Hi,
This Z value is the arbitrary cluster-forming threshold and the corresponding p-values are uncorrected, voxelwise p-values and are not related to the cluster-based multiple-comparison-corrected p-values derived later. The choice of this value is completely arbitrary (up to some limits). See the FSL Course lectures, wiki, and GRF papers for more information.
All the best,
Mark
On 6 May 2014, at 05:54, "Yang, Daniel" <[log in to unmask]> wrote:
> Dear FSLers,
>
> When specifying a Z value for cluster thresholding, the default value is 2.3 (which equals to p<.01, one-sided). I am wondering what the theoretical basis is for this default value. How is it compared to using Z=1.96 (which equals to p<.05, two-sided)? Or is it the case that two-sided does not make sense in this context of finding contiguous clusters?
>
> Thanks!
> Daniel
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