On 3/29/14 3:09 PM, Ashley Shurick wrote:

Hi,

I have some questions about using monte carlo sim in qdec:

First of all, I just want to verify it's ok to use the simulation with a whole-brain analysis and not just an ROI analysis.

yes

Second, I'm a bit confused about how to calculate the p-threshold for my max clusters. Looking here: http://surfer.nmr.mgh.harvard.edu/fswiki/FsTutorial/GroupAnalysisClusterSummary

tells me how to calculate the p-value of my clusters, but according to the page, max = -log(base10) (pvalue). The example given is the 13th cluster where max = -5.981, and the stated p value is p < .006. I can't figure out how you came up with this p-value, can you please clarify your calculations?

This is not the cluster-wise p-value, this the most significant vertex inside the cluster. This p-value is computed from the GLM and contrast that you supply. The cluster p-value is in a different column in the table.

Finally, in qdec when I change my "threshold" from say 1.3 (.05) to 2.0 (.01) I notice the CW Pvalue threshold doesn't change in the terminal output, and remains at .05. Can you please explain this? What exactly am I changing when I change the "threshold" in qdec?

That is the vertex-wise threshold. You need to explicitly change the CWP threshold in the qdec GUI
doug

Thank you in advance for your assistance,

Ashley

--

Ashley A. Shurick
Ph.D. Candidate

Department of Psychology

Stanford University
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