Hi,
I'd like to look at Effects of Interest using SPM8 but I am having trouble inputting the contrast matrix for the F-contrasts.
The matrices I have tried give me highly significant regions across the entire brain: i.e. F-values of at least 1000 in every voxel (within the mask).
I'd like to run an equivalent of one-way ANOVA on PET images from 3 groups of patients.
I've created a factorial design - design matrix is 3 columns (n1=14, n2=10, n3=12)
I've tried F-contrast matrices 2 different ways both giving the extremely high F values
Using contrast weights matrix = [1 0 0; 0 1 0; 0 0 1]
OR using the "columns for reduced design" = 0 => [14 0 0; 0 10 0; 0 0 12]
I have tried the same using just 2 groups ("Two Sample T-Test"), assuming this is the equivalent of a 2-sided t-test, but the same extreme values appear.
Have I entered something incorrectly or made the wrong assumptions?
Cheers
Joel
PS - running SPM8 on Matlab R2009a on Windows XP; for simplicity I have assumed equal variance and independence between the groups; I used global scaling to mean (proportional). Linear T-contrasts show only specific regional differences.
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