Dear Bob,
Thank you for your reply and for pointing out the issue of averaging correlations related to non-linear transformations.
Is there any way to actually derive the "mean of correlation" to threshold the maps at r=0.3?
From what I understand after discussing this with my supervisor, there are (at least) these three options:
- Use 0th sub brick showing mean of arctanh(correlation) as input for 3dcalc -expr 'tanh(a)'
- Convert r=0.3 into arctanh(correlation) using ccalc 'atanh(0.3)'
- Run 3dGroupInCorr with the -sendall option to derive the individual arctanh(correlation) maps, then transform them back into correlation values using 3dcalc -expr 'tanh(a)', then average untransformed correlation values
From experience with behavioural data and meta-analyses, my supervisor said that there no option is necessarily preferable. Is there any recommendation you could give based on your experiences with fMRI data? My dataset consists of 50 subjects with 600 time points.
Many thanks and best regards,
Stef
