Hi Alfonso and CONN forum members:

I am having some conceptual issues with setting up my second-level analyses, and I'm hoping to receive your advice as to what the best setup would be.
If you don't mind considering my issue, I will first explain my dataset, my setup, and then my questions.

Dataset: Resting-state data of a sample (N=150) with an autism group (ASD), control group (TYP), and a personality behavioral measure (e.g., Neuroticism scored from 1 - 50). I am looking to identify significant associations between Neuroticism scores and ROI-ROI connections in the ASD group (followed by the same analysis for the TYP group afterwards).

Setup:

• AllSubjects = [1 for all 150 participants]; total of 150 values
• ASD = [1 for all 73 participants in the ASD group, 0 for all non-ASD participants]; total of 150 values
• TYP = [1 for all 77 participants in the TYP group, 0 for all non-TYP participants]; total of 150 values
• N_ASD = [Neuroticism values for all ASD participants, 0 for all non-ASD], e.g., [0 0 35 0 42 ...]; total of 150 values
• N_TYP = [Neuroticism values for all TYP participants, 0 for all non-TYP], e.g., [25 20 0 18 0 ...]; total of 150 values
• QC_MeanMotion = [mean motion values for all 150 participants]; total of 150 values

Questions:

• If I wanted to evaluate significant associations of Neuroticism with ROI-ROI connection in the ASD group only (i.e., a regression analysis for a single group), would it make more sense to have a setup of [AllSubjects 0 N_ASD 1] or [ASD 0 N_ASD 1]? Mathematically, they seem equivalent to me since N_ASD provides "0"s for the TYP group anyways, but I'm not completely sure what the difference is. There are other combinations that might make sense (for example, if I collapsed N_TYP and N_ASD into a single Neuroticism covariate with a value for each participant, I could potentially run [ASD 0 Neuroticism 1]?), but again, this is my main conceptual issue with the setup.
• To further consider this example, if I wanted to control for mean motion, I would add in the covariate, e.g., [AllSubjects/ASD 0 N_ASD 1 QC_MeanMotion 0]. However, should the QC_MeanMotion be separated into a QC_MeanMotion_ASD and a QC_MeanMotion_TYP, in which I would use QC_MeanMotion_ASD (a covariate that has "0"s for all TYP participants)?

Thank you very much for taking the time to consider my issue, I look forward to people's thoughts.

Billy