Page 84 - Age of onset of disruptive behavior of residentially treated adolescents -Sjoukje de Boer

vocational or junior general secondary education, senior general secondary, or pre- university education).
Disruptive behaviour
Presence of (types of) disruptive behaviour was determined, based on the age when treatment was sought for disruptive behaviour or special education was indicated due to this behaviour, and the age at which the youngster started to commit criminal offences. The disruptive behaviour of the adolescent inpatients that were examined was categorized according to the framework of Frick et al. (1993), and included aggression (i.e., homicide attempt, assault, robbery, physical abuse, sexual offences, threatening someone), oppositional behaviour (i.e., disobedient, doing things their own way, stubbornness), status offences (i.e., running away, truancy, substance usage), and property violations (i.e., selling drugs, lying, possession of weapons, stealing, setting fires, vandalism, fencing stolen goods, traffic offences) (De Boer et al., 2013; De Boer et al., 2012; Frick et al., 1993). The categories of disruptive behaviour were used to compare the subgroups. Also, for each participant the presence and age of onset of disruptive behaviour was determined. Disruptive behaviour was considered present when it was mentioned by at least one of the sources (i.e., file, therapist, or participant), and absent when not present according to all sources. When no information was available, it was coded as unclear (or missing, depending on the reason for unavailability). The earliest age reported by any source was used as the age of onset. Because the course of the adolescent inpatients’ future disruptive behaviour was as yet unknown, the terms early-onset (EO) and adolescent-onset (AO) were used instead of LCP or AL. Participants with disruptive behaviour starting prior to age 12 were considered belonging to the EO group and those whose disruptive behaviour started from age 12 on were labelled AO (De Boer et al., 2013). This was in accordance with Moffitt (1993; Moffitt et al., 1996), and also with Dean (Dean et al., 1996), who found that differences between the EO and AO groups were only evident when the threshold was set to age 12. The distinction in the EO and AO groups was performed by the main researchers. For 195 of the 224 participants the age of onset of disruptive behaviour could be determined (87.1% of the sample), resulting in 139 early-onset (71.3%) and 56 adolescent-onset youths (28.7%). The inter-rater reliability (Cohen’s
82