Hope I am not too late joining this thread. I believe the difference between R and SPSS is because SPSS adjusts the Type III SS by the harmonic mean of the unbalanced cell sizes. This calculation is discussed in Maxwell and Delaney (1990, pp. 271-297).
In short, the best explanation I can offer (details see below) is that SPSS and R produces the same output if you tell SPSS to do SSTYPE(1) or SSTYPE(2) instead of the default SSTYPE(3). As discussed in Maxwell and Delaney, the calculations of SS1 and SS2 do not involve the harmonic mean. Maxwell and Delaney discussed the pros and cons of each type of Sums of Squares. Apparently SPSS thinks that the harmonic mean SS3 is the *right* analysis. Like people who responded before me, I'd also suggest the use of lme() in unbalanced designs. Yuelin. ---- details ------- I used the Hays.df data: http://www.psych.upenn.edu/~baron/rpsych/rpsych.html And I added one between-subject variable: Hays.df$grpuneven <- c(1,1,1,1,1,1,1,1,2,2,2,2) # n=8 in grp 1; 4 in grp 2 I ran aov(rt ~ grpuneven*color*shape + Error(subj/shape+color), data=Hays.df) which gives you the same output as SSTYPE(1) and SSTYPE(2) using this syntax in SPSS. GLM Sh1Col1 Sh2Col1 Sh1Col2 Sh2Col2 BY grpuneven /WSFACTOR = color 2 Polynomial shape 2 Polynomial /METHOD = SSTYPE(2) /CRITERIA = ALPHA(.05) /WSDESIGN = color shape color*shape /DESIGN = grpuneven . -- Gilbert G wrote --|Sun (Nov/04/2007)[04:34]|--: 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. [... snip ...] 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? ===================================================================== Please note that this e-mail and any files transmitted with it may be privileged, confidential, and protected from disclosure under applicable law. If the reader of this message is not the intended recipient, or an employee or agent responsible for delivering this message to the intended recipient, you are hereby notified that any reading, dissemination, distribution, copying, or other use of this communication or any of its attachments is strictly prohibited. If you have received this communication in error, please notify the sender immediately by replying to this message and deleting this message, any attachments, and all copies and backups from your computer. ______________________________________________ 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.
