Just wanted to follow up:
For which design types is this test appropriate/inappropriate?
I've found numerous references to the condition number, but none of them have stated any actual
threshold values that are commonly used. How did you arrive at 5e-2? Have you tested
simulated data to see how low you could go before the GLM failed?
On Wed, 20 Oct 2004 09:12:23 +0100, Stephen Smith <[log in to unmask]> wrote:
>Hi Jack. Yes, the program feat_model (which creates the model given the
>design, including outputting the ratio _only if_ it faile test) could be
>recompiled to always output this - you just need to find the relevant
>printf statement and recompile....
>The threshold is currently set at 5e-2 - the reason that we have talked
>about different thresholds is that doing the test the way we do (via the
>ratoi of min to max eigenvalues) isn't appropriate for all design types -
>basically it's just more complicated than that. However, we're just now
>working on a better test which takes into account the contrasts and
>typical noise level etc - so watch this space.
>On Wed, 20 Oct 2004, Jack Grinband wrote:
>> Hi All,
>> What exactly is FEAT's rank deficiency threshold? I searched through the list and various
>> have listed e(-8), e(-6), e(-5), and e(-4) as "conservative" thresholds. There is 4 orders of
>> magnitude between the smallest and largest of these. So, does that mean that the threshold
>> depends on some other factors?
>> Also, I'm having trouble finding the eigenvalue min:max ratio for each analysis. I couldn't find
>> the log or design files. Is there any way I can get this information?
> Stephen M. Smith DPhil
> Associate Director, FMRIB and Analysis Research Coordinator
> Oxford University Centre for Functional MRI of the Brain
> John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
> +44 (0) 1865 222726 (fax 222717)
> [log in to unmask] http://www.fmrib.ox.ac.uk/~steve