Dear R people: I wish to switch from SPSS to R, but there is one particular type of ANOVA design that cannot be done in R. Or more likely, it can be done, but it is nowhere documented.
The problem is typical for psychologists: You have a repeated measures design with different groups of subjects. Now, this can be done with the aov command, but the number of subjects in both groups must be equal (i.e., balanced design). SPSS allows for unbalanced designs as well. If you are still with me, let me just give you an example of what R can and cannot do so far. Imagine I have a 2x2 within subjects design and I have 2 groups (e.g., group healthy and patients, which is stored in MyGroup). And imagine I measure reaction time RT in four conditions, say, in a color condition (red vs green) and in a shape condition (square vs circle). Now, in R you would have something like, as anybody who does balanced repeated measures anova's might know: aov( RT ~ color * shape * MyGroup + Error( Subjects/( color*shape) ) In spss you would have something like this (of course with the data organized slightly differently : GLM x1 x2 x3 x4 BY MyGroup /WSFACTOR = color 2 Polynomial shape 2 Polynomial /METHOD = SSTYPE(3) /CRITERIA = ALPHA(.05) /WSDESIGN = color shape color*shape /DESIGN = VAR00001 . Ok, the question is. If the group sizes are different (say 10 people in one group and 12 people in the other group) R is going to give the wrong answer. Of course that is not R's fault. BUT MY QUESTION IS: HOW TO GET THE UNBALANCED REPEATED MEASURES ANOVA RIGHT? Thanks for the answer! ______________________________________________ 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.
