Dear FreeSurfer Experts,

We are trying to run a between group analysis (1 patient group 1 control group) within qdec. We are interested in investigating age-related thickness differences between groups.  Our fixed factors are ‘group’ and our continuous covariate is ‘age’. We would like to control for other possibly confounding variables which should be declared as “nuisance factors, is that correct?

Here is our problem. We like to put down “disease burden” (years subject has had the disease) as our nuisance factor, since it is likely possible that this has an effect on cortical thinning in our disease group. Yet, when we run the model, qdec crashes. Is this because the subjects in the control group have a “0” as disease burden?

Could you advise us on another way of controlling for disease burden?

Cheers,

Catherine