Two sample t-test with equal variance with the single subject as 1
group and the Probands as the other group. Contrast: 1 -1 or -1 1
depending on the direction of the change.
A one-sample t-test against 0 won't work with Jacobians because they
are centered around 1. Either a log transform or a percent change
calculation for longitudinal studies is needed to change them to be
centered around 0.
On Friday, February 4, 2011, Christoph Berger
<[log in to unmask]> wrote:
> Dear SPMers,
> I have a question regarding a case study of morphometric abnormalities of a single subject compared to a group of probands.
> I have measured an t1 image from every subject and segmented every subject with the vbm8 toolbox into grey and white matter and calculated from every subject the map of the Jacobean determinates. I would like to know, whether the Jacobean from a particular subject differs from the group.
> I would like to use a factorial design specification (one sample t) for easy labeling and visualization of possible effects, but I do not know how. I would think of this posibility: one sample t flex fact model tests, whether a goup differs from 0. In my case, to test, whether the group differes from the particular subject I have to substract the jacobean of the particular subject from the each Jacobean in the group bevor I perform the secondlevel one sample t test over the group.
> Would that analysis be correct?
> My actual workaround is as follows:
> 1. I calculate with IMcalc the maps of the voxelwise standard deviations and voxelwise means of the group of probands and use that to calculate the z transformed Jacobean map of the particular proband
> 2. I use MRIcroN and look there for regions where the Z value is extending the significant threshold.
> Is there a better way to look for effects in this case study?
> Many thanks and kind regards,
> Christoph Berger
Best Regards, Donald McLaren
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Office: (773) 406-2464
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