Hi Jeff,
why don't you go with the 'Full Factorial' option? In that case, SPM5
will actually specify the interaction contrasts for, you including the
3-way interaction you are interested in (and you can of course create
more specific contrasts yourself). Here you will have to specify how
many factors and levels you have, and then just select the con images
that correspond to a given cell of your 2x2x2 design.
Also, yes, the within-subjects factor is not independent, while the
between-subjects factors are. It is my understanding though that you
shouldn't assume equal variances for either.
Good luck,
Tobias.
On 3/22/07, Jeff Browndyke, Ph.D. <[log in to unmask]> wrote:
>
>
>
> Wise listmates,
>
>
>
> After beating my head against the wall for awhile and read-rereading the FIL
> manual, I'm at an impasse in how to set up a mixed design in SPM5 with a
> within-subject factor "feedback" (2 levels) and two between-subject factors
> "group" (2 levels) and "impairment" (2 levels). Additionally, it's my
> understanding that SPM5 is only capable of visualizing 2-way interactions,
> but there may be a way to set up a contrast to see the 3-way interaction of
> group x impairment x feedback? How do I specify the 3-way interaction? Is
> it just a difference of interactions below (i.e., [3 4] [3 2])?
>
>
>
> Here's what I can glean so far:
>
> 1.) Flexible factorial design
>
> 2.) Factors: subject (reserved word – not certain if this is a place
> marker for one of the two between-subject factors or separate factor
> altogether), feedback, group, impairment
>
> (I'm I correct in specifying that the within factor is non-independent/equal
> variance, while the two between factors are independent/nonequal variance?)
>
> 3.) "Subjects" -> "Scans" -> "Specify Files" (2 .con images for each
> subject referring to the two levels of the "feedback" within-subject factor)
>
> 4.) "Conditions" -> completely stuck here! I've found examples for
> single within- x between-factor, but nothing specifying single within- x two
> between-factors.
>
> 5.) "Main effects and interactions" ->
>
> Main Effect 1 (feedback): 2
>
> Main Effect 2 (group): 3
>
> Main Effect 3 (impairment): 4
>
> Main Effect 4 (subject/constant): 1
>
> Interaction 1 (group*impairment): 3 4
>
> Interaction 2 (group*feedback) 3 2
>
> Interaction 3 (impairment*feedback) 4 2
>
>
>
> Am I on the right track? Any assistance or pointers toward walkthroughs or
> data examples pertinent to my needs would be most appreciated.
>
>
>
> Cheers,
>
> Jeff
--
Tobias Egner, Ph.D.
Cognitive Neurology and Alzheimer's Disease Center
Feinberg School of Medicine
Northwestern University
320 East Superior, Searle 11
Chicago, IL 60611
Ph: (+1) 312 503 1749
Fax: (+1) 312 908 8789
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