> I wanted to do contrasts for 3 groups in which i want to look
> at gross differences between the 3 groups simultaneously. I
> specified the F-contrast in one-way ANOVA test as such:
> -1 0 1 (Group1 < Group3)
> -1 1 0 (Group1 < Group2)
> 0 -1 1 (Group2 < Group3)
>
> I have one scan/one condition per patient. I was hoping this would
> show me hypo-active areas in Group1. When I change the contrast to
> 1 0 -1
> 1 -1 0
> 0 1 -1
>
> I get the same map. Should not the second one show the hyperactive areas? Thank you so much,
>
No.
F-contrasts look for two-sided effects.
With both contrasts you are testing
(Group1 not = Group 3) or (Group 1 not = Group 2) or (Group2 not = Group 3)
Best,
Will.
--
William D. Penny
Wellcome Department of Imaging Neuroscience
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7475
FAX: 020 7813 1420
Email: [log in to unmask]
URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
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