 5986715
http://home.fsw.vu.nl/m.buis/
-----------------------------------------
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*
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