Dear David, The short answer is that in a two-way ANOVA (or an analogous generalized linear model), the test for the interaction doesn't depend upon the contrast type, and is identical for "Type-II" and "Type-III" (and, indeed, "Type-I" -- i.e., sequential) tests. It's the main-effect tests that depend upon contrast type (for "Type-III" tests), and for which "Type-II" and "Type-III" tests differ. There's a longer answer in the book with which the car package is associated (and a longer one still in my Applied Regression text, as well as other places).
I hope this helps, John > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of David Jutier > Sent: Friday, May 07, 2004 6:20 AM > To: [EMAIL PROTECTED] > Subject: [R] contrasts in a type III anova > > Hello, > > I use a type III anova ("car" package) to analyse an > unbalanced data design. I have two factors and I would have > the effect of the interaction. I read that the result could > be strongly influenced by the contrasts. I am really not an > expert and I am not sure to understand indeed about what it is... > > Consequently, I failed to properly used the fit.contrast > function (gregmisc > package) because I don't understand what the fonction need in > the argument "coeff". > > The two factors are Y (Ya, Yb,..., Ye) and Auto (Auto1, > Auto2,...., Auto10) The responses are binomial (counts in the > matrice "mat") and gaussian (variable "tot"). I use the glm > procedure : > > glm1 <- glm (mat ~ y*auto, data, family=binomial) > glm2 <- glm (tot ~ y*auto, data, family=gaussian) > > Subsequently I use the Type III anova : > > Anova (glm1, type="III") > Anova (glm2, type="III") > > Using the contrast.treatment for both factors Y and Auto, R > gives coherent results, but I really not sure that this > contrasts are appropriate ! > > Thank's for your advices ! > David > > ______________________________________________ > [EMAIL PROTECTED] mailing list > https://www.stat.math.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
