help > RE: ANCOVA rank deficient
Dec 6, 2017  05:12 PM | Andrew Zalesky
RE: ANCOVA rank deficient
You might want to check that you are interpreting the contrast correctly. If you code patients as 1 and controls as 0 (or -1), then the contrast of [0 1 0 0] will give patients greater than controls. Otherwise, if patients are coded as 0 (or -1) and controls as 1, then contrast [ 0 1 0 0] will give controls > patients. 

You might also want to check that your connectivity matrices are ordered correctly.



Originally posted by Juan Pablo Princich:
Dear Andrew, 

I used NBS to compare 2 groups as stated in this post accounting for age and sex differences using a t-test, with a [0 1 0 0] contrast type as you suggest.
I found one component with 6 connection pairs that shall have higher connectivity in patients than in controls as the matrices were arranged in the same way as mentioned in this post (patients first followed by controls).

But i get confused interpreting results because when i extract the identified connections for all participants and perform individual tests (mann withney, non parametric)  on each connection pair between patients and controls , the values on patients are indeed significantly lower than in controls... contrary to the NBS results.


Will really appreciate your comments and possible explanations for this ambiguity.  Please be aware that age and sex effects are not regressed out for the individual connections test, but significance levels ares still very low (p.001).


Sincerely 
Juan P
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RE: ANCOVA rank deficient
Dec 6, 2017