Re: [Freesurfer] FSGD design for multi-centre study

Thanks for your help. I've noticed, however, that 2 of the centres contribute a smaller number of subjects and don't in fact have any female controls. Should I remove these as classes (ie. take out control_Female_centre1 and control_Female_centre2) and then change the subsequent contrast file to look like: 1 1 1 1 1 1 1 1 1 1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 0 Or would this be a problem since now the number of classes that are controls or patients are uneven (10 vs. 12)?

Thanks again, Colleen

--- Colleen Rollins, PhD Candidate Department of Psychiatry University of Cambridge Herchel Smith Building, Robinson Way, Cambridge CB2 0SZ

On 2018-04-09 14:50, C.P.E. Rollins wrote:

Hi Douglas,

Thanks for your response. I just wanted to confirm how the FSGD and contrast files might look for the multicentre study. If I'm to create a separate class for each combination of diagnosis, sex, and center, would there then be 24 classes? (as there are 2 diagnoses (patient vs. control), 2 sex, and 6 centres). For instance: GroupDescriptorFile 1 Group control_Male_centre1 Group control_Female_centre1 Group control_Male_centre2 Group control_Female_centre2 Group control_Male_centre3 Group control_Female_centre3 Group control_Male_centre4 Group control_Female_centre4 Group control_Male_centre5 Group control_Female_centre5 Group control_Male_centre6 Group control_Female_centre6 Group patient_Male_centre1 Group patient_Female_centre1 Group patient_Male_centre2 Group patient_Female_centre2 ...

Then, my contrast between patients and controls would look like 1 1 1 1 1 1 1 1 1 1 1 1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 0 for a doss model, if I'm additionally controlling for age, or 24 zeros (instead of 1) for a dods model? Moreover, should I expect any issues with using such a high number of classes?

Thanks again, Colleen