Hi Patrick, >> The default in glm is cont.treatment (for unordered factors) and that >> leads to compare each level to the first one. I would rather prefer to >> compare the 2nd to the 1st, the 3rd to the 2nd, the 4th to the 3rd, >> etc...
The functions ?C and ?contrasts allow you to set up your own contrast matrix. A function to carry out the type of comparisons you are interested in has been written by Venables & Ripley. See contr.sdif in package MASS. Regards, Mark. Patrick Giraudoux wrote: > > Dear listers, > > I would like to compare the levels of a factor with 8 age categories > (0,10] (10,20] (20,30] (30,40] (40,50] (50,60] (60,70] (70,90] (however, > the factor has not been ordered yet). The default in glm is > cont.treatment (for unordered factors) and that leads to compare each > level to the first one. I would rather prefer to compare the 2nd to the > 1st, the 3rd to the 2nd, the 4th to the 3rd, etc... My understanding is > that cont.poly may make the trick, eg specified like this: > > mod3<-glm(AE~agecat, family=binomial,data=qinghai2, > contrasts=list(agecat="contr.poly")) > > but I am not sure to be right. > > Would be grateful if a true statistician can confirm or fire me... and > before definitive fire tell me how to manage with this... > > ______________________________________________ > 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. > > -- View this message in context: http://www.nabble.com/Comparison-of-age-categories-using-contrasts-tp22031426p22032444.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.
