Thank you for your reply. But it says in:
http://www.fmrib.ox.ac.uk/fslcourse/lectures/practicals/feat3/index.htm
under:
Group difference with multiple sessions for each subject
that we should put all the second-level analyses into a single
second-level model when there is a small number of runs for each
subject because if we use one model/subject it would not lead to a
good within subject session-to-session variance. So isn't that a
strong reason to chose the single second-level model?
Thanks again,
Marc
On Sun, Apr 18, 2010 at 12:21 PM, Stephen Smith <[log in to unmask]> wrote:
> Hi - yes, the two are not exactly the same, but I don't think there is a
> strong reason for choosing one versus the other.
> Cheers.
>
>
> On 14 Apr 2010, at 21:21, Marc Bouffard wrote:
>
> Hello,
>
> I think this has been covered in the forums before but I have not found a
> clear answer. What is the recommended way to combine/average fmri runs
> within subjects (following first-level analysis)? For example, if for each
> subject we have 2 fmri runs should we use the method outlined in one
> analysis/one model:
>
> http://www.fmrib.ox.ac.uk/fsl/feat5/detail.html#MultiSessionMultiSubject
>
> or should we have one separate model/analysis for each subject?
>
> I have tried both and get simlar results but the zstats from the latter are
> noisier particularly on the edges of the zstats images. So this suggests
> that the two are not doing exactly the same computations and therefore are
> not answering the averaging question in exactly the same way?
>
> Regards,
>
> Marc
>
>
>
> ---------------------------------------------------------------------------
> 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
> ---------------------------------------------------------------------------
>
>
>
>
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