I'm surprised there were no takers on this query; I thought it would be an easy answer, particularly where I provided example data set and code. Did my request run afoul of the list etiquette?
On Tue, Feb 10, 2009 at 5:12 PM, Mike Lawrence <m...@thatmike.com> wrote: > Hi all, > > I have data from an experiment with 3 independent variables, 2 are > within and 1 is between. In addition to the dependent variable, I have > a covariate that is a single measure per subject. Below I provide an > example generated data set and my approach to implementing the ANCOVA. > However the output confuses me; why does the covariate only appear in > the first strata? Presumably it should appear in every strata in which > there can be between-Ss effects or interactions with between-Ss > effects, no? > > #generate data > set.seed(1) > a=rbind( > expand.grid( > id=1:20 > ,iv1 = 1:2 > ,iv2 = 1:2 > ) > ) > a$group = factor(a$id<11) > a$dv = rnorm(length(a[,1])) > a$covariate = NA > for(i in unique(a$id)){ > a$covariate[a$id==i]= rnorm(1) > } > > #make sure id, iv1, and iv2 are factorized > a$id=factor(a$id) > a$iv1=factor(a$iv1) > a$iv2=factor(a$iv2) > > #run ANCOVA > covariate_aov = aov(dv~covariate+group*iv1*iv2+Error(id/(iv1*iv2)),data=a) > summary(covariate_aov) > > > -- > Mike Lawrence > Graduate Student > Department of Psychology > Dalhousie University > www.thatmike.com > > Looking to arrange a meeting? Check my public calendar: > http://www.thatmike.com/mikes-public-calendar > > ~ Certainty is folly... I think. ~ > -- Mike Lawrence Graduate Student Department of Psychology Dalhousie University www.thatmike.com Looking to arrange a meeting? Check my public calendar: http://www.thatmike.com/mikes-public-calendar ~ Certainty is folly... I think. ~ ______________________________________________ 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.