I'm not sure if the answers your question, but ... the quote below is from
Wooldridge "Econometric Analysis of Cross Section and Panel Data" page 266.
"In panel data analysis, the term 'time-varying explanatory variables' means
that each element of x(it) varies over time for some cross section units. Often
there are elements of x(it) that are constant across time for a subset of the
cross section. For example, if we have a panel of adults and one element of
x(it) is education, we can allow education to be constant for some part of the
sample. But we must have education changing for some people in the sample."
Scott
----- Original Message -----
From: "Guillaume Frechette" <[email protected]>
To: <[email protected]>
Sent: Saturday, October 19, 2002 3:35 PM
Subject: st: FE and groups w/out variation
> Dear Statalisters: I thought I read on the list not so long ago someone who
> said that when estimating FE one shouldn't drop groups that do not have
> variation (I looked for it in the archive but couldn't find it). Did I
> invent this? At any rate, could someone tell me what is the 'best'
> procedure, keeping all groups or only the ones that have variation, and what
> is the logic for the answer. I would also appreciate it if someone could
> point me to a book or article that spells this out in writing.
>
> Thanks in advance,
>
> g
>
>
>
>
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