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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Gang Chen
March 25, 2009 04:38PM
> I assume this difference is due to differences in df when running the between
> group vs. within group analysis. Is this correct?

In addition to the difference in the degrees of freedom, GroupAna uses the pooled variance to calculate the statistics. In other words, the data from group B are also involved in computing the statistics for the contrast for Condition1 in Group A.

> Which way is the more appropriate way to describe the within group differences?

GroupAna uses more data in modeling, but also bears an assumption. For example, for this specific contrast, it assumes the variability of the contrast within group B would be roughly the same. If this assumption doesn't hold, the 3dANOVA3 result would be more appropriate.

Gang
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Comparing within subject contrast in GroupAna with results from 3dANOVA2

Laura March 25, 2009 01:44PM

Re: Comparing within subject contrast in GroupAna with results from 3dANOVA2

Gang Chen March 25, 2009 04:38PM