You have to use it on both. The cluster p-value is initially computed without regard to the number of hemispheres. This value is then corrected based on the number of spaces.

On 07/08/2016 08:39 AM, Arkadiy Maksimovskiy wrote:

Hi Everyone,

I was wondering if someone might know whether it is necessary to use the flag "2spaces" on both the left and the right hemisphere?

If I am understanding correctly, this flag corrects for a specific multiple comparison of two hemispheres. Thus, it seems like it would only be necessary to only use it once, because if used on each hemisphere, we would be "penalizing" our results more than necessary- thus being too conservative. If we already correct for using two hemispheres once, then why correct a second time?

If it is only necessary to use it on only one of the hemispheres, would this run the risk of unfairly biasing our results (i.e. more conservative on one hemisphere and more liberal on another)?

Thank you for your help in clarifying this,

• Arkadiy

---

Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer