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,
- 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?
- 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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