Hi Mark,
Thanks for the response. As an extension of this problem (for which there were only 2 values for the regressor), how would one include a behavioral EV (i.e. depression score) into this design?
Thanks
Rachel
-----Original Message-----
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf Of Mark Jenkinson
Sent: Friday, August 12, 2011 8:10 AM
To: [log in to unmask]
Subject: Re: [FSL] dual regression within subjects
Dear Rachel,
Your last EV is redundant and should be removed.
You can form this EV by a combination of the last 19
subject-specific EVs. Hence it does not add anything
and could be causing problems.
All the best,
Mark
On 12 Aug 2011, at 12:57, Rachel Kozink wrote:
> Hi Steve,
>
> That's correct - it's the model for randomise. I've attached the model. It's not clear from this image, but there are 38 subjects, each run twice so for the "group" variable, I have 38 different groups. As you can see, the last EV models which scanner the data was collected on and needs to go across groups.
>
> Thanks
> Rachel
>
>
> From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf Of Stephen Smith
> Sent: Friday, August 12, 2011 2:33 AM
> To: [log in to unmask]
> Subject: Re: [FSL] dual regression within subjects
>
> Hi - I assume that you are talking about the model that you are feeding into randomise - probably best if you show us the model to comment on.
> Cheers, Steve.
>
>
> On 11 Aug 2011, at 14:24, Rachel Kozink wrote:
>
>
> I am setting up a dual regression for a within subjects design and would like to add in an additional covariate. The scans are pooled from two different scanners (although each subject had both of their scans on the same scanner). When looking at the ICA components, a couple components have a marked difference within the group of subjects that correlates to which scanner the data was collected on. So, we would like to include scanner as a nuisance covariate in our paired t-test. When setting up my design, I receive an error message that states: "Warning - design matrix uses different groups (for different variances), but these do not contain "separable" EVs for the different groups (it is necessary that, for each EV, only one of the groups has non-zero values). " It seems to allow me to continue, but I wanted to verify that the results that I will get will be valid.
>
> Thanks in advance,
> Rachel
>
>
>
> ---------------------------------------------------------------------------
> 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
> ---------------------------------------------------------------------------
>
>
>
> <paired_design.png>
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