Prof Brian Ripley used his keyboard to write : > On Mon, 26 Nov 2007, Max wrote: > >> Prof Brian Ripley explained : >>> On Mon, 26 Nov 2007, Max wrote: >>> >>>> Hi everyone, I'm trying to understand some R output here for ordinal >>>> regression. I have some integer data called "A" split up into 3 ordinal >>>> categories, top, middle and bottom, T, M and B respectively. >>>> >>>> I have to explain this output to people who have a very poor idea about >>>> statistics and just need to make sure I know what I'm talking about >>>> first. >>>> >>>> Here's the output: >>>> >>>> Call: >>>> polr(formula = Factor ~ A, data = a, Hess = TRUE, method = "logistic") >>>> >>>> Coefficients: >>>> Value Std. Error t value >>>> A -0.1259028 0.04758539 -2.645829 >>>> >>>> Intercepts: >>>> Value Std. Error t value >>>> B|M -2.5872 0.5596 -4.6232 >>>> M|T 0.3044 0.4864 0.6258 >>>> >>>> Residual Deviance: 204.8798 >>>> AIC: 210.8798 >>>> >>>> I really am not sure what the intercepts mean at all. However, my >>>> understanding of the coefficient of A is that as the category >>>> increases, A decreases? If I have an A value of 10, how to I figure out >>>> the estimated probability that this score is in one of the three >>>> categories? >>> >>> Use predict(): see the book polr supports for examples (and the theory). >> >> I appreciate the reply, but have difficulty understanding what you mean >> by "the book polr supports"? :-? >> >> The manuals in R don't reference the polr() command, nor do they write >> about ordinal regression in R. (from what I can tell) The documentation >> of the polr() doesn't explain the output or the theory... I've done web > > It _does_ describe both the theory and the use of predict(), on pages > 204-5.
Is this in your textbook? I found the explanation for predict on page 1194 of the R reference manual pdf from the help menu in the GUI. Unfortunately I do not have the MASS textbook itself, and have to rely on whatever I can find about polr() from web. > >> searches on polr() and the MASS library and have found little of direct >> help to my question. > > polr is in the MASS package (although you failed to mention that, or give > credit). From library(help=MASS) > > BundleDescription: Functions and datasets to support Venables and > Ripley, 'Modern Applied Statistics with S' (4th > edition). > and from ?polr: > > References: > > Agresti, A. (2002) _Categorical Data._ Second edition. Wiley. > > Venables, W. N. and Ripley, B. D. (2002) _Modern Applied > Statistics with S._ Fourth edition. Springer. Thanks guys for the help. I'm still very new to R and didn't even know the library(help=MASS) command, I was googling things before... And I apologize for not properly crediting you Prof. Ripley, I'm quite new to this newsgroup as well, no insult was intended, I just didn't know any better. I'll see about finding your book, I'm hopeful I can convince my employer to purchase me some R books. That or I'll spend my own money, as it seems a couple texts on R would be extremely useful. ______________________________________________ R-help@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.
