Absolute vs percent change for correlational tractography

[Hannah Lindsey]

Hello! You have the following stated on the correlational tractography page of the online user manual: 

The “metric” group box allows you to define how the difference is calculated. “scan2-scan1” calculates the difference (recommended), whereas “(scan2-scan1)/scan1” calculates the difference as a percentage of the first scan.

Can you please explain why the absolute difference is recommended over percent change?

Thank you!

Hannah

[Frank Yeh]

The “scan2-scan1” has a uniform systemic noise level, whereas
“(scan2-scan1)/scan1” has large fluctuations if scan1 is close to
noise level.

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[Hannah Lindsey]

thank you!