For the interaction it would be
0.5 -0.5 -0.5 0.5
On 5/9/17 8:32 AM, Laura Ferrero Montes wrote:
Thank you for the information. I just want to be sure if I have understood it properly. If I had two groups and two sites, my design matrix would be like:
GroupDescriptorFile 1 Class PatientsGroup1 Class PatientsGroup2 Class ControlsGroup1 Class ControlsGroup2
If I want to test for the effect of group, contrast matrix would be: 0.5 -0.5 0.5 -0.5
If I want to test for the effect of site, contrast matrix would be: 0.5 0.5 -0.5 -0.5
Finally, in case of interaction test, how contrast matrix would be?
Douglas N Greve greve@nmr.mgh.harvard.edu escribió:
You should make sure to have a balanced design (ie, approx the same pats and cons at each site). Then include site as a regressor, ie, if you had two groups and two sites, you would have four regressors. You could then test for the effect of group, the effect of site, and the interaction. If there is an interaction, then it is hard to interpret the differences between groups.
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