Dear Freesurfer developers,

I had a small confusion while performing a paired analysis.
An analysis is to be performed to examine or analyze the structural differences between two group 'Control' and 'Patient' subjects.
If my study is age and sex matched,
say there is a control with same age and sex for every patient,
How should I plan my analysis on QDEC,

I am currently following this pattern,
Fixed fatcor :- Diagnosis (normal or patient)
Continous factor :- Age 
Nuisance factor :- Total ICV

Is this a correct design? or should I add sex  to the fixed factor,
i.e, fixed factor :- Diagnosis & Sex 

How will my analysis vary with and without using sex as fixed factor ?
Which is the correct design? 
--