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Hi Josh,

You want to use either a flexible factorial model in SPM (with a subject factor) or one of the GLM_Flex models (I'm not sure which version is best, you can ask that mailing list for the current model to use). Alternatively, if you are not interested in the 3-ways interaction, that is unlikely to significant with 3 subjects, you could collapse some one the factors and use the SPM flexible factor out of the box with the subject factor.

I believe there is a way around SPM's limit of 3 factors and that you can use 3 factors plus the subject factor. There has been some recent posts around this issue.

Best Regards, 
Donald McLaren, PhD


On Mon, Aug 27, 2018 at 7:20 PM, Joshua Stivers <[log in to unmask]> wrote:
Hello all,
I've done my best to research this myself, but I was hoping for confirmation/advice.

I'm attempting to implement a 2 (Stimulus Category) x 2 (Task) x 2 (Performance: Success/Failure) Repeated Measures ANOVA in SPM. Consulting this mailing list, I'm worried that my model, specified as a full factorial design, is inappropriate for this analysis. It has been suggested several times that flexible factorial is necessary for repeated measures designs, as full factorial underestimates inter-subject variability. 

However, most of the designs people have been asking about involve at least one between-subject component (i.e. treatment group vs. control). My dataset consist of 16 subjects, and all of them experience all levels of the 3 factors. If it is necessary to include subjects as a factor, is GLM_flex (in particular, GLM_flex2) still considered the ideal approach for ANOVAs with more than 3 factors? I undertand 4-factor analysis is unlikely to be implemented in SPM.

Best,
Josh