Dear Julia,

First regarding the error message thanks for reporting this, this was actually a bug in rex and I have fixed that for the next release of the toolbox (in the meantime I am attaching a patch for version CONN14i, simply copy the attached file in your conn distribution folder overwriting the file with the same name there). 

Regarding question (1), it is not necessary to orthogonalize your covariate to the 'All' covariate (the results will be identical whether you do or not), and your regression analyses looking at the effect of your covariate are always considered orthogonal to the whole sample average effects, so you do not have any circularity issues there.

Regarding question (2), rather than simply using more liberal thresholds for your new/limited search volume, the more appropriate way to do this would be to use 'SVC' (small volume correction) and selecting your mask image there to obtain statistics that already take into account this smaller search volume (e.g. DMN areas) when applying the corresponding multiple-comparison corrections (e.g. FWE- p-values)

Regarding question (3), if you extract your data from regions that have been defined by the same (or a non-orthogonal) contrast that you are then trying to evaluate (and from your description I take that this was the case here), then yes, you will have a circularity issue there, and you may assume that the resulting measures will be biased (overestimating effect sizes, under-estimating p-values, etc.) Some times you wish to do just that, for example as a descriptive post hoc analysis, and that is perfectly fine (you just need to acknowledge the limitations and potential biases of the resulting measures, and do not use these tests as any form of confirmatory analyses). If your goal, on the other hand, is to obtain accurate effect-size measures within your regions of interest then I would probably suggest using a cross-validation approach to do this. 

Hope this helps
Alfonso



Originally posted by Julia Landsiedel: