Hi Steve,
thank you for the reasurrance that my designs are ok.
However, I am still confused about the contrast masking. As I mentioned
previously I have read the manual and also other postings on the issue, but
remain confused and was hoping you could clarify.
For example I want to look at Pre (Left > Right) Vs Post (Left > Right). I
therefore want to know where the Pre group had greater activation than the
post group when looking at Left vs Right.
so if I assume that if I have the contrasts
C1 = Pre (left>right)
C2 = Post (left>right)
C3 = Pre>Post
C4 = Post>pre
would I contrast C3 with C1 AND C2? And then do the same for C4?
I am unsure as to when I contrast with one or both masks.
And presumably if I use the Z>0 I am only looking at positive activation?
Is this correct?
Thanks in advance for any clarification and I again apologise for my basic
understanding of analysis.
Rebecca
On Wed, 11 Mar 2009 06:37:15 +0000, Steve Smith
<[log in to unmask]> wrote:
>Hi,
>
>You can certainly run any contrasts between these groups with FEAT,
>but I'm still not sure in what way it makes sense here to use the
>controls, given that you didn't also give them the treatment. You can
>run the following contrasts that make some sense:
>
>controls-patientsPRE (unpaired t-test model)
>controls-patientsPOST (unpaired t-test model)
>patientsPOST-PRE (paired t-test)
>
>See the FEAT manual for example models.
>Hopefully this will give you the results you need?
>
>Cheers.
>
>
>
>On 10 Mar 2009, at 08:30, Rebecca Leigh wrote:
>
>> Hi Steve,
>> sorry I should have been clearer about my groups.
>>
>> My controls are healthy volunteers, my training group consist of
>> patients.
>> I therefore want to examine how patients differ to healthy controls
>> prior to
>> training and how they differ after training.
>> Do my FEAT analysis seem reasonable if this is what I want to examine?
>>
>
>
>--------------------------------------------------------------------------
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>Stephen M. Smith, Professor of Biomedical Engineering
>Associate Director, Oxford University FMRIB Centre
>
>FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
>+44 (0) 1865 222726 (fax 222717)
>[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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