Re: st: nlogitrum and nlogit: unbalanced data

[John Fulton <fulton@ssc.wisc.edu>]

> Richard Gates suggested modifying nlogitrum to remove a trap
Dear Richard,
Thank you very much. 
Does nlogitrum call the current version of nlogit, subject to the trap?  
Or does nlogitrum have access to an older version of nlogit, somehow?
In other words, is there anything I would be giving up by going with 
nlogitrum's version of nlogit?
I'm obviously thinking of "inside-Stata" stuff, like speed increases 
since 7, for example, or something else that might not show up in the 
nlogit version changelogs?

Because I could (at least in principle) use the Koppelman-and-Wen 
constraint of equality of IV parameters to produce a RUM-consistent 
estimation.

Again, thank you very much,
John.

references:
nlogitrum: Heiss, "net sj 2-3 st0017", though you could "search nlogitrum".
K+W:  Transportation Research. B, Vol. 32, No. 5, pp. 289-298, 1998
also see Hunt, Journal Of Regional Science, Vol. 40, NO. 1,2000, pp. 89-113)




> John Fulton is inquiring about the "unbalanced data" error message from
> -nlogitrum-.
>
> There is an error trap in -nlogitrum- to check that the alternatives for each
> case (individual) are balanced.  This error trap is unnecessary.  The code in
> -nlogitrum- is based on the Stata 7 release of -nlogit-.  Since then we 
> (at StataCorp) have determined the restriction that each case must have the
> same set of alternatives is unnecessary and we have removed it from -nlogit-.
>
> John, if you are feeling up to a bit of programming you can copy nlogitrum.ado
> to your working directory and modify it.  You can find where -nlogitrum-
> resides using the stata command
>
> . which nlogitrum
>
> It is probably in your personal ado directory. 
> You will see in the ado code a call to the local program -ChkDta- on line 78.
> Comment out this line.  
> Your ado path will have the working directory ahead of the personal directory.
> To check your ado path use
>
> . adopath
>
> Clear the original version of -nlogitrum- from memory using
>
> . program drop _all
>
> then try running your model again.
>
> Alternatively, you could copy nlogitrum.ado to mynlogitrum.ado and
> change the program name within the file to mynlogitrum.ado.  
> Be sure to constrain the inclusive-valued (dissimularity) parameters to 1
> for the degenerate nests in the RUM model otherwise you will not get 
> convergence.  I do not believe the IV parameters exist for the RUM
> model in this case.  They are identifiable in the Nonnormalized model
> if you have an alternative specific variable (maybe var1 in your model
> specification). 
>
> Best Regards
>
> -Rich
> rgates@stata.com
> *
> *   For searches and help try:
> *   http://www.stata.com/support/faqs/res/findit.html
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
>   
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/