[Limdep Nlogit List] start=logit with NL

[Kandice L. Kleiber]

Dr. Greene -

Thank you for your quick response!

When I run the program (and I adjusted the IVSET command to brackets),  
the output still does not show the starting values.  I guess I'm not  
clear as to whether or not the program should ALWAYS show starting  
values (when running a nested logit model)?  I get slightly different  
results when I put start=logit than when I do not.  I guess to be on  
the safe side, I should always include the start command?

Also when I use the command RU2, the reported IV parameter, μ, is  
greater than 1 (which makes sense because then the *real* IV parameter  
is (1/μ) since λ=1 and then (λ/μ)<1).  But when I use RU1 with  
IVSET: (wh,ot)=[1.0], I should receive a reported IV parameter, λ,  
with λ<1  (since μ=1 and assuming I change nothing else) ...  
correct?  However I keep receiving values >1 with RU1.

I guess I'm not sure what is happening, since they should just be  
inverses of one another?  Any ideas?

Thanks again -
Kandice.



On Jul 9, 2009, at 12:19 PM, William Greene wrote:

> Kandice: Whether an MNL starting value is computed is independent
> of the setting of RU1 vs. RU2. (At least it is according to the
> internal program code.) You should not have to add ;Start=Logit
> to the command. However, that will do no harm; the program should
> always compute the initial MNL model. There is no other place to
> get starting values. I can't say I can come up with a reason why
> the MNL results were not reported.  On your ;IVSET instruction,
> you should use IVSET:(...)=[1] to force the value to equal one. I.e,
> include it in square brackets. Otherwise it is just a starting value.
> The program reports mu, not 1/mu.
> /Bill Greene
>
>
>
>
> ----- Original Message -----
> From: "Kandice L. Kleiber" <kleiberk at onid.orst.edu>
> To: "Limdep and Nlogit Mailing List" <limdep at limdep.itls.usyd.edu.au>
> Sent: Thursday, July 9, 2009 2:26:31 PM GMT -05:00 US/Canada Eastern
> Subject: [Limdep Nlogit List] start=logit with NL
>
> Hi -
>
> I have a few questions regarding the *black box* in NLOGIT.  The
> nested logit model I have been running looks like this:
> tree = cs(corn,soy), wh(wheat), ot(other), and the data does NOT very
> across alternatives - only across observations.
>
> Because my nested model is a partially degenerate model, I'm using the
> RU1/RU2 commands to normalize.  When I use RU1, I add the restriction
> IVset:(wh,ot)=1.0.  However, when I run the 2 models, they "run"
> differently.  RU1 begins by running a MNL to get starting values,
> while RU2 does not, unless I call start=logit (at least not
> explicitly).  Even when I use the start=logit command on RU2, the
> value of my log likelihood function differs between RU1 and RU2 - from
> what I understand, this value should be the same (given the
> restriction with RU1).
>
> Should I always include the start=logit command?  If not, when  
> should I?
> When the command RU2 is used, is the IV parameter NLOGIT reports = (1/
> μ)?  Or does it report μ?
>
> code:
> nlogit;
> shares;
> tree = cs(corn,soy),wh(wheat),ot(other);
> lhs = lev;
> choices=corn,soy,wheat,other;
> ru2;  /*or ru1 with restriction ivset:(wh,ot)=1.0*/
> model:
> U(corn) = c_c+c_price*price+ ... /
> U(cs) = cs_cs+cs_soil*soil+.../
> U(wheat)=w_w+w_soil*soil+...$
>
> Any help is appreciated!  Thank you!
> Kandice.
>
> ---
> Kandice L. Kleiber
> Graduate Teaching Assistant
> Department of Economics
> Oregon State University
> e: kleiberk at onid.orst.edu
> w: 541.737.6628
>
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---
Kandice L. Kleiber
Graduate Teaching Assistant
Department of Economics
Oregon State University
e: kleiberk at onid.orst.edu
w: 541.737.6628