"The primary concern is that a group change in a specific tract may be erroneously interpreted as an effect in a crossing-fibre pathway."
I see what you mean–so, consider the following scenario: I have an ROI in which there are significant group differences in FA. In the ROI, these FA differences are more correlated with complexity/count (voxelwise) than they are with FD or FC (fixelwise–ROI analyzed with fixelcfestats + ROI mask).
Does this situation give any leverage to an argument for group differences in fiber organization? Or are there other equally likely interpretations (e.g., free water contribution, noise). If other interpretations are likely, is there a way to follow up on dissecting connectivity in those areas? Any references about this issue would be awesome (I have the 2014 Riffert paper)
"The most important thing is to interpret any observed statistically significant effect within the limitations of the metric being quantified. As long as those limitations are adhered to, there's nothing wrong with this type of analysis. Note that this includes reporting effects as "differences in the 'complexity' metric" as opposed to a more generic "crossing fibres are more/less complex", since the latter is open to subjective interpretation; it requires some care in knowing precisely how different changes in the FOD manifest as differences in the quantified metric, and therefore how changes in the metric may have arisen (and this may be ambiguous)."
Thanks–again, are there methods available for getting more precise about this? E.g., if significant differences in FA are NOT underpinned by fixelwise FD/FC/FDC, but ARE linked to complexity and count across an ROI, how would you (and any others with expertise) interpret such a finding? Again, any references to this effect would be great. I am really excited about this software but I have been somewhat at a loss to explain group differences in FA that are not particularly attributable to FD or FC.