Covariates
Scanner: In order to control for variance due to site (for which specific information not available), we included the variable "device serial number" which indicates the individual MR scanners used to acquire data. In this dataset there were 27 separate devices included, however two had no data leaving 25 separate scanners. The number of subjects acquired per scanner varied from a minimum of 9 to a maximum of 283 (see Figure \ref{191427}).