Dear Freesurfers,

I'm doing a longitudinal analysis of cortical thickness using the newest version of Freesurfer and there is something i would like to ask you all.

I have two time points and only one group of patients.

I've finished the pre-processing and am now searching for differences between the two time points using Qdec.

Since i only have one group my cross.qdec.table.dat file looks pretty much like this:

fsid         years
template_M_b01 0.665
template_M_b02 0.665
template_b03        0.71
template_b04        0.79
template_b05        0.915
template_b07 0.665
template_b09 0.625
template_b10 0.625
template_b11 0.71
template_b13 1.04
template_b14 0.71
template_b15 0.665
template_b16 0.835
template_b17 0.665
template_b18 0.625
template_M_b19 0.71
template_M_b20 0.625
template_b21 0.71
template_b22 0.585

I selected the long.thickness.rate in Qdec interface and years as continuous covariate since it is the only variable that i have in my cross.qdec.table.dat (no groups or other covariates of interest). 

My question is: Is this the analysis i should be doing given that i want to know the differences between time point 1 - time point 2? 

Many thanks,

Joana