“…One approach has been to define the groups on the basis of whether the first incident of offending occurred before (ES) or after (LS) 18 years of age (Hodgins and Janson, 2002; Laajasalo and Hakkanen, 2005; Pedersen et al, 2010b; Tengström et al, 2001) or whether or not they had a diagnosis of conduct disorder prior to age 15 (Mathieu and Côté, 2009; Sánchez-SanSegundo et al, 2014). A second approach defines ES as those with an age of first arrest or violence which is less than the age onset of their SMI, and vice versa for the LS (Jones et al, 2010; Kooyman et al, 2012; Taylor, 1993; Van Dongen, 2014, 2015). This latter approach is arguably more developmentally meaningful, being sensitive to the interrelationship between the age onset of illness and offending.…”