The design matrix is the problem. Both condition 2 and the scanner
covariate are identical and that is creating the problem. I don't
think its feasible to seperate the differences between conditions and
differences between conditions given the experiment described.
On Wed, Nov 26, 2008 at 7:40 PM, Christa Watson <[log in to unmask]> wrote:
> Dear SPM list,
> I am trying to enter contrasts for my paired t analysis but cannot seem to
> enter the correct contrasts. For my experiment, I have 9 subjects who were
> scanned on both a GE and Siemens scanner. So, the conditions are GE (1) and
> Siemens (2). We are also trying to determine if using scanner as a
> covariate will properly alleviate any differences we may see. I entered my
> paired scans as Pair 1: 1-GE,2-Siemens; Pair 2: 1-GE, 2-Siemens, etc. The
> contrast I want to run is condition 1 - condition 2 (GE-SN).
> So far I have tried the following without success:
> t-test
> repmat(0,1,9) 0 1 -1
> repmat (0,1,10) 1 -1
> 0 0 0 0 0 0 0 0 0 1 -1
>
> F test
> reduce columns 1:10
>
> Please advise me on how to enter the contrast for an analysis of GE scans -
> Siemens scans (Condition 1 - Condition 2).
> I have a attached a jpeg of the design matrix for clarification.
> Thank you very much, in advance, for your help,
> Christa
>
> Christa Watson
> Center for Interdisciplinary Brain Sciences Research
> Stanford University
> Dept. of Psychiatry and Behavioral Sciences
> 401 Quarry Road, MC 5795
> Stanford, CA 94305-5795
> phone: (650) 736-0732
> email: [log in to unmask]
> *************************************************************
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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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