Page 50 - Age of onset of disruptive behavior of residentially treated adolescents -Sjoukje de Boer

Statistical analysis
All analyses were performed using the Statistical Package for the Social Sciences, version 17.0 (SPSS, 2008). As all of the characteristics were risk indicators for onset of disruptive behavior at a young age, it was expected that they would be more present in the EO group than in the AO group, and we tested one-sided for differences. Although many childhood factors that were associated with LCP antisocial behavior seem to apply to females as well, there are indications that gender differences exist (e.g., Barnes & Beaver, 2010; Eme, 2007; Odgers et al., 2008). For this reason we checked for gender specificity of the characteristics. First, with chi-square tests (categorical variables) or student t-tests (continuous variables), the EO group was compared with the AO group. A level of significance of p<.003 (Bonferroni correction) was chosen to account for the number of characteristics tested. Second, in a logistic regression analysis (dependent EO vs AO), all characteristics were included that differed significantly (p<.05) between EO and AO groups as independent variables, as well as sex. We tested for sex specific characteristics by including interaction terms with sex. Interactions with a p-level of <.10 were included in the model. The Nagelkerke R-square of the model was used as measure for effect size.
Results
Over 20% of the sample had a penal measure and approximately 50% had a civil measure. Some of these individuals had a civil measure and a penal measure. In addition to their psychiatric problems, all patients in the sample displayed severe disruptive behavior.
Table 2 shows the characteristics by EO and AO classification. Males were overrepresented in the EO group (82% vs 18% females) and in the AO group (65% vs 35% females). Table 2 shows that EO and AO groups differed on individual characteristics (in occurrence and age at grade retention in primary school, and in impulsive behavior), family and context characteristics (parental divorce (before child age 11), the number of changes in home environment, and physical abuse), parental characteristics (employment of the mother), and system characteristics (age at first placement outside of the home). The EO and AO groups did not differ on IQ, single
48