Devin,
Thanks for the models, it was clear where the mistake occurred.
You can not use group models with only 1 subject. I thought this might
be what you were doing, but you had also mentioned you had a group of
controls.
If you want to compare two scans within a single subject, then you
need to build 1 large first-level model with both scans in the model,
but as separate sessions. Then form a contrast comparing the different
scans.
If you want to compare the difference with that of controls, then you
have several options:
(1) Use larger first level model for all subjects and then use the
contrast and do a two-sample t-test with equal variance of the
difference images;
(2) Use multiple first level models and use a flexible factorial
design with 2 groups, groups should have equal variance.
(3) Use multiple first level models, subtract the 2 con images, then
use a two-sample t-test with equal variance to compare the results.
All of these approaches should yield the same answer.
Hope this helps.
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Thu, Jan 10, 2013 at 1:39 PM, Devin Sodums
<[log in to unmask]> wrote:
> Dear SPM experts,
>
> I am trying to take a patient who has done the same test twice and run a flexible factorial design to see if there are any differences between scans. My end goal is to use the con.img's that would be outputted as another comparison with a group of controls that have also done the test twice. I have gotten the "no significant voxels." message each time I try comparing the single patient's scan 2 to scan 1.
>
> I have used a two-sample t-test, ANOVA-within a subject, and flexible factorial design, and each of them is still giving me the same error. After reading the posts about changing the independence and variance such that non-sphericitiy is assumed, yet I still receive the same message. I have checked the images with checkreg and they are the same dimensions and everything. I have also tried changing the defaults.stats.fmri.ufp to a more liberal threshold (from 0.001 to 0.01 and even to 0.1) but also still receive the same error message.
>
> This is the first time I have tried comparing a single subject's first and second scans, so perhaps I am doing something wrong to begin with? From what I have read, repeated measures analysis is appropriate, and I believe I set it up appropriately as well.
>
> Any advice/help would be greatly appreciated.
>
> Thank you,
>
> Devin
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