Re: [Freesurfer] QDEC analyses

[xunzhang_hmrrc]

        External Email - Use Caution        

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:&nbsp;"Douglas N. Greve"<dgr...@mgh.harvard.edu&gt;;
Date:&nbsp;Mon, Jun 22, 2020 10:17 AM
To:&nbsp;"freesurfer"<freesurfer@nmr.mgh.harvard.edu&gt;;

Subject:&nbsp;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:
     
                   
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; External Email - Use           
Caution&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; 
                
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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