Dear Users,

I am currently using NLOGIT to estimate a random parameter logit. Does anyone know whether the p-values attached to the standard deviation = estimates adjust for the fact that this is a positive quantity? Or, = should we not worry about it? Many thanks best wiji

[此贴子已经被作者于2005-9-18 2:02:12编辑过]

1. How to get the SP-RP scale parameter for logit model calibrate with RP & SP data? (2)

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Date: Wed, 7 Sep 2005 09:47:55 +0800 From: Susanna Tam <susanna.tam@POLYU.EDU.HK> Subject: How to get the SP-RP scale parameter for logit model calibrate with RP & SP data?

Anybody know how to run a multinomial logit model using RP and SP data? Did the SP-RP scale parameter run out automatically, or I need to write some commands to get it? Anyone can help? Many thanks.

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Date: Tue, 6 Sep 2005 22:11:27 -0400 From: Fred Feinberg <feinf@UMICH.EDU> Subject: Re: How to get the SP-RP scale parameter for logit model calibrate with RP & SP data?

Susanna Tam wrote:

Anybody know how to run a multinomial logit model using RP and SP data? Did the SP-RP scale parameter run out automatically, or I need to write some commands to get it? Anyone can help? Many thanks.

We do this all the time in LIMDEP, but not in a very elegant way. Because the 'coefficient' of the Gumbel error in standard logit is fixed to one, what you really want to do is say that, say, the RP error coefficient is 1 (standard logit), and the SP coefficient is some number you wish to estimate. A simple, brute force way to do this is to write a batch job to divide all your SP data by a variety of values, and run a logit model on your SP data and RP data together. Because this is a discrete choice model, dividing all your data by some value is the same as multiplying your error by that value. Monitor the LLs until you get the optimum divisor, and that's your scaling factor. You can then do a likelihood ratio test against the logit run with no scaling to assess significance.

My co-author Linda Salisbury (who did this in her dissertation) and I have done this hundreds of times, and it's only failed to converge maybe twice. Logit runs very fast, so running a batch job is no problem. You can usually estimate the scale parameter and run all tests in a few minutes, and the likelihood ratio test is preferred econometrically to looking at asymptotic t-like values from the logit output itself.

There is probably a simpler way to do this using an HEV model, but I don't see how to get around manual scaling.

Fred

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Prof. Fred Feinberg Stephen M. Ross School of Business University of Michigan feinf@umich.edu

[此贴子已经被作者于2005-9-18 2:03:43编辑过]

Hello list,

I'm trying to run a panel model, and test for fixed/random effects, and I get the error: Could not invert VC matrix for Hausman test. I'm assuming this is because the VC matrix is singular, or close to it? I've printed it, looked at it, and don't see anything obvious. Is multicollinearity the likely culprit, or is there some other obvious thing I should be looking at?

Many thanks in advance for advice,

Darla Munroe

Hello,

Singularity is probably the problem. One possibility is to rescale your variables. I ran into a similar situation when analyzing experimental data. I rescaled my variables (e.g. lab dollars to actual dollar earnings) and was able to run the test.

Good luck,

Chris McIntosh