Hi,
We noticed that running 3dClustSim on two different masks resulted in higher cluster thresholds for the smaller mask (237709 voxels) than the larger one (246932 voxels). The acf values were very similar (they came from the same sample), but just to test it I ran the 3dClustSim command for the smaller mask with the acf values from the larger one, and this lowered the thresholds only a little bit, so does not seem to be accounting for the discrepancy.
Shouldn't the smaller mask have lower cluster-size thresholds? Any ideas about what might be accounting for this?
Thanks,
Kara