Longitudinal Analysis Model

[Nathan Petro]

We are investigating the effect of age across 3 visits on MEG brain activity. We are wanting to know the best way to model this effect using the SwE toolbox. We input all brain data (across all participants and 3 visits) in the “scans” box, and indicated each scan as 1, 2, or 3 in the “visits” box. To control for sex, we entered a vector of 1 or 2 to indicate whether each brain data file belonged to a female or male participant. We also input a vector of numbers to indicate each subject – the numbers matched across all 3 visits. Note that not all subjects possess data for all 3 time points.  

We then input covariates for 1) the intercept (a vector of 1s), 2) Visit (a vector of 1, 2, or 3), 3) age (the age of each participant at each scan), and 4) the visit*age interaction term.  

In the covariates section, is it necessary to model “visit” even though we indicate as much in the “visits” input box? 

Would the visit*age interaction term represent the (modeled as: 0 0 0 1) reflect the effect of age across all 3 visits?