Hi Clara,
you would do the analysis of a single time point the same way you'd run a regular glm or qdec analysis on cross sectional data. You cannot use LME as that is for longitudinal data (more than 1 time point per subject, at least for most subjects). Also the two stage model, first reduces to multiple measures in each subject to a single measure (slope of the linear fit). It would not be the right tool for selecting a single time point.
You could for example create a qdec table with the first row fsid timepoint1.long.base for each subject and then use qdec.
If you want to make use of the improved data from the longitudinal image processing, you need to specify the *.long.base directories, so that data is taken from there.
Good luck, Martin
On 12/08/2015 04:24 AM, Clara Kühn wrote:
Dear FreeSurfer experts,
I have a subsample of my longitudinal data with 3 scans per subjects fully preprocessed and would like to start with some simple correlations of thickness at time 1 with behavioral measures and other factors like age.
Is there a way to do that with LME (since I was planning on using that as a method of choice) or is it possible to do that with QDEC? I've prepared my data for both methods (LME and linear two stage model) but if I use the cross.qdec.table derived from the longitudinal data, it uses the registered and smoothed (with mris_slopes) surfaces from the Base, right? So, I would like to know how I can analyzse a single time point within my longitudinal design.
Cheers, Clara