Yes, you should see cyan. Note that you would see cyan if group1 slope is 0 and group 2 slope is positive. Probably not a problem with age, but it is just something to think about.
doug

On 2/17/14 1:38 AM, Yang, Daniel wrote:

Dear FreeSurfer developers and experts,

If I have a binary factor (Group1: patients, Group2: controls) and a continuous variable (age), I know I can follow Contrast2 in the following wiki to test the interaction effect.

http://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf2G1V

Contrast2: [0  0  1  -1]  tests if Age slope in patients (Group1) > controls (Group2), and if Age slope_Group1 - Age slope_Group2 > 0, I can see red/yellow.

For example, cortical thickening is accelerated in patients (vs. controls).

I am wondering how I can test for whether cortical thinning is accelerated in patients (vs. controls)?

Here, the slope for Age would be negative. And if cortical thinning is accelerated in Group1 (vs. Group2), I should observe Age slope_Group1 < Age slope_Group2, that is, Age slope_Group1 - Age slope_Group2 < 0, thus, I should expect to see blue/cyan?

Best,

Daniel

-- 

Daniel (Yung-Jui) Yang, Ph.D.

Postdoctoral Researcher

Yale Child Study Center

New Haven, CT

Tel: (203) 737-5454

E-mail: yung-jui.yang@yale.edu

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