From: Marc Girondot <marc.girondot_at_ese.u-psud.fr>

Date: Wed 15 Jun 2005 - 15:27:53 EST

Date: Wed 15 Jun 2005 - 15:27:53 EST

>Dear all R-users,

*>
**>I am a new user of R and I am trying to build a discrete choice model (with
**>more than two alternatives A, B, C and D) using logistic regression. I have
**>data that describes the observed choice probabilities and some background
**>information. An example below describes the data:
**>
**>Sex Age pr(A) pr(B) pr(C) pr(D) ...
**>1 11 0.5 0.5 0 0
**>1 40 1 0 0 0
**>0 34 0 0 0 1
**>0 64 0.1 0.5 0.2 0.2
**>...
*

You can use multinom()

Here is an exemple

For example let this matrix to be analyzed: male female aborted factor

10 12 1 1.2 14 14 4 1.3 15 12 3 1.4

The data are to be entered in a text file like this:

output factor n

m 1.2 10 f 1.2 12 a 1.2 1 m 1.3 14 f 1.3 14 a 1.3 4 m 1.4 15 f 1.4 12 a 1.4 3

library(MASS)

dt.plr <- multinom(output ~ factor, data=dt, weights=n, maxit=1000) dt.pr1<-predict(dt.plr, , type="probs") dt.pr1

>I have been able to model a case with only two alternatives "A" and "not A"

*>by using glm().
**>
**>I do not know what functions are available to estimate such a model with
**>more than two alternatives. Multinom() is one possibility, but it only
**>allows the use of binary 0/1-data instead of observed probabilities. Did I
**>understand this correctly?
**>
**>Additionally, I am willing to use different independent variables for the
**>different alternatives in the model. Formally, I mean that:
**>Pr(A)=exp(uA)/(exp(uA)+exp(uB)+exp(uC)+exp(uD)
**>Pr(B)=exp(uB)/(exp(uA)+exp(uB)+exp(uC)+exp(uD)
**>...
**>where uA, uB, uC and uD are linear functions with different independent
**>variables, e.g. uA=alpha_A1*Age, uB=alpha_B1*Sex.
**>
**>Do you know how to estimate this type of models in R?
*

I don't think it is possible... (at least simply, without writing all the script !)

Note that I don't undrestand where the residual deviance from multinom() come from. I cant find the logic.

Marc

-- __________________________________________________________ Marc Girondot, Pr Laboratoire Ecologie, Systématique et Evolution Equipe de Conservation des Populations et des Communautés CNRS, ENGREF et Université Paris-Sud 11 , UMR 8079 Bâtiment 362 91405 Orsay Cedex, France Tel: 33 1 (0)1.69.15.72.30 Fax: 33 1 (0)1 69 15 56 96 e-mail: marc.girondot@ese.u-psud.fr Web: http://www.ese.u-psud.fr/epc/conservation/Marc.html Skype: girondot Fax in US: 1-425-732-6934 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.htmlReceived on Wed Jun 15 15:31:07 2005

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