From: liu abc <liu2074_at_yahoo.com>

Date: Tue 06 Sep 2005 - 00:42:39 EST

NOTE: Convergence criterion (GCONV=1E-8) satisfied. NOTE: There were 10 observations read from the data set WORK.ONE.

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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.html Received on Tue Sep 06 00:50:40 2005

Date: Tue 06 Sep 2005 - 00:42:39 EST

Hey, everyone,

I am using proportional odds model for ordinal responses in dose-response experiments. For some samll data, SAS can successfully provide estimators of the parameters, but the built-in function polr() in R fails. Would you like to tell me how to make some change so I can use polr() to obtain the estimators? Or anyone can give me a hint about the conditions for the existance of MLE in such a simple case? By the way, for the variable "resp" which must be ordered factor, how can I do it? Thanks a lot.

Guohui

The following is one example I used both in SAS and R.

in R:

library(MASS)

dose.resp = matrix( c(1,1,1,1,2,2,2,3,3,3, 2,2,3,3,4,4,5,4,5,5), ncol=2)
colnames(dose.resp)= c("resp", "dose")

dose.resp

#> dose.resp

*# resp dose
**# [1,] 1 2
**# [2,] 1 2
**# [3,] 1 3
**# [4,] 1 3
**# [5,] 2 4
**# [6,] 2 4
**# [7,] 2 5
**# [8,] 3 4
**# [9,] 3 5
**#[10,] 3 5
*

polr( factor(resp, ordered=T)~dose, data=dose.resp)

#Error in optim(start, fmin, gmin, method = "BFGS", hessian = Hess, ...) :

*# initial value in 'vmmin' is not finite
**#In addition: Warning message:
**#fitted probabilities numerically 0 or 1 occurred in:
**#glm.fit(X, y1, wt, family = binomial(), offset = offset)
*

in SAS

NOTE: PROC LOGISTIC is fitting the cumulative logit model. The probabilities

modeled are summed over the responses having the lower Ordered Values in the Response Profile table.

NOTE: Convergence criterion (GCONV=1E-8) satisfied. NOTE: There were 10 observations read from the data set WORK.ONE.

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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.html Received on Tue Sep 06 00:50:40 2005

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