The designs are different and have different assumptions about the
data. The following website has a great explanation of your two
models:
http://mumford.fmripower.org/mean_centering/
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Mon, Jul 23, 2012 at 5:52 AM, Giulia Preti <[log in to unmask]> wrote:
> Hi there,
>
> I'm running an fMRI analysis and I'm trying to set up a design matrix to perform an ANOVA with 3 groups of subjects (controls, two groups of patients) and one covariate (task performance).
>
> I set up the design matrix like in the example below:
>
>
> Group EV1 EV2 EV3 EV4
> 1 1 0 0 9,70
> 1 1 0 0 9,70
> 1 1 0 0 9,70
> 1 1 0 0 9,70
> 1 0 1 0 7,70
> 1 0 1 0 4,14
> 1 0 1 0 -12,52
> 1 0 0 1 -10,30
> 1 0 0 1 -20,86
> 1 0 0 1 -6,97
>
> CONTRASTS:
>
> 1 -1 0 0
> 1 0 -1 0
> 0 1 -1 0
> -1 1 0 0
> -1 0 1 0
> 0 -1 1 0
>
>
>
>
> Is this correct? Is it the same if I specify the value 1,2,3 for the column "Group" and split the performance column (EV4) in 2 different columns like below (demeaning for each column separately and deleting the column of the controls'performances, since it woul be all 0)?
>
>
> Group EV1 EV2 EV3 EV4 EV5
> 1 1 0 0 0 0
> 1 1 0 0 0 0
> 1 1 0 0 0 0
> 1 1 0 0 0 0
> 2 0 1 0 7,3 0
> 2 0 1 0 3,75 0
> 2 0 1 0 -12,9 0
> 3 0 0 1 0 2.41
> 3 0 0 1 0 -8.15
> 3 0 0 1 0 5.74
>
>
>
> What is the difference between the two designs, and which is better?
>
>
> Thank you in advance for your help.
>
>
> Giulia
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