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Thanks for your timely response.
To assess the two group differences in cortical thickness, whole-brain vertex-wise analyses were performed using the graphical user interface of FreeSurfer known as QDEC. We used a general linear model to compare the thickness between the patients and healthy controls with age and sex as covariates. The Monte Carlo Null-Z Simulation was conducted to control for multiple comparisons (cluster-wise corrected P< 0.05). But, as we all know, QDEC analyses have always be done for the two hemispheres separately, so the multiple comparisons are also conducted for two hemispheres separately, which, the reviewer assumed, is different from multiple comparisons for the whole brain? So, could you please provide some perspective and citation about the validation for such design of QDEC (i.e., the right and left hemisphere were tested separately)?




------------------ Original ------------------
From: "Douglas N. Greve"<dgreve@mgh.harvard.edu>;
Date: Mon, Jun 22, 2020 10:17 AM
To: "freesurfer"<freesurfer@nmr.mgh.harvard.edu>;
Subject: Re: [Freesurfer] QDEC analyses

How you did you do your analysis? As an exploratory/map-based analysis? Or as an ROI analysis? How did you correct for multiple comparisons? Generally, in a map-based analysis, the correction for multiple comparisons incorporates the fact that there are two hemispheres being tested.


On 6/20/2020 10:04 PM, xunzhang_hmrrc wrote:

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Hello Freesurfer developers,

Recently, I have used QDEC of freesurfer 6.0.0 to examine the cortical thickness differences between two groups, and the manuscript has been submitted to a journal. One reviewer raised a question -"The manuscript stated that the right and left hemisphere were tested separately. Could the authors provide an explanation for this? I assume that testing over 68 (all ROIs) vs testing separately left and right (34 ROIs) would have an effect?" Unfornately, I don't know how to responde to this reviewer, so I would like to ask for your help. I just followed the tutorials of QDEC (http://surfer.nmr.mgh.harvard.edu/fswiki/FsTutorial/QdecGroupAnalysisV6.0), and I found QDEC analyses have always be done for the two hemispheres separately. So, could you please provide some perspective and citation about the validation for such design of QDEC?

Thank you in advance for your assistance,

Best regards,


Xun



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