If you want to test for an interaction between Age and Weight, you need to create a new covariate which is Age*Weight, then test the sig of this covariate. I would demean Age and Weight for both the inidvidual covaraite and before computing the product.

On 04/12/2018 12:35 PM, David S Lee wrote:

Hi FreeSurfer Experts,

I have two groups (Male and Female) and two covariates (Age and Weight). I want to test change of cortical thickness with age and weight, after removing effects of Group. In other words, is there an interaction between age and weight, regressing out the effects of groups.

How can I set up my Design Matrix to test this?

Thank you,

-- David S. Lee Associate Research Specialist Center for Healthy Minds University of Wisconsin - Madison (608) 890-1115 tel:%28608%29%20890-1115

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