Dear Doug, Michael,
Thanks for thinking with me. Following the discussion, it seems to me that
weighting the contrast matrix in our cohort for our question is alright.
Let me describe it again:
- The diseased population typically consists of 75% female.
- We have three groups (HC, diseased withou
Thanks to both Donald and Michael for catching my mistake about
recommending sample-size weighting within the contrast (both responses
are below). Depending upon the hypothesis being tested it is ok, but
you're probably not going to be in a situation in which you will want to.
doug
--
Hi Martijn, yes, that is a good thing to do!
doug
Martijn Steenwijk wrote:
> Hi Doug,
>
> Thanks for your reply again. It's getting more and more clear now.
>
> I've however one question remaining, which is regarding the correction
> for sex. What I did not tell (my fault ;-) ), is that 75% of t
Hi Doug,
Thanks for your reply again. It's getting more and more clear now.
I've however one question remaining, which is regarding the correction for
sex. What I did not tell (my fault ;-) ), is that 75% of the cohort is
female. Comparing the sex-corrected results with male-only and female-only
Hi Martijn, sorry for the delay. Your contrast matrices look correct.
The differences between demeaning and not demeaning is somewhat
expected. When you do not demean, you are testing whether there is a
difference between groups at age=0 (ie, birth). When you demean, you are
testing for a dif
Dear Doug,
Thanks again for your reply. Based on that I did some further work.
I first demeaned the age of all subjects. Actually, I have a third group
which I would like to compare to, so my contrast matrices will be
[.5 .5 -.5 -.5 0 0 0 0 0 0 0 0]
[0 0 .5 .5 -.5 -.5 0 0 0 0 0 0]
[.5 .5 0 0 -.5
Yes, that is correct, though I think your matrix should be [.5 .5 -.5
-.5 0 0 0 0]. You should also remove the mean from the age (mean
computed from all subjects). Or even better, first test whether there is
a group difference in age slope with [0 0 0 0 .5 .5 -.5 -.5]. If there
is nothing that
Dear all,
I'm relatively new with Freesurfer, but slowly getting more and more used to
it's great possibilities. To be 'sure', I've a question about the design of
a GLM.
I want to compare CT in Healthy Controls vs Diseased, and control for age
and sex. It appears to me that factors (eg sex
