Dear Doug,
I am afraid that I still don't understand why a variable can not be "covarying" and "nuisance" simultaneously.
If variables x1 and x2 are covarying, they both go into the model y = b0 + x1*b1 + x2*b2 + err Is this correct?
Nuisance, however, is related to the contrast, i.e., test hypothesis. If x2 is nuisance, then (1 0) * (x1 x2) = 0 Is this correct?
Otherwise, how does one specify the contrast matrix in Qdec?
Thank you very much!
Sincerely, Ye
On Tue, Aug 13, 2013 at 12:03 PM, Douglas N Greve <greve@nmr.mgh.harvard.edu
wrote:
Hi Ye, don't select the same factor as nuisance and covariate. It will result in an error for sure. The difference between a covariate and a "nuisance" factor is purely conceptual. By calling something a nuisance you tell QDEC not to create a contrast related to it. doug
On 08/13/2013 02:09 AM, ye tian wrote:
Dear Freesurfers, I have a question concerning the "nuisance factors" in the qdec dialogue. Suppose I have two independent variables x1 (discrete) and x2 (continuous), and only one observable y. I choose "Discrete (Fixed factor) = x1", "Continuous (covariate) = x2". If I further chose "Nuisance factor = x2", does that imply that
- my contrast matrix is (0 1)
- null hypothesis: Y is independent of x2
Thank you very much! Sincerely, Ye
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