I have read the FreeSurfer Tutorial: Group Analysis, but there are still something I do not quite understand. I want to make comparison of lgi between two groups, namely, normal control group and patient group. I want to regress out gender and age.For example,if I have 4 subjects: nc1 male age=30,nc2 female age=31,patient1 male age=32, patient2 female age=30, how should I create the FSGD file?How should I design the constrast vector? What kind of test does Freesurfer use,F-test or t-test to detect difference region of thickness or lgi on the surface? What should I do if I want to use t-test to detect the difference between two groups? How should I set the option of the command mri_glmfit --sim nulltype nsim thresh csdbasename if I want to set the p-value threshold 0.05?