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Re: st: RE: re: nlogitrum


From   "Flora Au" <fau@ucalgary.ca>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: re: nlogitrum
Date   Thu, 5 May 2005 09:33:28 -0600 (MDT)

Thank you Nick. To make the issue that I am facing a bit more clear, I
first started with a conditional logit model and tested for IIA (which I
also used the old fashion hausman command to double check). As a result,
my model failed the IIA, then I test my model with a nested logistic model
'nlogit'. However, I got the same result as my 'clogit' model, so my
colleague suggested to used the 'nlogitrum' instead. By what I describe
above, could anyone tell me why I have the same results using -clogit- and
-nlogit- ?

Thank you again,
Flora

Nick Cox said:
> This was previously posted on 28 April
> and got no replies.
>
> Why not? I guess because only a few
> kinds of rather basic comment seem possible.
>
> First, it is possible that your data
> are not suitable for this model.
> You need to think about that.
>
> Second, -nlogitrum- offers handles for
> varying the maximization process in using
> -ml- to fit the model, particularly important
> when defaults run into problems. Those are documented
> and explained in various standard places, e.g.
> documentation on -ml- and the Gould and
> friends book on the same area of Stata.
>
> Nick
> n.j.cox@durham.ac.uk
>
> Flora Au
>
>> I am having problem with NLOGITRUM.
>>
>> This the the command I am using to run the model:
>>
>> nlogitgen branch = alt(package:1|2, nopack:3)
>> nlogittree alt branch
>> nlogitrum pref nurse nsq na2 na3 n_nt1st n_highedu homevis
>> visitsq va2 va3
>>  hv_nt1st hv_highedu nhv homehelp helpsq cost c_highinc, group(indid)
>>  nests(alt branch)
>>
>> The first two command ran fine, however the last command result in an
>>  error message which is written as follow:
>>
>> could not calculate numerical derivatives
>> flat or discontinuous region encountered
>>
>> Can you assist me as to how to fix this model?
>
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