--- In statalist, Claire Johnstone wrote:
> Dear Stata-users, I have 2 queries re. Conditional Logit (I've searched
> online help & don't have a manual). These are:
> 1. Is there a maximum number of alternatives you can have in a choice
> set?
As long as -clogit- is the same as -xtlogit-, the question can be restated
as "What is the maximum number of observations per panel?", and you can
find that in -help limits- to be the maximum matsize (800 for Intercooled,
11K for SE).
> 2. Can you have multiple positive responses to alternatives in a single
> choice set?
Again, as long as you can have multiple 1's in the panel setting, this
should work for the regular -clogit-, too. By trial and error,
. clogit for pri, group(rep)
note: multiple positive outcomes within groups encountered.
note: 2 groups (10 obs) dropped due to all positive or
all negative outcomes.
Iteration 0: log likelihood = -23.108062
Iteration 1: log likelihood = -23.107154
Conditional (fixed-effects) logistic regression Number of obs = 59
LR chi2(1) = 0.00
Prob > chi2 = 0.9660
Log likelihood = -23.107154 Pseudo R2 = 0.0000
------------------------------------------------------------------------------
foreign | Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
price | 5.58e-06 .0001307 0.04 0.966 -.0002507 .0002618
------------------------------------------------------------------------------
all Stata does is it notes to you that there are multiple positive
outcomes, but does not halt on that.
As for the weights question, I don't think there is any way around it
except for explicitly -expand-ing your data, so if you really have tons of
implied observations under [fw], you might be in trouble as regarding the
number of observations per panel / choice set.
--- Stas Kolenikov
-- Ph.D. student in Statistics at UNC-Chapel Hill
- http://www.komkon.org/~tacik/ -- [email protected]
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