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Depends on your question, the contrast below is comparing group1 to the
average of groups 2-4.
An alternative is to ask the question:
Does group1 differ from group2 OR group1 differ from group3 OR group1 differ
from group4?

F= [1 -1 0 0; 1 0 -1 0; 1 0 0 -1]

Another alternative:
Do the groups differ from each other?
F=[1 -1 0 0; 0 1 -1 0; 0 0 1 -1]

On Thu, Mar 26, 2009 at 11:55 AM, Muhammad A Parvaz <[log in to unmask]>wrote:

> hi all,
>
> we are doing VBM using the VBM5 toolbox and we are doing an ANOVA with 4
> groups. i was wondering what is the correct way to specify the contrast
> when
> we want to compare one group against the other 3 groups. We are inclined to
> use the following weights for our contrast
>
> [-1 0.33 0.33 0.33]
>
> is this right? will decreasing the weight of each group to 0.33 change the
> signal and variance of that group in anyway?
>
> Is there a better way to specify this contrast?
>
> Thanks
> -Muhammad
>



-- 
Best Regards, Donald McLaren
=====================
D.G. McLaren
University of Wisconsin - Madison
Neuroscience Training Program
Office: (608) 265-9672
Lab: (608) 256-1901 ext 12914
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