This is counter-intuitive but reasonable and expected. The distribution
of cluster sizes changes as you change the CFT. When you raise the CFT,
clusters get smaller, but the clusters under the null also get smaller
too. It may be that the smaller cluster size is actually less likely
under the null when using the higher CFT
On 10/30/2024 8:52 PM, 이종훈(보건과학대학 의공학부) wrote:
External Email - Use Caution
Dear Freesurfer expert,
I hope this email finds you well. I am currently working on a project
involving FreeSurfer's cluster-wise correction methods, and I
encountered an unexpected result when adjusting the Cluster-Forming
Threshold (CFT) and Cluster-Wise Probability (CWP) values. I would
greatly appreciate your expertise on this matter.
In my analysis, I observed that some regions were not detected when
using a CFT of 1.3 and a CWP of 0.05. However, these regions emerged
as significant when I increased the CFT to 2.0 while keeping the CWP
constant at 0.05. This finding appears counterintuitive, as a higher
CFT typically results in fewer clusters being detected due to the
increased threshold for significance.
Could you please help clarify why this phenomenon might occur?
Specifically:
1. How might the higher CFT (2.0) interact with the CWP (0.05) to
reveal regions that did not appear with a lower CFT (1.3)?
2. Is it possible that the increase in CFT reduces noise or increases
signal clarity in such a way that previously undetected clusters
reach significance?
Thank you very much for your time and guidance. I look forward to any
insights you can provide on this topic.
Jonghun Lee
Master's Student, Advanced Image Processing Technology Lab
Yonsei University
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