AFNI Message Board

Dear AFNI users-

We are very pleased to announce that the new AFNI Message Board framework is up! Please join us at:

https://discuss.afni.nimh.nih.gov

Existing user accounts have been migrated, so returning users can login by requesting a password reset. New users can create accounts, as well, through a standard account creation process. Please note that these setup emails might initially go to spam folders (esp. for NIH users!), so please check those locations in the beginning.

The current Message Board discussion threads have been migrated to the new framework. The current Message Board will remain visible, but read-only, for a little while.

Sincerely, AFNI HQ

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Vincent Costa
November 05, 2008 02:15PM
I realize all of the AFNI issued MATLAB scripts are to be used at one's own risk, but I wanted to raise a question about what seems to be an erroneous calculation in the DF for within-subject contrasts for two independent groups.

I used GroupAna to compare to unbalanced groups A (n=18) and B (n=13) in an experiment with 2 conditions. When you check the header info for the GroupAna output file it lists the DF for condition X versus Y in group B as 29, when it should be 12. If you run the specific contrast of X and Y for group B using 3dANOVA2 and compare the t statistics generated via GroupAna and 3dANOVA2 (see attached image) you can see that there is a discrepancy in the t-statistics, while the mean difference between the two conditions generated through each program is identical.

Vinny
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Subject Author Posted

GroupAna.m Problem: Improper calculation of DF for within-subject contrasts?

Vincent Costa November 05, 2008 02:15PM

Not really a problem

Gang Chen November 06, 2008 09:57AM

Re: Not really a problem

Vincent Costa November 06, 2008 10:01AM