Dear Freesurfer experts,
I have a quick question regarding the appropriate design (DOSS or DODS) to
be used with QDEC when comparing 2 groups for cortical thickness and LGI
values.
So far I have used DODS first to look for an age-cortical thickness
interaction in both groups. I used the real ages
FreeSurfers,
I have been analyzing my qdec data in version 5.0 and have some interesting
although somewhat confusing results. Basically I have run a very simple
analysis with DODS and DOSS. My discrete factor is group and my covariate is
age, about as simple as can be.
When I look at the results
DOSS should not be used with QDEC as it may or may not do the right
thing. Is it not disabled? What version are you using?
To answer your question, if you want to use DOSS and you're interested
in the diff bet groups, then first test for an interaction between group
and covariate. If that is n
Dear Doug,
thank you so much for getting back to me on this.
I am using Freesurfer version 5.3 with QDEV version 1.4 which gives me both
DODS and DOSS design matrix options. I am a little confused about DOSS in
QDEC as I have read quite a few publications which have used DOSS in QDEC
before. Can
On 6/20/17 10:14 AM, marco mcsweeney wrote:
Dear Doug,
thank you so much for getting back to me on this.
I am using Freesurfer version 5.3 with QDEV version 1.4 which gives me
both DODS and DOSS design matrix options. I am a little confused about
DOSS in QDEC as I have read quite a few publ
Dear Doug,
thank you.
I will go ahead with DOSS through the command line. I did find significant
differences (FDR corrected) with DOSS in QDEC.
Hopefully they will still be present through the command line. It will be
interesting to see if I get the same results.
Sorry but just one more quick qu
On 6/20/17 10:43 AM, marco mcsweeney wrote:
Dear Doug,
thank you.
I will go ahead with DOSS through the command line. I did find
significant differences (FDR corrected) with DOSS in QDEC.
Hopefully they will still be present through the command line. It will
be interesting to see if I get t
Dear Doug,
OK thank you so much for all of your help.
Best wishes
Marco
On Tue, Jun 20, 2017 at 3:58 PM, Douglas Greve
wrote:
>
>
> On 6/20/17 10:43 AM, marco mcsweeney wrote:
>
> Dear Doug,
>
> thank you.
>
> I will go ahead with DOSS through the command line. I did find significant
> diff
Dear Doug,
I have a few final questions, my apologies.
The study I am working on is a retrospective study, which is not ideal. As
a result, although all of the individuals in the study were scanned on the
same 3T scanner, all of the healthy controls have 1.6mm slice thickness and
most of the pati
mri_info --sres file.mgz will give you the slice thickness
you should at least control for the slice thickness by creating a new
binary factor, so if you had 2 groups, you'd have 4 groups (this is the
design matrix not the contrast matrix)
On 6/20/17 11:58 AM, marco mcsweeney wrote:
Dear Do
Dear Doug,
thanks again. I used mri_info --sres orig.mgz (T1.mgz) and got output 1.
I assume this is 1mm thickness?
Also, in terms of using eTIV or total gray matter volume, which do you
think would be the best to use as nuisance factor when looking at cortical
thickness as well as LGI?
Thanks a
On 6/20/17 2:42 PM, marco mcsweeney wrote:
Dear Doug,
thanks again. I used mri_info --sres orig.mgz (T1.mgz) and got output 1.
I assume this is 1mm thickness?
yes
Also, in terms of using eTIV or total gray matter volume, which do you
think would be the best to use as nuisance factor when l
Dear Doug,
thanks again.
Will look into which is the best for LGI (if any).
Best wishes
Marco
On Tue, Jun 20, 2017 at 7:48 PM, Douglas Greve
wrote:
>
>
> On 6/20/17 2:42 PM, marco mcsweeney wrote:
>
> Dear Doug,
>
> thanks again. I used mri_info --sres orig.mgz (T1.mgz) and got output 1.
> I
Hi Chris,
There really shouldn't be a "thickness-age correlation group difference"
result with the DOSS model. I have FS 4.1 (rather than 5.0 on my
system) but running an analogous model, I see that I do indeed get a
verbal "Description" for such a contrast. However, if I compare that to
the "th
Michael,
Thanks for your response. It was helpful. As you suggested the
"thickness-age correlation group difference" under DOSS is meaningless, so I
have ignored that output.
I am currently left with a situation where under the DOSS model I see a
large ageXthickness effect (controlling for group)
Hi Michael,
I doubt that the loss of 1 DOF is causing the disappearance. In both
models, the test for the difference between groups occurs at a
particular age (age=0). This is not a factor in the DOSS model because
the lines for the two groups are forced to be parallel (so the
difference is
Hi Chris,
If you run an ANCOVA model with an interaction (which is what DODS is)
then the interpretation of the group effect is ambiguous because the
"group" effect varies with age. If there is actually a differential
slope between groups, then the p-value of the contrast of the group
means (i.e.
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