Until recently, causal and mechanistic models of ADHD have centered on identifying a single core dysfunction; in other words, many studies are designed with the premise of the existence of an individual major dysfunction. Thus, investigators typically compare a group of children with ADHD defined by core symptoms (e.g. via DSM criteria) to a group of control children without the disorder. Statistical group differences based on psychometrics, functional brain imaging, or genetics are then used to inform causal models of ADHD.
