On 12/02/2013 09:05 AM, Yolanda Vives wrote:
> Dear FreeSurfer experts,
>
> I am performing a DODS analysis with QDEC to compare cortical
> thickness of patients and controls and I have some questions regarding
> the nuisance factors age and global cortical thickness.
>
> 1.- Should I demean bot
Dear FreeSurfer experts,
I am performing a DODS analysis with QDEC to compare cortical thickness of
patients and controls and I have some questions regarding the nuisance
factors age and global cortical thickness.
1.- Should I demean both variables or only the age?
2.- Which of the following opt
Dear Doug,
Thank you very much!
Sincerely,
Ye
On Tue, Aug 13, 2013 at 11:39 PM, Douglas Greve
wrote:
>
> If x1 and x2 are the same thing, then the equation is non-invertible. If
> they are the not the same variable, then there is no problem. QDEC computes
> all the contrasts for you (but exclud
If x1 and x2 are the same thing, then the equation is non-invertible. If
they are the not the same variable, then there is no problem. QDEC
computes all the contrasts for you (but excludes contrasts with nuisance
variables)
doug
On 8/13/13 3:03 PM, ye tian wrote:
Dear Doug,
I am afraid t
Dear Doug,
I am afraid that I still don't understand why a variable can not be
"covarying" and "nuisance" simultaneously.
If variables x1 and x2 are covarying, they both go into the model
y = b0 + x1*b1 + x2*b2 + err
Is this correct?
Nuisance, however, is related to the contrast, i.e., test hypo
Hi Ye, don't select the same factor as nuisance and covariate. It will
result in an error for sure. The difference between a covariate and a
"nuisance" factor is purely conceptual. By calling something a nuisance
you tell QDEC not to create a contrast related to it.
doug
On 08/13/2013 02:09 A
Dear Freesurfers,
I have a question concerning the "nuisance factors" in the qdec dialogue.
Suppose I have two independent variables x1 (discrete) and x2 (continuous),
and only one observable y. I choose "Discrete (Fixed factor) = x1",
"Continuous (covariate) = x2".
If I further chose "Nuisance f
