As is my understanding of the FAQ: when the design matrix or number of
contrasts is large enough, it will be highly likely to be rank deficient?
But for the higher level analysis, I can carry on whatever combinations of
contrasts and the EVs won't add up to zero? If that's right, I think our
problem is solved.
Another question is whether the sum of all EVs has anything to do with my
If my control conditions are not optimally distributed, would that render my
design to be rank deficient?
Thanks a lot!
>From: "Christian F. Beckmann" <[log in to unmask]>
>Reply-To: FSL - FMRIB's Software Library <[log in to unmask]>
>To: [log in to unmask]
>Subject: Re: [FSL] design matrix rank deficiency
>Date: Mon, 11 Oct 2004 03:46:06 +0100
>this is covered in the FAQ, see
>http://www.fmrib.ox.ac.uk/fslfaq/#feat_rank for details. In order to
>give more specific advice we'd need to know details of your design -
>the feat directory should have design.mat and design.gif in it, maybe
>you want to post those?
>On 11 Oct 2004, at 01:56, Adam Gries wrote:
>>1) I've been trying to run a lower level analysis for a large number of
>>contrasts in different combinations and have received the following
>>At least one EV is (close to) a linear combination of the others. You
>>should probably alter your design. (Design matrix is rank deficient -
>>ratio of min:max eigenvalues in SVD of matrix is 0.000000e+00)
>>2) I could technically run the analysis later but received no results.
>>3) The EV's are expected to have very different values and I do not
>>understand how one could be a combination of another.
>>Any explanation and help would be appreciated,
> Christian F. Beckmann
> Oxford University Centre for Functional
> Magnetic Resonance Imaging of the Brain,
> John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
> Email: [log in to unmask] - http://www.fmrib.ox.ac.uk/~beckmann/
> Phone: +44(0)1865 222782 Fax: +44(0)1865 222717