Output Files

[mgogniat]

Hello,

I'm wondering if you could provide me some information on where the output files from each step in the process of completing a voxel-wise mediation can be found (i.e., under what directories?).

Thanks,

Marissa

[mgogniat]

Just following up on this, thanks!

[WeiCheng88]

It would be helpful if the tools could provide the result files of each step, such as the files of correlation between any two variables (X-Y, X-M, and M-Y), rather than the files of mediation result. Thanks in advance.

[trislett]

Hi @mgogniat ,

The indirect effect (SobelZ) from the voxel-wise mediation are in the output directory. The intermediate steps are calculated internally. If you need each step, I recommend calculating them individually using step1-voxel-regress. For instance, if the image is the 'M' variable:

IVAR.csv -> Single column of independent (left) variable (such as diagnosis)
DVAR.csv -> Single column of dependent (right) variable (such as cognitive performance score)
IVARandDVAR.csv -> Two columns of containing IVAR and DVAR

M ~ X + b (Step 1):
tfce_mediation step1-voxel-regress -i IVAR.csv covars.csv

-> {neg}tstats_con1* image is the effect of path A

Y ~ X + M + b (Step 2):
tfce_mediation step1-voxel-regress -i IVARandDVAR.csv covars.csv

-> {neg}tstats_con2* image is the effect of path B ***
*** Note: the M (image) variable and Y (dependent) variable are switched here. That's ok since the tstat is equivalent either way.

Indirect effect:
tfce_mediation step1-voxel-mediation -i IVAR.csv DVAR.csv -c covars -m M

If steps 1, 2, and the indirect effect are all significant, then the mediation effect is valid.

@WeiCheng88
The TFCE transformed T-stats can be calculated as above. The correlations/betas would not be informative because of TFCE.