Hi Philip, the p-value for the cluster is not computed from a t or z. It is computed from a simulation in which random noise is generated on the surface, smoothed, clustered. The maximum cluster size is found. This is repeated 10000 times to give a list of 10000 cluster sizes. The p-value for a given cluster in your analysis equals the number of clusters in the list whose area is greater divided by 10000. dopug

On 5/17/13 9:46 AM, Kelly, Philip wrote:

Dear Freesurfer list members,

Within QDEC I have found a number of clusters that show significantly different cortical thickness and local gyrification between two groups.

The cluster summary exhibits the p value, coordinates and other information regarding the cluster, however I wanted to report the t or z values and was unsure in finding or computing this from QDEC.

The p-value must be computed from one of these scores but I could not find it to be reported in any of the output.

Searching on the mailing list and tutorials, I could not find an easy solution to this.

Thanks for your time and I look forward to hearing back.

All the best,

Philip Kelly

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