Playing around with this some more, it looks like it may purely be due to the way that R handles unbalanced data. I will investigate lme for this.
Best, Gabe On Wed, Apr 8, 2009 at 3:24 PM, Gabriel Murray <p.edi...@gmail.com> wrote: > Here is some toy data to give an example. Imagine someone is test-riding > several bicycles to decide which to buy, and measures their average speed > during each test-ride. They want to assess the main effects and interaction > of brand and material on speed. > > Speed Size Brand Material > 20 small giant steel > 25.1 medium giant steel > 25.2 medium trek aluminum > 26 small cannondale carbon > 19.9 large giant aluminum > 21 medium trek carbon > 30 medium cannondale carbon > > This is the output I get: > > > fit = aov(Speed~Brand*Material, data=myData) > > summary(fit) > Df Sum Sq Mean Sq F value Pr(>F) > Brand 2 49.862 24.931 2.3738 0.2964 > Material 2 13.502 6.751 0.6428 0.6087 > Residuals 2 21.005 10.503 > > > I suppose I am missing something very obvious here as to why the > interaction is not reported, but I don't see what it is. > Cheers, > > Gabe > > > > On Wed, Apr 8, 2009 at 1:34 PM, Patrick Connolly < > p_conno...@slingshot.co.nz> wrote: > >> On Wed, 08-Apr-2009 at 12:59PM -0700, Gabriel Murray wrote: >> >> |> I've noticed with certain datasets that when I try to do an anova and >> test >> |> for main effects and interaction for two explanatory variables, >> sometimes >> |> the main effect results are given but not the interaction results. For >> |> example, >> |> >> |> ex1 = aov(Score ~ var1*var2, data=myData) >> |> summary(ex1) >> >> Could it be that there are no degrees of freedom left? >> >> That's about my best guess without enough information. >> >> >> |> ______________________________________________ >> |> 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. >> >> >> Nothing you sent is reproducible. >> >> >> -- >> ~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~. >> ___ Patrick Connolly >> {~._.~} Great minds discuss ideas >> _( Y )_ Average minds discuss events >> (:_~*~_:) Small minds discuss people >> (_)-(_) ..... Eleanor Roosevelt >> >> ~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~. >> > > [[alternative HTML version deleted]] ______________________________________________ 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.
