# Why aov() with Error() gives three strata?

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## Why aov() with Error() gives three strata?

 Dear list users, I am trying to learn Repeated measures ANOVA using the aov() interface, but I'm struggling to understand its output. According to tutorials on the web, formula for a repeated measures design is: aov(Y ~ IV+ Error(SUBJECT/IV) ) This formula does work but it returns three strata (Error:SUBJECT, Error: SUBJECT:IV, Error: Within), when I would expect two strata (Within and Between subjects). I've seems some tutorials  show the exactly same setup, but returning only the two first strata. Is it possible to have two or three strata depending on the data? If there is always three strata, how this would fit the interpretation of between vs within effects? Below a reproducible example that gives three strata: data(beavers) data=data.frame(id = rep(c("beaver1","beaver2"),c(nrow(beaver1),nrow(beaver2))),rbind(beaver1,beaver2)) data\$activ=factor(data\$activ) #balance dataset to have 6 samples for every combination of beaver and activity. balanced = split(data,interaction(data\$id,data\$activ)) sizes = sapply(balanced,nrow) selected = lapply(sizes,sample.int,6) balanced = mapply(function(x,y) {x[y,]}, balanced,selected,SIMPLIFY=F) balanced = do.call(rbind,balanced) aov(temp~activ+Error(id/activ),data=balanced) Thanks, Jorge         [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
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## Re: Why aov() with Error() gives three strata?

 Jorge: FYI, *generally speaking,* queries that are mostly statistical in nature, such as yours, are off topic here -- this list is about R programming help, not statistical help. Having said that, you still may get a useful response here -- the r-help/statistics intersection *is* nonempty. However, if not, 2.5 suggestions: 1. Try posting to r-sig-mixed-models instead. Repeated measures are a type of mixed/multilevel model and you may receive some useful suggestions there, including alternative R approaches to fitting such model (e.g. using lme() or lmer() ). 2. Alternatively, try posting to a statistics site like stats.stackexchange.com. 2.5. Or, if you can, the best idea might be to sit down with a local statistics expert. Cheers, Bert Bert Gunter "The trouble with having an open mind is that people keep coming along and sticking things into it." -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) On Thu, Dec 28, 2017 at 7:52 AM, Jorge Fernando Saraiva de Menezes <[hidden email]> wrote: > Dear list users, > > I am trying to learn Repeated measures ANOVA using the aov() interface, but > I'm struggling to understand its output. > > According to tutorials on the web, formula for a repeated measures design > is: > > aov(Y ~ IV+ Error(SUBJECT/IV) ) > > This formula does work but it returns three strata (Error:SUBJECT, Error: > SUBJECT:IV, Error: Within), when I would expect two strata (Within and > Between subjects). I've seems some tutorials  show the exactly same setup, > but returning only the two first strata. > > Is it possible to have two or three strata depending on the data? > If there is always three strata, how this would fit the interpretation of > between vs within effects? > > Below a reproducible example that gives three strata: > > data(beavers) > data=data.frame(id = > rep(c("beaver1","beaver2"),c(nrow(beaver1),nrow(beaver2))),rbind(beaver1,beaver2)) > data\$activ=factor(data\$activ) > #balance dataset to have 6 samples for every combination of beaver and > activity. > balanced = split(data,interaction(data\$id,data\$activ)) > sizes = sapply(balanced,nrow) > selected = lapply(sizes,sample.int,6) > balanced = mapply(function(x,y) {x[y,]}, balanced,selected,SIMPLIFY=F) > balanced = do.call(rbind,balanced) > aov(temp~activ+Error(id/activ),data=balanced) > > Thanks, > Jorge > >         [[alternative HTML version deleted]] > > ______________________________________________ > [hidden email] mailing list -- To UNSUBSCRIBE and more, see > 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. ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
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