From: Dan Frankowski <dfrankow_at_gmail.com>

Date: Tue, 01 Mar 2011 15:29:46 -0600

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 01 Mar 2011 - 22:20:53 GMT

Date: Tue, 01 Mar 2011 15:29:46 -0600

Also posted as

http://stats.stackexchange.com/questions/7720/how-to-understand-output-from-rs-polr-function-ordered-logistic-regression
.

Also, I read section 7.3 of "Modern Applied Statistics with S" by Venables and Ripley (who wrote polr?), and I can still not answer many of these questions.

On Tue, Mar 1, 2011 at 3:25 PM, Dan Frankowski <dfrankow_at_gmail.com> wrote:

> I am new to R, ordered logistic regression, and polr.

*>
**> The "Examples" section at the bottom of the help page for polr<http://stat.ethz.ch/R-manual/R-patched/library/MASS/html/polr.html>(that fits a logistic or probit regression model to an ordered factor
**> response) shows
**>
**> options(contrasts = c("contr.treatment", "contr.poly"))
**>
**> house.plr <- polr(Sat ~ Infl + Type + Cont, weights = Freq, data = housing)
**>
**> pr <- profile(house.plr)
**>
**> plot(pr)
**> pairs(pr)
**>
**>
**> -
**>
**> What information does pr contain? The help page on profile<http://stat.ethz.ch/R-manual/R-patched/library/stats/html/profile.html>is generic, and gives no guidance for polr.
**> -
**>
**> What is plot(pr) showing? I see six graphs. Each has an X axis that is
**> numeric, although the label is an indicator variable (looks like an input
**> variable that is an indicator for an ordinal value). Then the Y axis is
**> "tau" which is completely unexplained.
**> -
**>
**> What is pairs(pr) showing? It looks like a plot for each pair of input
**> variables, but again I see no explanation of the X or Y axes.
**> -
**>
**> How can one understand if the model gave a good fit? summary(house.plr)shows Residual Deviance 3479.149 and AIC (Akaike Information Criterion?) of
**> 3495.149. Is that good? In the case those are only useful as relative
**> measures (i.e. to compare to another model fit), what is a good absolute
**> measure? Is the residual deviance approximately chi-squared distributed? Can
**> one use "% correctly predicted" on the original data or some
**> cross-validation? What is the easiest way to do that?
**> -
**>
**> How does one apply and interpret anova on this model? The docs say
**> "There are methods for the standard model-fitting functions, including
**> predict, summary, vcov, anova." However, running anova(house.plr)results in anova
**> is not implemented for a single "polr" object
**> -
**>
**> How does one interpret the t values for each coefficient? Unlike some
**> model fits, there are no P values here.
**>
**> I realize this is a lot of questions, but it makes sense to me to ask as
**> one bundle ("how do I use this thing?") rather than 7 different questions.
**> Any information appreciated.
**>
*

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