Hi Hans,
it is not quite clear to me what you mean by residuals ...
But what randomise does is permuting the design matrix
(exchanging group labels in the design matrix, or flipping the signs)
for N times, and repeating an IDENTICAL mathematical process at each of these N times
(which is fitting the GLM of Y=X\beta+\epsilon; each time the X varies)
and storing the statistic of interest after each permutation in order to form the null distribution.

see
http://www.fmrib.ox.ac.uk/fsl/randomise/
and the cited references please.

Cheers

On Thu, Jul 2, 2009 at 2:34 PM, Hans Tissot <[log in to unmask]> wrote:

Hi FSL experts, 

I have a question regarding randomise residuals. As per my understanding randomise fits the null model only to the data and calculates null only residuals. Then it permutes these null only residuals and adds them back onto the fitted null model to create realizations of null data. My question is:

Are these null only residuals modified (or standardized) in any way before permuting them? If so, exactly how?

Thanks,

Hans Tissot.

--
G. Salimi-Khorshidi,
D.Phil. Student, Dept. of Clinical Neurology, University of Oxford.
[log in to unmask]    http://www.fmrib.ox.ac.uk/~reza
FMRIB Centre, John Radcliffe Hospital,
Headington, Oxford,  OX3 9DU
Tel: +44 (0) 1865 222466  Fax: +44 (0)1865 222717