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Dear Douglas,
Thank you for your guidance.
I am following-up on your response with regards to setting up DODS matrix to test interaction between two continous covariates. If I understand your recommendation correctly (please correct me if I am wrong), I am averegaing slopes for the new interaction covairate (age*weight), while regressing out slope estimates for age and weight. I am curious to know why regressing out the two original covariates is recommended.
Thanks for your time!
David
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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
On 4/13/18 8:02 PM, David S Lee wrote:
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). Myfsgd 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/ /Input001Class1500/ /Input002Class2433/ /.../
I want to test for an interaction between age and weight while controlling forgroup. Instead ofputting-inage 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 tel:%28608%29%20890-1115
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