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Anisha Keshavan edited In_the_paper_scaling_factor__.tex  over 8 years ago

Commit id: f99dd16ffb068ee3cb928e54621cb6db5609a25e

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In the paper, scaling factor estimates were compared for subcortical gray matter volume, white matter volume and total gray matter volume, because these were specifically edited, and because they are the most relevant for future studies on MS and genetics that this consortium is proposing. The largest difference between scaling factors between healthy controls and MS was for white matter volume, and a two sample t-test between the scaling factors yielded a p-value of 0.88. In the paper, the following was added:  "Even though this study calculated scaling factors from healthy controls, we showed that scaling factors derived from an MS population were very similar or identical to those derived from healthy controls. The largest difference in scaling factors between HC versus MS patients was for white matter volume, where $a_{MS} = .967$ and $a_{HC} = .975$. A two-sample T test between the scaling factors resulted in a p-value of $.88$, showing that we could not detect a significant difference between scaling factors between HC and MS. This part of the study was limited in that we only scanned patients at two scanners, while the healthy controls were scanned at 20. However, the similarity between scaling factors for the subcortical gray matter, cortical gray matter and white matter volumes between the MS and HC populations suggests that, given careful editing of volumes on the disease population, the independence assumption holds for MS. For researchers studying other diseases, it may be useful to scan healthy controls and patients before and after an upgrade or sequence change to test the validity of the independence assumption."