Justina,
Are you sure the weights are equal? It looks like -xtgee- performs
(xtgee.ChkWt) the following to check if the weights are equal:
- cap by `ivar': assert `v'==`v'[_n-1] if _n>1
- if _rc {
- noi di in red "weight must be constant within `ivar'"
- exit 199
}
I am not sure why it would issue the error if they were equal.
Scott
________________________________________
From: [email protected]
[mailto:[email protected]] On Behalf Of
[email protected]
Sent: Wednesday, December 15, 2004 3:56 PM
To: [email protected]
Subject: st: xtgee and weights
Dear Statalisters,
I am trying to use the xtgee command for an international panel and weight
my observations according to the population in a country. The weights should
correct for heteroscedasticity.
Having read in the manual that weights should be constant within panel, I
have chosen the reverse square root of the population of the year 1992 as a
weight for the whole time range and created an according variable which
takes the same value for each year (only differing between countries).
However, trying to run:
xtgee y x1 x2 x3 .... yeardummies [iw = weight], robust corr(ar3)
family(gauss) link(ident)
resulted in the message
weight must be constant within country_id
r(199);
The problem is: my weights are constant with a country ! (The problem is
independent of the use of pweight instead)
Does anybody have a glimpse of where the mistake could be ?
Thanks a lot in advance,
Justina
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