I am having problems with defining the error terms for a two way repeated measures ANOVA in R. My data consists of wood density estimates for three radial positions (inner, middle, and outer) along a core extracted from a tree. There are a total of 20 tree species, 6 individuals of each species, and two cores from each tree.

To test the effect of radial position on wood density, I use the following two way ANOVA model with an error term that accounts for variability across individuals:

radpos.aov <- aov(WD ~ Species*Radialposition + Error(Individual), data=Radpos)

However, I am not sure if my specification of the error term is adequate. Am I also supposed to account for the variability within a core? To me this variability is the same as that due to radial position which is the main factor I am interested in.

Although I have devoted some time to reading about specifying the error term in Repeated measures ANOVA, I still have problems with practically specifying the error term. I will appreciate some help with this.


1 Answer 1


It would be

 radpos.aov <- aov(WD ~ Species*Radialposition + Error(Individual/(Radialposition)), data=Radpos)
 summary(radpos.aov, type=3)

That accounts for the within subject error of Radialposition. If you have other within-subject factors, throw them in (in an interaction) with Radialposition in the Error denominator, like + Error(Individual/(Radialpostion*wiFactorA)). That's my understanding of it. That matches up with SPSS's repeated measures GLM if you have no missing data.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.