Dear Ralf, Thanks for the additional suggestions -- I'll take a look at them as well.
John -------------------------------- John Fox, Professor Department of Sociology McMaster University Hamilton, Ontario Canada L8S 4M4 905-525-9140x23604 http://socserv.mcmaster.ca/jfox -------------------------------- > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Ralf Goertz > Sent: Wednesday, October 17, 2007 6:00 AM > To: John Fox > Cc: r-help@r-project.org > Subject: Re: [R]library(car): Anova and repeated measures > without between subjects factors > > John Fox, Dienstag, 16. Oktober 2007: > > Dear Ralf, > > > > Unfortunately, Anova.mlm(), and indeed Anova() more > generally, won't > > handle a model with only a constant. As you point out, this isn't > > reasonable for repeated-measures ANOVA, where it should be > possible to > > have only within-subjects factors. When I have a chance, > I'll see what > > I can do to fix the problem -- my guess is that it shouldn't be too > > hard. > > > > Thanks for pointing out this limitation in Anova.mlm() > > Dear John, > > I am looking forward to your having a chance. There is one > thing that I would like to request, though. > Greenhouse-Geisser and Huyn-Feldt eps corrections have > already been implemented but how about Mauchly's sphericity > test? I know this can be done with mauchly.test() but it > would be nice to have it in the summary of Anova(). > > However, there is one more thing. Look at the following data > > > c1<-c(-6.0,-10.3,-2.9,-8.3,-10.0,5.3,-7.7,-0.8,9.1,-6.2) > > mat<-matrix(c(c1,c1),10,2) > > mat > [,1] [,2] > [1,] -6.0 -6.0 > [2,] -10.3 -10.3 > [3,] -2.9 -2.9 > [4,] -8.3 -8.3 > [5,] -10.0 -10.0 > [6,] 5.3 5.3 > [7,] -7.7 -7.7 > [8,] -0.8 -0.8 > [9,] 9.1 9.1 > [10,] -6.2 -6.2 > > > bf<-ordered(rep(1:2,5)) > > bf > [1] 1 2 1 2 1 2 1 2 1 2 > Levels: 1 < 2 > > Since the two columns of mat are equal: > > > t.test(mat[,1],mat[,2],paired=T) > > Paired t-test > > data: mat[, 1] and mat[, 2] > t = NaN, df = 9, p-value = NA > alternative hypothesis: true difference in means is not equal to 0 > 95 percent confidence interval: > NaN NaN > sample estimates: > mean of the differences > 0 > > I would assume to either get a warning or a F-value of 0 for > the repeated factor zeit but actually: > > > Anova(lm(mat~bf),idata=data.frame(zeit=ordered(1:2)),idesign=~zeit) > > Type II Repeated Measures MANOVA Tests: Pillai test statistic > Df test stat approx F num Df den Df Pr(>F) > bf 1 0.0020 0.0163 1 8 0.9016 > zeit 1 0.2924 3.3059 1 8 0.1065 > bf:zeit 1 0.0028 0.0221 1 8 0.8854 > > whereas > > > anova.mlm(lm(mat~bf),X=~1,idata=data.frame(zeit=ordered(1:2))) > > Error in anova.mlm(...) : > residuals have rank 1 < 2 > > This is quite dangerous. In a real data situation I > accidentally used the same column twice and I got a > significant effect for the factor zeit! I hope it wouldn't be > too hard to fix this. too. > > Ralf > > ______________________________________________ > 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. > ______________________________________________ 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.
