slight correction...poor addition skills....
a contrast for a single regressor of G1R1 for example might be:
ones(1,14)/17 zeros(1,31) ones(1,3)/17 1 0 1 0 1 0 0 0
By that logic, a contrast between G1R1-G1R2 would be:
ones(1,14)/17 zeros(1,31) ones(1,3)/17 1 0 1 -1 1 -1 0 0
...but the problem persists....
On Thu, 14 Aug 2008 06:28:54 +0100, Amit Etkin <[log in to unmask]> wrote:
>Hi all,
>
>I've been playing with ANOVAs, and currently have one set up in which there
>is a two-level within subject factor ("region") and a two level across
>subjects factor ("group") and subjects themselves are modeled as factors
>(see the attached design matrix...ignore the funniness of the matrix at the
>bottom...that was the addition of 3 new subjects to group 1). In total there
>are 17 in group 1 and 31 in group 2.
>
>What I am interested in doing is to do a valid conjunction analysis (using
>Tom Nichols' method) in SPM5. To do so, I have to be able to specify two
>valid contrasts, select them both, and this will bring up the conjunction
>option. I'd like to evaluate the conjunction of regions (R1-R2) for group 1
>with the same contrast for group 2 (rather than doing an overall effect of
>region analysis within the ANOVA, since overlap is important to assess and
>the sample sizes are quite different).
>
>The problem I'm having, however, is that I can't create valid contrasts for
>R1-R2 separately for each region. I've been going off of the contrast
>specification article that Jan Glascher and Darren Gittleman wrote,
>according to which a contrast for a single regressor of G1R1 for example
>might be:
>
>ones(1,14)/14 zeros(1,31) ones(1,3)/14 1 0 1 0 1 0 0 0
>
>By that logic, a contrast between G1R1-G1R2 would be:
>
>ones(1,14)/14 zeros(1,31) ones(1,3)/14 1 0 1 -1 1 -1 0 0
>
>Neither of these gives valid contrasts, in part because neither sum to 0.
>I'm not sure how to get around this problem and would appreciate any advice!
>
>thanks,
>Amit
>
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