
I tried the following ordered logistic regression in R:

mod1 <- polr(altitude~sp + wind_dir + wind_speed + hr, data=altioot)

But when I asked The summary of my regression I got the folloing error message:

> summary (mod1)

Re-fitting to get Hessian

Error in optim(start, fmin, gmin, method = "BFGS", hessian = Hess, ...) : 
        the initial value of 'vmin' is not finished.

I decided to try it in SAS with the following program:

PROC LOGISTIC
DATA=altioot;
CLASS sp wind_dir ;
title "mod1";
output out=mod1;
MODEL altitude = sp wind_dir wind_speed hr;
RUN;

And it ran well with an good output.  So my question is: Can someone tell me what is the difference between the ordered logistic regression of R and that of SAS?  Does anyone have a suggestion to help me run my program in R?

Thank you very much,

Emilie Berthiaume
graduate student
Biology Department
Sherbrooke University
Sherbrooke, Quebec
CANADA

emilie.berthiaume@USherbrooke.ca
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