Hi Doug,
Thanks for your reply. Yes there were areas of significant difference reported in the age slopes maps, after the mri_glmfit command was run. However, I haven't checked to see yet whether there are surviving clusters after correction for multiple comparisons. I see, yes that definitely makes sense especially since the slopes have an opposite sign. However I still had a couple questions:
1) If I did want to look at what the age-corrected trait looked like when compared between the Diseased and Healthy groups at age=mean instead of age=0, what would I need to do?
2) When not including the age in the fsgd file and using a design matrix of [1 -1] I get the significant differences between the average trait in the diseased cases vs the average trait in the control cases. Is there a way to get a summary file with the actual averages along with the significance maps?
Thanks a lot for your help! Panos
Was the difference in the age slopes significant? Ie, and interaction between age and group. If so, then you have to proceed with caution (at least one statistician told me not to proceed at at:) because the difference in the intercepts between the two groups will depend on age making it very difficult to interpret. At the age where the lines intercept, there will be no difference doug
On 03/07/2014 02:57 PM, pfotiad@nmr.mgh.harvard.edu wrote:
Hi Doug,
I ran a group analysis comparing a trait between two groups (Diseased vs Controls) with one continuous variable (age), with the following design matrices [1 -1 0 0] and [0 0 1 -1]. When I loaded the significance map and the descriptor file, the age slope of the trait in Controls was positive whereas the age slope of the trait in the Diseased cases was negative. Therefore, comparing the intercept between the two groups does not really give that much info, since the slopes are of opposite sign. What do you believe would be the best course of action in order to compare the age-corrected traits:
- instead of age=0 maybe comparing the groups at age=mean?
- or going with a DOSS model?
Thank you for your time, Panos _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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