Thanks, Doug. 


There is no significant interaction and I merged the males and females within each group, but the reviewer wants me to include gender as a covariate. Do we always need to control for gender esp. when the group x gender is insignificant? Will that be "over-controlled"?



From: freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edu> on behalf of Douglas N Greve <greve@nmr.mgh.harvard.edu>
Sent: 06 April 2017 20:45
To: freesurfer@nmr.mgh.harvard.edu
Subject: Re: [Freesurfer] QDEC-volume, thickness and area
 
what do you mean they do not differ in gender ratio? Just that the
relative number of M/F is the same in each group? If there is not a
significant interaction between gender and group, then you can usually
merge the genders.


On 04/05/2017 05:13 PM, Lim, Lena wrote:
>
> Dear Freesurfer Experts,
>
> 1) I have 2 groups (A & B), which do not differ in terms of gender
> ratio. If there were no significant regions for Group-Gender
> interaction in mean cortical thickness in the QDEC analysis, can I
> conclude that gender does not influence the effect of group on
> thickness? The differences between A and B on mean thickness is not
> affected by Gender? Is this valid or do I need to add Gender as a
> covariate even though the group do not differ on gender ratio?
>
> 2) A reviewer pointed that it is not right to test for group
> differences in volume once I have tested for thickness and area,
> especially when there is a cluster where A and B do not differ
> significantly in thickness and area but they differ significantly in
> volume…Is this right?
>
> Please kindly advise.
>
> Many thanks,
>
> Lena
>
>
>
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