You definitely do not want to demean within group. Having said that, no
demeaning method is more "sound" than the other. The problem is in the
interpretation. Imagaine you have a plot of volume vs ICV for each
group. When you have an interaction, the best-fit lines will intersect
at some ICV. I
Yes, I agree completely. We are using DODS and it is clear that we have
different results depending on which type of ICV we use. The question is...
which type of ICV correction for DODS is the most statistically sound?
demean across all groups, no demeaning, or demean within groups separately.
Wha
If there was not an interaction between group and ICV, I would say to
use DOSS where demeaning does not make a difference. Since there is an
interaction, you have to use DODS, but the interpretation is no longer
easy. If you do not demean, then you are implictly testing for a
difference at ICV=
Sorry for not specifying. Yes, we are looking at difference in volume
between the two groups using DODS. What is the most statistically sound...
raw values, demeaning across the entire sample, or demeaning with groups
separately? FYI, I exported the ICV values to SAS and there is a
significant diff
not sure what you are testing, but if you are, eg, looking at the
difference between two groups regressing out ICV, then it can make a
huge difference
On 08/29/2016 12:36 PM, Corinna Bauer wrote:
> Hello all,
>
> I am wondering why results would change completely for between group
> volume ana
Hello all,
I am wondering why results would change completely for between group volume
analysis when using demeaned/mean-centered ICV compared to using ICV as a
covariate in mri_glmfit? See the figures below.
Does demeaning the covariate inherently change the results comapred to the
raw covariate
