Hello AFNI Gurus,
I am interested in examining whole brain activity associated with a quantitative covariate of interest ("DESB") while controlling for both categorical (e.g., sex, data collection site) and quantitative (e.g., age, "PCL5", "CTQ") covariates of no-interest. I also have two within-subjects conditions in my task ("fearful faces", "neutral faces"). I first ran this analysis using 3dMVM, however, I hit a snag once I wanted to correct for multiple comparisons using 3dClustSim. The data were processed originally in SPM12, and I do not have access to the appropriate residual file to estimate smoothness with 3dFWHMx for 3dClustSim. To get around this, I decided to run my group analysis using a paired t-test in 3dttest++ with the -Clustsim option instead.
Per 3dttest++ instructions, I have coded the categorical covariates numerically using, e.g., 1=Male, 2=Female (see below for an excerpt of my covariates file). Is this the correct numerical coding for categorical variables of no interest in 3dttest++? Or do these need to be dummy coded instead?
Furthermore, I do not want the program to center the categorical covariates, so I have set the covariates -center option to "NONE", and I instead mean centered the quantitative covariates before entering them into my covariates file for use with 3dttest++. Is this the correct course of action?
Thanks for your time and help!
Best,
Lauren
Excerpt from Covariate File Used with 3dttest++:
Subj Site Sex Age PCL5 DES CTQ
sub-100203 2 2 11.34 30.86 1.64 -8.95
sub-100311 4 2 -1.66 -24.14 -0.36 -9.95
sub-100325 2 1 5.34 17.86 1.64 14.05
sub-100458 3 2 17.34 32.86 2.64 -7.95
sub-100459 3 2 -8.66 -9.14 -1.36 -1.95
sub-100491 1 2 -5.66 -13.14 -1.36 -6.95
sub-100676 2 2 -9.66 -17.14 0.64 2.05
sub-100814 1 1 -3.66 -6.14 -0.36 0.05
sub-100926 1 1 0.34 -1.14 -1.36 20.05
sub-101028 2 2 19.34 -10.14 -1.36 -6.95
sub-101045 2 2 -8.66 -3.14 -1.36 -9.95
sub-101345 1 1 -0.66 -1.14 -1.36 -7.95
sub-101394 4 2 -12.66 -24.14 -1.36 5.05
...
