The two covariates (in theory) will account for some of the variance by themselves. You could get some bias if you don't includ ethem
On 05/03/2018 03:33 PM, David S Lee wrote:
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 _____________________________________________
You need to put in age, weight, AND age*weight. If you have two classesand 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 variableand 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 whilecontrolling forgroup. Instead ofputting-inage and weight separately, Imultiply them to test for interaction. Can you tell me if followingcontrast 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> _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu <mailto:Freesurfer@nmr.mgh.harvard.edu> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer <https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer>_______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu mailto:Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
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