[Limdep Nlogit List] Latent class problems

[Soren Olsen]

Dear all,

I'm experiencing some problems with a latent class model:

NLOGIT ;lhs=choose
;choices=1,2,3
;Rhs=catch_m,catch_h,size_m,size_h,nat_m,nat_h,qua_m,qua_h,dist_m,dist_h,num_m,num_h,p,optout
;LCM
;Prob=prob
;parameters
;maxit=200
;pds=6
;pts=2 $
 
My problem is that when I specify two classes as above, I get the following error message (though it does produce some results, I guess I shouldn't trust them):
Error 806: (The log likelihood is flat at the current estimates.)

When I use three classes (pts=3), I get another error message (and no results produced):
Error 1027: Models - estimated variance matrix of estimates is singular

However, when I use four classes (pts=4), it runs nicely and produces results that make very good intuitive sense, and everything looks ok.

With five classes (pts=5), I again get the following message:
Error 1027: Models - estimated variance matrix of estimates is singular
 
Now, I guess I actually have two questions:
1) Should I trust the results that I get with four classes? 
2) Why wont the other models run?

I should add that I have run RPL and EC models on exactly the same data and using the same utility function without any problems, so I guess my dataset is set up as it should be. I have tried specifying the utility functions using the model statement, but this didn't help

Any suggestions and help is much appreciated.

Regards
Søren

__________________________________________________
Bruger du Yahoo!?
Er du træt af spam?  Yahoo!Mail har den bedste spambeskyttelse, der findes 
http://dk.mail.yahoo.com