On 11/10/2020 8:25 AM, Rovai Antonin wrote:
External Email - Use CautionHello,
I am creating sig.mgh overlays in a group analysis. On this map, I can see some blue and red vertices, corresponding to negative and positive values (respectively) on the map.
On the other hand, I read in the documentation that sig.mgh is a map created by computing -log(p) (base 10, whatever).
That cannot be true, since 0<p<1, hence -log(p)>0.
After some exploration I came up with the following guess: sig.mgh is actually -sign(z)*log(p). (That is of course very useful to quickly interpret the maps.)
Question 1: is this guess correct?
Yes, it is, for t contrasts. F contrasts will not have a sign.
Question 2: where is the piece of documentation I missed where this is explained? (I am asking this because I feel like I am missing a lot on the details on the machinery behind FS commands...)
I just updated two of the wiki pages where I found this to be incomplete. Not sure how to answer your question about the machinery. FS is a sprawling, complicated suite of tools. We make all the source code available, so that is the ultimate documentation.
Cheers Antonin
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