help > RE: Network Based Statistics
Sep 12, 2017  01:09 PM | Ekaterina Pechenkova
RE: Network Based Statistics
Dear Alfonso,

sorry for a delayed follow-up. This time I played a little bit with the contrasts and the NBS in another project and found that NBS just hangs with some contrast specifications. I had two groups (Treatment and Control) and one covariate of no interest (Age), and two conditions (Pre and Post). So if I specify between-subject contrast as [1 -1 0] and between-condition contrast as [1 -1], then go to the ROI-to-ROI results explorer, select the ROIs, the two-sided contrast and hit the Enable permutation test button, the results are there in a minute or so. However, if I specify ANOVA as [1 -1 0; -1 1 0] between-subjects and/or [1 -1; -1 1] within-subjects when it comes to the permutations, the toolbox just hangs. Does it mean that only one way of the contrast specification is applicable for the NBS? In other respects the two models seem to be equivalent, do not they?

I use the Conn 17.a with SPM12.

Thank you.

Best,
Ekaterina.
Originally posted by Alfonso Nieto-Castanon:
Dear Ekaterina,
NBS statistics are appropriate for F-contrasts as well. Both of the contrast specifications ([1 -1;-1 1] or [1 -1]) will work exactly in the same way (assuming that you are specifying "two-sided" effects for the T-contrast if you are using the latter)
Best
Alfonso

Originally posted by Ekaterina Pechenkova:
Dear All,

a follow-up question re NBS: do I understand it correct that the NBS statistics are only appropriate for testing T-contrasts, but not F-contrasts?

I.e. if I have two groups and two conditions and want to look at the 2x2 interaction at the network level, can I test contrast [1 -1; -1 1] (subject effects) with [1 -1; -1 1] (condition effects), or should I rather specify a contrast like [1 -1] (subjects effects) [1 -1] (condition effects)?

Best,
Ekaterina.