This is failing because it is a saturated model and the contrast package tries to do a t-test (instead of a z test). I can add code to do this, but it will take a few days.
Max On Fri, Oct 28, 2011 at 2:16 PM, John Sorkin <jsor...@grecc.umaryland.edu> wrote: > Forgive my resending this post. To data I have received only one response > (thank you Bert Gunter), and I still do not have an answer to my question. > Respectfully, > John > > > Windows XP > R 2.12.1 > contrast package. > > > I am trying to understand how to create contrasts for a model that contatains > an interaction. I can get contrasts to work for a model without interaction, > but not after adding the interaction. Please see code below. The last two > contrast statements show the problem. I would appreciate someone letting me > know what is wrong with the syntax of my contrast statements. > Thank you, > John > > > library(contrast) > > # Create 2x2 contingency table. > counts=c(50,50,30,70) > row <- gl(2,2,4) > column <- gl(2,1,4) > mydata <- data.frame(row,column,counts) > print(mydata) > > # Show levels of 2x2 table > levels(mydata$row) > levels(mydata$column) > > > # Models, no interaction, and interaction > fitglm0 <- glm(counts ~ row + column, family=poisson(link="log")) > fitglm <- glm(counts ~ row + column + row*column, family=poisson(link="log")) > > # Contrasts for model without interaction works fine! > anova(fitglm0) > summary(fitglm0) > con0<-contrast(fitglm0,list(row="1",column="1")) > print(con0,X=TRUE) > > # Contrast for model with interaction does not work. > anova(fitglm) > summary(fitglm) > con<-contrast(fitglm,list(row="1",column="1") > print(con,X=TRUE) > > # Nor does this work. > con<-contrast(fitglm,list(row="1",column="1",row:column=c("0","0"))) > print(con,X=TRUE) > > > > > John David Sorkin M.D., Ph.D. > Chief, Biostatistics and Informatics > University of Maryland School of Medicine Division of Gerontology > Baltimore VA Medical Center > 10 North Greene Street > GRECC (BT/18/GR) > Baltimore, MD 21201-1524 > (Phone) 410-605-7119 > (Fax) 410-605-7913 (Please call phone number above prior to faxing) > > Confidentiality Statement: > This email message, including any attachments, is for ...{{dropped:16}} ______________________________________________ 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.