<>
Actually, Stata complains whether you enter "va" or its log into -clogit-: "
note: ... omitted because of no within-group variance." It would be weird
for the log transform to change the effect of va as the transform itself
cannot generate any variance within the groups.
The problem is mentioned in [R]clogit, p. 284.
*************
clear*
inp double siren va str10 country tax double GDP choice
17251067 94997 Spain .35 777000000000 1
17251067 94997 Brazil .34 486000000000 0
17251067 94997 Italy .38 1330000000000 0
17251068 28142 Brazil .34 486000000000 1
17251068 28142 Spain .35 777000000000 0
17251068 28142 Italy .38 133000000000 0
17251069 75758 Italy .38 13300000000 1
17251069 75758 Spain .35 777000000000 0
17251069 75758 Brazil .34 486000000000 0
end
l, noo sepby(va)
g lntax=log(tax)
g lnGDP=log(GDP)
encode country, gen(newcountry)
drop country
rename newcountry country
* w/o va
clogit choice country lntax lnGDP , group(siren) iter(10) nolog
*with va
clogit choice country lntax lnGDP va, group(siren) iter(10) nolog
g lnva=log(va)
*with ln(va)
clogit choice country lntax lnGDP lnva, group(siren) iter(10) nolog
*************
Might -asclogit- be a way out for Isabelle?
HTH
Martin
-----Ursprüngliche Nachricht-----
Von: [email protected]
[mailto:[email protected]] Im Auftrag von
[email protected]
Gesendet: Freitag, 27. März 2009 09:42
An: [email protected]
Betreff: st: conditional logit problem
Dear statalisters,
I have a dataset with firms, to which is attributed a number called
"siren", and characteristics of thses firms (exportations, size, value
added...). I have too the country in which they decide to invest, and
characteristics of this country (GDP, population, tax rate, labor
costs...)
So my database looks like this (it is an example with 3 firms which choose
one unique country):
siren va country tax GDP choice
17251067 94997 Spain .35 7.77e+11
1
17251067 94997 Brazil .34 4.86e+11
0
17251067 94997 Italy .38 1.33e+12 0
3.025e+08 28142 Brazil .34 4.86e+11 1
3.025e+08 28142 Spain .35 7.77e+11 0
3.025e+08 28142 Italy .38 1.33e+12 0
3.026e+08 75758 Italy .38 1.33e+12 1
3.026e+08 75758 Spain .35 7.77e+11 0
3.026e+08 75758 Brazil .34 4.86e+11
0
When I run a conditional logit with only countries'characteristics as
regressors (***clogit choice country lntax lnGDP, group(siren)**, where
lntax and lnGDP are the log of tax and GDP), it is OK.
But what I don't understand is this point:
-When I add value added as a control variable (***clogit choice country
lntax lnGDP va, group(siren)***), it works, even if the coefficient for va
is strange.
-When I add the log of value added as a control variable ((***clogit
choice country lntax lnGDP lnva, group(siren)***), STATA refuses to
provide results and write:"outcome does not varies in any group".
So I wonder why it is ok in a case and not in the other else which is very
similar, and I don't know what kind of logit to run which allows me to mix
the two types of variables.
Thank you very much for help,
Isabelle
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