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

History of AFNI updates  

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September 14, 2005 01:16PM
Hi Hedvig,

> So in the difference analysis I assume it will assess
> differences in direction (e.g., activation in grp 1,
> deactivation in grp 2).


No, it seems that -expr 'step (a-a_threshold) - step (b-b_threshold)' would give you the following:

if the value at a voxel is 1, activation in group 1 but no activation in group 2;
if the value is -1, activation in group 2 but no activation in group 1;
if the value is 0, both groups are either active or inactive at the same time.

> If I want to assess differences also in magnitude (e.g.,
> strong activation in grp 2, weaker but significant
> activation in grp 2), does it make sense to remove the
> "step" function and only do for example
>
> -expr '(a-a_threshold) - (b-b_threshold)' ?


Well, it does give you sort of the significance difference between the two groups, but the problem is how to interpret the result: the difference between two t distributions is an unknown statistic.

Gang
Subject Author Posted

Conjunction/Difference analysis

Hedvig September 13, 2005 03:45PM

Re: Conjunction/Difference analysis

Gang Chen September 13, 2005 05:14PM

Re: Conjunction/Difference analysis

Hedvig September 13, 2005 05:58PM

Re: Conjunction/Difference analysis

Gang Chen September 14, 2005 01:16PM

Re: Conjunction/Difference analysis

Hedvig September 14, 2005 04:24PM

Re: Conjunction/Difference analysis

Hedvig September 14, 2005 05:34PM

Re: Conjunction/Difference analysis

Gang Chen September 14, 2005 05:58PM

Re: Conjunction/Difference analysis

Hedvig September 15, 2005 11:09AM

Re: Conjunction/Difference analysis

nadine October 31, 2005 03:32PM

Re: Conjunction/Difference analysis

Gang Chen October 31, 2005 03:44PM

Re: Conjunction/Difference analysis

nadine October 31, 2005 04:58PM

Re: Conjunction/Difference analysis

Gang Chen October 31, 2005 05:23PM