Thanks for the answer, you were right on the spot.
I now wonder if anyone have any suggestions about how I should set up
my analysis. We have two groups of 20 subjects (patients and controls)
who have performed four tasks during scanning (task1, task2, task3,
task4 scanned as four different runs). We wanted to do the 2nd level
analysis by comparing "task1 vs task2"-contrast, "task1 vs
task3"-contrast etc. in each subject. In the 3rd level analysis we
wanted to compare the patient group's average contrast with the
control group's average contrast. Are on the wrong track here, or
should we just trick FSL by adding a fifth "dummy" run that isn't used
later in the analysis?
Best regards
Hallvard Røe Evensmoen
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Siterer "David V. Smith" <[log in to unmask]>:
> It's probably giving the error because you don't have any degrees of
> freedom. It looks like your model has 4 observations and 4 parameters.
> Presumably, your three-EV model should produce the same error if you only
> provide it with 3 runs worth of data.
>
> David
>
>
>
>
> -----Original Message-----
> From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf
> Of Hallvard R øe Evensmoen
> Sent: Wednesday, July 08, 2009 9:44 AM
> To: [log in to unmask]
> Subject: [FSL] FEAT 2nd level fails when including an additional EV
>
> Data are from four runs in the same subject. First-level FEAT analysis has
> been done on the different runs. The error message shows up when increasing
> to four EVs in a second-level analysis.
> It works smoothly on three EVS, and fails no matter what first-level EPI we
> use in the fourth EV (thus independent of subject or run). We got the same
> error message when running on a different computer with different OS (OS X
> vs Linux).
> ---------------------------------------------------------------------
> Erroe message:
>
> cat ../design.lcon | awk '{ print }' > design.lcon
> /Applications/fsl/bin/flameo --cope=filtered_func_data
> --vc=var_filtered_func_data --mask=mask --ld=stats --dm=design.mat
> --cs=design.grp --tc=design.con --fc=design.fts --runmode=flame1
>
> An exception has been thrown
> nevs >= ntpts, Singular matrix.Trace: Gsmanager::flame_stage1;
> Gsmanager::run.
> ---------------------------------------------------------------------
> The model setup has been attatched.
>
> Does anyone know what might be wrong?
>
>
>
> Best regards
>
> Hallvard Røe Evensmoen
>
>
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