I have used plor() to model a rather large 3-category dataset (~1500 data points, ~15 independent variables); from the resulting model (with a deviance slightly below the residual degrees of freedom), the training data are placed in only the two extreme categories. Though the result appears to indicate that there's only a relative 'narrow' bin for the medium group, [and when the dataset is re-organized into 2 categories, glm(family binomial(link = logit) ...) gives a model with a deviance reduced by about half from the 3-category polr() result], I am questioning if this (the 'narrow-bin') interpretation is too simplistic (or entirely incorrect), and wondering about the meaning of the absence of (fitted) data points in the medium group. Thanks in advance for any hints/pointers! -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
Prof Brian D Ripley
2002-Jun-21 06:37 UTC
[R] a question on statistics (rather than R-specific)
On Thu, 20 Jun 2002, Boryeu Mao wrote:> I have used plor() to model a rather large 3-category dataset (~1500 data > points, ~15 independent variables); from the resulting model (with a > deviance slightly below the residual degrees of freedom), the training data > are placed in only the two extreme categories. Though the result appears to > indicate that there's only a relative 'narrow' bin for the medium group, > [and when the dataset is re-organized into 2 categories, glm(family > binomial(link = logit) ...) gives a model with a deviance reduced by about > half from the 3-category polr() result], I am questioning if this (the > 'narrow-bin') interpretation is too simplistic (or entirely incorrect), and > wondering about the meaning of the absence of (fitted) data points in the > medium group. > > Thanks in advance for any hints/pointers!Probably the POLR model is inappropriate: try multinom for a fair comparison (you cannot compare likelihoods on grouped and ungrouped data). See the examples in MASS (the book) which is where polr() comes from. -- Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272860 (secr) Oxford OX1 3TG, UK Fax: +44 1865 272595 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
Thanks for the reply. Since the 3 categories are ordinal (the data are grouped into the categories from continuous variable), what would be the appropriate function for 2-category ordered data? (though I will try multinom() on the data.) -----Original Message----- From: Prof Brian D Ripley [mailto:ripley at stats.ox.ac.uk] Sent: Thursday, June 20, 2002 11:37 PM To: Boryeu Mao Cc: r-help at stat.math.ethz.ch Subject: Re: [R] a question on statistics (rather than R-specific) On Thu, 20 Jun 2002, Boryeu Mao wrote:> I have used plor() to model a rather large 3-category dataset (~1500 data > points, ~15 independent variables); from the resulting model (with a > deviance slightly below the residual degrees of freedom), the trainingdata> are placed in only the two extreme categories. Though the result appearsto> indicate that there's only a relative 'narrow' bin for the medium group, > [and when the dataset is re-organized into 2 categories, glm(family > binomial(link = logit) ...) gives a model with a deviance reduced by about > half from the 3-category polr() result], I am questioning if this (the > 'narrow-bin') interpretation is too simplistic (or entirely incorrect),and> wondering about the meaning of the absence of (fitted) data points in the > medium group. > > Thanks in advance for any hints/pointers!Probably the POLR model is inappropriate: try multinom for a fair comparison (you cannot compare likelihoods on grouped and ungrouped data). See the examples in MASS (the book) which is where polr() comes from. -- Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272860 (secr) Oxford OX1 3TG, UK Fax: +44 1865 272595 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._