[Limdep Nlogit List] Poisson model with truncated data
Martin Chun Qiu
cqiu at ualberta.ca
Sat Feb 18 04:52:20 EST 2006
Hi
I am wondering if anybody has an idea how to impose a constraint on the dependent variables in a Poisson model. I am studying online browsing patterns of a certain group of people who can visit the maximum 14 pages. The dependent variables are demographic variables. I guess I have to treated it as a truncated dataset, but how to do it?
Any thoughts are greatly appreciated.
Martin Qiu
School of Business
University of Alberta
======= 2006-02-17 10:39:34 Your message=======
>Dear Branca: As the manual explains, that crosstab is computed as the sum
>of p(i) * d(i)' where p(i) is the vector of predicted probabilities and d(i) is a vector
>of zeros save for a one placed in the position of the individual's choice. If you
>have choice specific constant terms in the model, then by construction, for an MNL
>model, this method will match the totals on the diagonals of the matrix. It is
>implied by the first order conditions for computation of the coefficients. If you
>replaced p(i) with some vector or "predictions" which contained some kind of
>predicted outcome - thereby a one in the position of the prediction and zeros
>elsewhere, then computed the table in the same way, you would get the outcome
>you appear to be expecting. But, this requires you to define the d^(i). Whatever
>method you use, it will be arbitrary. NLOGIT does not show any preference on
>this score - there is no natural prediction. The ;LIST parameter will produce a
>listing in which the "prediction" is the cell with the largest probability. You could
>use this. This is something that you, yourself, can program, however, it is not
>done automatically within the software.
>Sincerely,
>Bill Greene
>
>************************************************
>Professor William Greene
>Department of Economics
>Stern School of Business
>New York University
>44 West 4th St., Rm. 7-78
>New York, NY 10012
>Ph. 212.998.0876
>Fax. 212.995.4218
>URL. http://www.stern.nyu.edu/~wgreene
>Email. wgreene at stern.nyu.edu
>************************************************
>
>----- Original Message -----
>From: Branka Valcic <ffbv at uaf.edu>
>Date: Friday, February 17, 2006 2:45 am
>Subject: [Limdep Nlogit List] Crosstab command for logit
>
>> Greetings,
>>
>> I am trying to get a cross-tabulation of actual versus predicted
>> outcomes for each alternative in a multinomial logit. It seems to
>> me
>> that ;Crosstab command in NLOGIT should do the trick. The
>> resulting
>> table, however, shows for each alternative total row equal total
>> column,
>> which, if I am correctly interpreting the table means that for
>> each
>> alternative the model predicts 100% of the actual outcomes! It is
>> very
>> hard for me to believe this so I must wonder if I am
>> misinterpreting the
>> table. Would someone please enlighten me on this issue?
>>
>> Best regards,
>> Branka Valcic
>>
>> ------------------------
>> Branka Valcic
>> Assistant Professor
>> Economics Program
>> School of Management
>> University of Alaska Fairbanks
>> P.O. Box 756080
>> Fairbanks, Alaska 99775-6080
>>
>> Phone: (907) 474 2754
>> Fax: (907) 474 5219
>> URL: www.faculty.uaf.edu/ffbv
>> -------------------------
>>
>>
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>
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