[Freesurfer] Contrast for continuous-by-continuous interactions

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Hi experts,

I am using the command line stream on Freesurfer for my analyses. Although I have successfully designed all my contrasts, I wanted confirmation from you regarding one contrast that I am unsure about. Will you please check if the below contrast appropriately investigates age-by-IQ interaction effects across my two groups (TD and NDDs)?

I am also copying here information regarding my regressors and the first few lines of my FSGD file for further detail.

*Contrast:* To examine age-by-IQ interaction effects across groups (TD and NDDs): agexIQinteraction_acrossgroups.mtx

0 0 0 0 0.5 0.5 0.5 0.5 0 0 0 0 -0.5 -0.5 -0.5 -0.5

My regressors:

· 2 discrete factors: Diagnosis, sex

· 4 groups/levels/classes: TD M, TD F, NDD M, NDD F

· 3 continuous covariates: age, SA, IQ

· Number of classes: 4

· Number of variables: 3

· NregressorsDODS= Nclasses*(Nvariables+1)= 4*(3+1)= 16

· Regressor 1: ones for TDM subjects, 0 otherwise. Codes intercept for TDM

· Regressor 2: ones for TDF subjects, 0 otherwise. Codes intercept for TDF

· Regressor 3: ones for NDDM subjects, 0 otherwise. Codes intercept for NDDM

· Regressor 4: ones for NDDF subjects, 0 otherwise. Codes intercept for NDDF

· Regressor 5: age for TDM subjects, 0 otherwise. Codes for TDM

· Regressor 6: age for TDF subjects, 0 otherwise. Codes for TDF

· Regressor 7: age for NDDM subjects, 0 otherwise. Codes for NDDM

· Regressor 8: age for NDDF subjects, 0 otherwise. Codes for NDDF

· Regressor 9: SA for TDM subjects, 0 otherwise. Codes for TDM

· Regressor 10: SA for TDF subjects, 0 otherwise. Codes for TDF

· Regressor 11: SA for NDDM subjects, 0 otherwise. Codes for NDDM

· Regressor 12: SA for NDDF subjects, 0 otherwise. Codes for NDDF

· Regressor 13: IQ for TDM subjects, 0 otherwise. Codes for TDM

· Regressor 14: IQ for TDF subjects, 0 otherwise. Codes for TDF

· Regressor 15: IQ for NDDM subjects, 0 otherwise. Codes for NDDM

· Regressor 16: IQ for NDDF subjects, 0 otherwise. Codes for NDDF

My FSGD file:

GroupDescriptorFile 1

Title TD_vs_NDDs_sex_age_SA_IQ

Class TDM

Class TDF

Class NDDM

Class NDDF

Variables age SA IQ

Input 100092_01 TDM 0.060861784 1.747581397 0.386693428

…

I'd really appreciate your confirmation of my contrast,

Thanks so much,

Avi