You need to put in age, weight, AND age*weight. If you have two classes and use DODS, then the contrast would be

0 0 0 0 0 0 0.5 0.5

Hi Douglas, 

Thank you for your reply. 

To follow up, I am setting up GLM analysis with 1 categorical variable and 1 continuous variable (age X weight). My fsgd looks like this:

GroupDescriptorFile 1

Title Cortical Thickness Interaction between Age and Weight

Class class1 plus blue

Class class2 circle green

Variable           Demean Age X Demean Weight

Input 001 Class1 500

Input 002 Class2 433

...

I want to test for an interaction between age and weight while controlling for group. Instead of putting-in age and weight separately, I multiply them to test for interaction. Can you tell me if following contrast vector will correctly test for this? 

0 0 0.5 0.5

Thank you for your time, 

--

David S. Lee

Associate Research Specialist

Center for Healthy Minds

University of Wisconsin - Madison
(608) 890-1115  

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