Dear Peter, Yes, you're absolutely right -- of course (though I didn't notice it!), the precedence of / and * in a formula is like division and multiplication in an arithmetic expression. With this correction, the SSs and error SSs are properly matched by aov(), producing the same F-tests as Anova().
Thank you, John > -----Original Message----- > From: Peter Dalgaard [mailto:p.dalga...@biostat.ku.dk] > Sent: February-20-09 6:06 PM > To: John Fox > Cc: 'Tal Galili'; r-help@r-project.org > Subject: Re: [R] [package-car:Anova] extracting residuals from Anova for Type > II/III Repeated Measures ? > > John Fox wrote: > > Dear Tal, > > > > I didn't have time to look at all this yesterday. > > > > Since aov() doesn't do what I typically want to do, I guess I've not paid > > much attention to it recently. I can see, however, that you appear to have > > specified the error strata incorrectly, since (given your desire to compare > > to Anova) the within-block factors are nested within blocks. Something like > > > >> npk.aovE <- aov(value ~ N*P*K + Error(block/N*P*K), npk.long) > > > > should be closer to what you want, and in fact produces all of the sums of > > squares, but doesn't put all of the error terms together with the > > corresponding terms; thus, you get, e.g., the test for N but not for P and > > K, even though the SSs and error SSs for the latter are in the table. By > > permuting N, P, and K, you can get the other F tests. I suspect that this > > has to do with the sequential approach taken by aov() but someone else more > > familiar with how it works will have to fill in the details. I wonder, > > though, whether you've read the sections in Statistical Models in S and > MASS > > referenced in the help file for aov. > > Does it not help if you use Error(block/(N*P*K))? I suspect you're being > bitten by operator precedence, of the same making as the fact that 1/2*2 > is 1, not 0.25. > > -pd > > -- > O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B > c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K > (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 > ~~~~~~~~~~ - (p.dalga...@biostat.ku.dk) FAX: (+45) 35327907 ______________________________________________ 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.
