Dear Doug,

Thanks for the reply.

Would you recommend using pos or neg sign, instead of abs for a group comparison?

Are my vertex-wise results showing true differences between controls and patients even if the mean thickness of the clusters is not statistically different? Or should i just consider the clusters that have statistically different mean thickness between groups?

Many thanks

2010/8/3 Douglas N Greve <greve@nmr.mgh.harvard.edu>
It might be, it depends on how you defined the sign of the voxel-wise threshold. If you used "abs", then it is certainly possible.

doyug

Joana Braga Pereira wrote:
Dear all,

I would like to ask you whether there should be an exact correspondence between vertex-wise thickness and mean thickness of clusters.

I'll explain you my problem.
I did an analysis with 2 groups and 2 covariates. Then i run the mri_glmfit script and found clusters of greater thickness in controls compared to patients. When i extracted the mean thickness of these clusters and did a two sample t test i observed that the controls had greater thickness than patients, however not statistically significant, even after including in this analysis the 2 covariates.

Is this normal? How does freesurfer uses the covariates when performing an analysis?

Many thanks
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