Hi,
On 20 Sep 2008, at 01:50, Kirstie Whitaker wrote:
> I'm running a TBSS analysis to see if age correlates with FA. All I
> have right now in my GLM design matrix is the subject's age.
>
> Should I use the -D option in randomise? Should I add a column of
> 1s in the design matrix? Do these do the same thing?
Yes, they do the same thing so either is correct.
> Sorry for the rather basic question. Your help is really appreciated!
> An additional question: Why do you suggest only running 500
> permutations rather than the default 5000 in the example on the tbss
> instruction page?
The 500 in the example is up to you - it's 10 times quicker than
running 5000 permutations but is a little less accurate - Tom feels
fairly strongly that one should do 5000 to get good accuracy in
permutation testing - though for _initial_ analyses I often just run
with 500.
Cheers.
---------------------------------------------------------------------------
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
---------------------------------------------------------------------------
|