Dear All,
I have a longitudinal study design (ANOVA with repeated measures and two factors: factor group and factor condition with two levels each). According to the SPM8 manual, I generated a design matrix without problems.
Then I formed contrasts following the manual by Gläscher and Gitelman (http://www.sbirc.ed.ac.uk/cyril/download/Contrast_Weighting_Glascher_Gitelman_2008.pdf) in the following way:
1. I set the following variables in matlab:
“nc” for number of conditions, “ng” for number of groups,
“MEc” for main effect of condition >>MEc = [1:nc] –mean(1:nc),
“Meg” for main effect of group>>MEg = [1 -1]
2. The contrast template for main effect of group in the manual is defined as follows:
“MEg zeros(1,nc) ones (1, nc) /nc –ones (1,nc) /nc”
>> So for my design it would be: “ 1 -1 0 0 0.5 0.5 -0.5 -0.5”
3. The contrast template for main effect of condition in the manual is defined as follows:
“zeros(1,ng) MEc MEc*[n1/(n)] MEc*[n2/(n)]”
>> So for my design it would be: “0 0 0.5 -0.5 0.25 -0.25 0.25 -0.25”
Now I`m wondering about the 0.5 for condition. I would assume it should be 1 -1 ?
4. The contrast template for group/condition interaction in the manual is defined as follows: “0 0 0 0 MEc –Mec”
>> So for my design it would be:”0 0 0 0 0.5 -0.5 -0.5 0.5”
Could you tell me whether my contrasts are correctly specified?
Many thanks, Elisabeth
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