st: conditional and mixed logit

[Shehzad Ali <sia500@york.ac.uk>]

Hi listers,

I am using conditional and mixed logit models for discrete choice data 
(-clogit- and -mixlogit-). The demographic characteristics like age, sex, 
education etc obviously do not vary for the same respondent. When I use 
them the following model, Stata drops the demographic variables from the 
model.

clogit choice length frequency benefit age sex education, group(n)

Error message: age omitted due to no within-group variance. (same message 
for sex, education etc.)

Its understandable that since demographic variables do not vary within each 
a choice set (n) the demographic variables will not be allowed. But these 
variables do vary between individuals and I want to account for that. Can I 
use mixed logit model for this purpose?

When I use the following -mixlogit- command, I get "comformability error". 
Can anyone please suggest why and whats the best way to accommodate 
demographic variables in the model?

mixlogit choice, group(n) id(id) rand(length frequency benefit age sex 
education)

Here id is unique for each individual and n is unique for each choice set.

Any help would be greatly appreciated.
Thank you,
Shehzad


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