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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Mike Bello
February 09, 2005 11:17AM
Hi, I apologize in advance if this question is obvious... I have a group with N=17, four conditions (all within-subject). I have two planned contrasts between conditions (1 -1 0 0 and 0 0 1 -1). So, I ran an ANOVA, which gave me [4,64] as dfs for the omnibus. For the contrasts, i get t tests with 64 degrees of freedom.
Now, had I run t tests directly on the pairs of conditions of interest (i.e., without running the ANOVA), the degrees of freedom would have been 16 (instead of 64) for each comparison. So, I'm confused, which one is "better"? What is the rationale for one vs the other? Obvioulsy, I get more activations when I run the contrasts within the ANOVA....
Thanks in advance...
-Mike
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Subject Author Posted

contrast and dfs

Mike Bello February 09, 2005 11:17AM

Re: contrast and dfs

Robert Cox February 09, 2005 11:36AM

Re: contrast and dfs

Mike Bello February 09, 2005 11:48AM

Re: contrast and dfs

Gang Chen February 09, 2005 11:54AM

Re: contrast and dfs

Mike Bello February 09, 2005 12:00PM

Re: contrast and dfs

Gang Chen February 09, 2005 01:16PM