dear *,
This was precisely my question too. I tried doing the analysis on
patients with known lesions, and in all our test cases, the analysis
brought up those very regions above a significant height threshold. Not
being much of a statistician myself, the end justified the means. But
obviously, a few mails related topics forced me to think that there was
something deeper about the validity of the choosen tests, even if they
yeilded the desired results, and i really wanted to know that. It is a bit
difficult to communicate the data etc on to the list. My question to the
SPM community was: given a data set with particular characterstics, how
does one go about selecting an analysis. Further, how should one validate
the analysis, provide proof that it actually works?. And also, how does
the population of groups affect the analysis?
I hope i have been able to put the questions correctly.
regards, and thanking you all,
Siddharth.
On Tue, 14 Aug 2001, <Hamte zhang> <Hamte zhang> wrote:
> Hi ,spmer:
>
> Siddharth Srivastava([log in to unmask]) asked john a question(Fri, 3 Aug 2001 13:04:54). The content as follow:
> <<<
> dear John, spmers,
> I had the following questions regarding the statistical
> tests for a particular experiment i am doing now. My data consists of
> certain texture features derived from MRI and segmentation maps, which are
> combined in a single number at each voxel. I wanted to compare these
> responses across a group of normal controls, and get a spm of where these
> values significantly differ in the patient.
> Currently i am using "1 scan/subject Ancova", with one
> group containing the normals, the the second group containing a single
> patient. The volumes are normalized and smoothed at 8mmFWHM.
> My question to the group is, is this a correct analysis
> for the comparison?
> Further, i have observed the following. The way the
> texture features are generated yields a sparse volume, and there are cases
> where the values are zero/near zero at that voxel across all normals, and
> substantially large in the patient. But these seem to get excluded from
> the analysis. How does spm deal with those voxels where the response
> variables are zero everywhere in the normals, but large in the patients?
> And, how can i ensure that all the voxels within the brain get analysed?
> I hope i have been able to put the question clearly.
> thanking in advance,
> Siddharth.
> >>>
> john's response were:
> <<Without seeing your design matrix or data, I couldn't say if "1 scan/subject Ancova" was correct or not.In terms of defining the region of the image that gets analysed, you need to use explicit masking, whereby you provide an image defining the region you want to search. Zero or NaN values identify voxels that are not included in the analysis.>>
>
> >From above message ,I know Siddharth wanted to make analysis by comparing a single patient with a control group (several persons).. I wonder wether SPM can make analysis by comparing a single patient with a control group (several persons)? If can ,how ?
>
> Many thanks.
> Hamte.
> 01-8-13
>
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