Hi Zrinka,
Wrt registrations and background image, yes if you are only re-running
higher-level analysis then the old registrations will have gotten used and
not rerun. The background image may have changed because I think we added
in between the current and previous versions a flag to normalise the
background images to all have the same mean intensity before averaging -
just a display nicety, really.
Wrt the stats, which "old" version are you comparing with? If it's 3.0
then maybe this is answered at:
http://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind0310&L=fsl&P=R5762&D=0&H=0&I=-1&O=T&T=0
and
http://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind0403&L=fsl&P=R517&D=0&H=0&I=-1&O=T&T=0
?
Cheers, Steve.
On Wed, 23 Jun 2004, Zrinka Bilusic wrote:
> Hello,
>
> recently I decided to rerun group analysis on some old data. The reason
> was that the original group analysis was done using the old version of
> Feat, and I wanted to see the additional reports from the new version
> of Feat (the Summary of low-level registration and masks). So I loaded
> the design.fsf into Feat, changed the output directory, verified that
> everything is OK, saved and run. But the (statistical) results are
> different. No only in the report, but I also subtracted zstats images -
> and there are big differences. I inspected the design.fsf files, and
> the only difference I could find (apart from the obvious differences in
> the layout for new and the old versions) is that in the new design.fsf
> file, the degrees of freedom to standard image was set to 7, whereas in
> the old one it was 12. But that should not cause any problems because
> the registrations were already calculated in the single subject
> analyses, and the first step of the group analysis just applies those
> transformations - right?
>
> Also, I notices that the background image for the two analysis looks
> quite different - even though in both design files it was set to the
> "mean highres". I looked at the log files and the commands executed to
> create those seem to be the same.
>
> Am I missing something? The statistical results should not be
> different? Is there anything else I should be checking? by the way, the
> single subject analyses were not changed after running the initial
> group anlaysis...
>
> thanks
>
> zrinka
>
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
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