For our purposes we can calculate all the necessary information knowing and this can be approximated by

where is an estimate of the smoothness of the GRF, the number
of dimensions in the GRF and is the number of *in-brain*
voxels.

The probability of clusters in this *excursion set* is
approximated by a Poisson

(3) | ||

(4) |

The number of voxels comprising a cluster is distributed according to

where

We can calculate [3] by calculating the product of and summed over

(7) | ||

(8) | ||

(9) |