On 5/2/2020 7:27 PM, Meike Hettwer wrote:

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Hi doug, thanks for the quick response! I‘m not quite sure if I‘m getting the second part right- could you please elaborate a bit what you mean by „When there is only one numerator DOF, then the sig map is signed by the sign of the contrast (but the p-value is still based on an unsigned test).“ ?

It appears counter intuitive to me to visualize the results of a correlation analysis in a F map...

The F test is a ratio with a numerator and denominator, each has a DOF. If the numerator DOF > 1, then a sign does not make sense (ie, the sign is always positive). If the numerator DOF=1, then F = t^2 and you can give it a sign based on the sign of the t.

As I am mainly interested in the results if a (partial) correlation, I was wondering if there is a way to create a correlation map (e.g. based on the pcc.mgh overlay) that is masked by clusters surviving multiple comparisons corrections? (Monte carlo/ permutation)

Yes. The multiple comparisons correction will create a map of the clusters. You can use mri_mask to make the pcc.mgh map so that you only see the clusters

Thanks again, Dorothee

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On 3. May 2020, at 00:36, Douglas N. Greve dgreve@mgh.harvard.edu wrote:

A t-test is just F test with one DOF in the numerator -- they come out with the exact same p-value (assuming an unsigned t-test). When there is only one numerator DOF, then the sig map is signed by the sign of the contrast (but the p-value is still based on an unsigned test).

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On 5/2/2020 5:32 PM, s7675854@stud.uni-frankfurt.de wrote: External Email - Use Caution

Dear Freesurfer experts,

I have a beginner question regarding fsgd and mtx files. For example, if I have one group and am interested in the correlation between some test score and cortical thickness/surface area, controlling for age and intracranial volume.

I would have 1 group and 3 covariates, e.g.

class 1

score age icv

subj1 1 55 20 3333

subj2 1 43 24 3333

Now if I am interested in the correlation between the test score and an anatomical parameter, I would go with the design matrix:

0 1 0 0 (doss). My question is, why does this calculate an F test, if I am only interested in one group? (I would understand a t-test with test-score slope >0, but where does the F come from?)

I am drawing a mental blank here and would appreciate your help!

Thanks a lot,

Dorothee

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