**6.4 Discussion**

In summary, with regard to the empirical approach a considerable variation and a significant increase in the prevalence of externalizing problems were found. The results for preschool aged children correspond with other German findings reported by Beyer and Furniss (2007). Within the BELLA study, a representative national sample of children and adolescents was surveyed (Ravens-Sieberer et al., 2008). Parent's report on externalizing problems in children aged 7-10 indicated a slightly lower prevalence than in the current sample. In a multicultural study on the CBCL, Externalizing scores generally decreased with age (Achenbach & Rescorla, 2007). A review by Rescorla et al. (2007a) included data from 31 societies. Therefore, our findings were unexpected and might be important in understanding mental health in the preschool and primary school years. Discrepancies were attributed to different assessment instruments, sample procedures, use of cut-off points, and normative data. In this study, prevalence rates of 7 - 10% for the diagnoses of ADHD according to DSM-IV symptom criteria were found. When compared with a representative German sample (Döpfner, Breuer, et al., 2008), similarities are seen concerning the prevalence in the age group 7 -10 years. Our prevalence rates are also in line with results found in other countries and cultures and with other assessment instruments. In their international review, Polanczyk et al. (2007) found an overall rate of 5.3 % and a rate of 4.6 %

comparison with rates of ADHD- and ODD-disorders in childhood, the percentage of children in the group "temporary clinical" was relatively high. Regarding the ADHDdisorders and as shown in Figure 3, 83.8 % of our sample was stable normal and showed no clinical relevant ADHD-symptoms over the course. Overall, 12 % of children met at least at one assessment time the criteria for a disorder of ADHD. For 3.7 % of the sample the *stable clinical* pattern was observed. These children met on at least four occasions the criteria for a DSM-IV ADHD disorder. We found similar results in terms of oppositional deviant disorder: Stable normal behaviour was seen in 80.1 % of the sample. The percentage of the *stable clinical* pattern (3.7 %) corresponds with that for the rate of attention deficit-/hyperactivity. Only in relation to the temporary clinical course was a

Developmental pattern CBCL-EXT DSM-IV ADHD DSM-IV ODD Stable normal 61.0 83.8 80.1 Temporary clinical 31.6 12.5 16.2 Stable clinical 7.4 3.7 3.7

Table 2. Developmental course of externalizing problem (CBCL EXT) behaviour and DSM-

In summary, the results showed that about 80 % to 84 % of the preschool children were stable normal with regard to the development of ADHD- and ODD-disorders. However, when only CBCL externalizing scores were taken into consideration the rate decreased from 80 % to 60 %. In about one third of the sample temporary clinical CBCL Externalizing scores were observed. In contrast to results for the diagnostic categories of DSM-IV these rates are two-fold higher. Regarding the stable clinical pattern from preschool to primary school, 4 % of the children fulfilled the criteria for an ADHD- or an

In summary, with regard to the empirical approach a considerable variation and a significant increase in the prevalence of externalizing problems were found. The results for preschool aged children correspond with other German findings reported by Beyer and Furniss (2007). Within the BELLA study, a representative national sample of children and adolescents was surveyed (Ravens-Sieberer et al., 2008). Parent's report on externalizing problems in children aged 7-10 indicated a slightly lower prevalence than in the current sample. In a multicultural study on the CBCL, Externalizing scores generally decreased with age (Achenbach & Rescorla, 2007). A review by Rescorla et al. (2007a) included data from 31 societies. Therefore, our findings were unexpected and might be important in understanding mental health in the preschool and primary school years. Discrepancies were attributed to different assessment instruments, sample procedures, use of cut-off points, and normative data. In this study, prevalence rates of 7 - 10% for the diagnoses of ADHD according to DSM-IV symptom criteria were found. When compared with a representative German sample (Döpfner, Breuer, et al., 2008), similarities are seen concerning the prevalence in the age group 7 -10 years. Our prevalence rates are also in line with results found in other countries and cultures and with other assessment instruments. In their international review, Polanczyk et al. (2007) found an overall rate of 5.3 % and a rate of 4.6 %

slightly higher rate (16.2 % to 12.5 %) observed.

IV-disorders. Data in percent.

ODD-DSM-IV disorder.

**6.4 Discussion** 

for Europe in general. The findings of this study support the assumption that studies without a definition of impairment had significantly higher prevalence rates than those with a definition of impairment. Besides, the diagnostic approach on oppositional defiant disorder in the preschool and primary school years has yielded prevalence rates ranging from 7.4 to 10.5 %. These results are consistent with the lifetime prevalence of ODD reported by Nock et al. (2007), who found a rate of 10.2 %. Prevalence estimates in previous studies have yielded a wide range from 2 - 15% (e.g. Loeber, Burke et al., 2000). Our prevalence is concordant with those of another European study on preschool children. Furthermore, although considerable research exists on ADHD and conduct disorder, information regarding ODD is limited.

So far, no comparable studies reporting incidence rates on externalizing behaviour have been published. In the absence of sufficient comparison studies it is not yet clear whether the findings reported here can be generalized. Further research is urgently called for to answer this important question. Therefore, incidence rates and the developmental course of externalizing problem behaviour are considered together.

On the CBCL about 7 % of preschool and primary school children showed a stable pattern of relevant externalizing problem behaviour. A recent study by van Lier et al. (2007) assessed the trajectories of parent-rated symptoms of conduct problems from age 4 to 18 years old also in a general population sample. In this broader age group slightly lower rates (4 - 5 %) of a high trajectory of ODD- and ADHD-symptoms were found. A thorough statistical analysis of trajectories through growth mixture modelling on a large sample size of Dutch children yielded these results. The discrepancies in findings from those in the present study were attributable to different age groups, data collection and recruitment procedures, and CBCL-versions. The results on the stable normal pattern are in line with data from the literature (Bongers et al., 2003; Keiley et al., 2000).

The study had several strengths. First, it is one of the rare studies with preschool children conducted in a universal setting with a 4-year follow-up over that time span. Second, the time intervals between the assessments were shorter compared with other longitudinal studies examining the same topic. Third, we used two different diagnostic approaches to describe externalizing problems: one of the best-studied instruments for the evaluation of children´s psychopathology (Achenbach, 2009) and DSM-IV ADHD- and ODD-diagnostic criteria. In this context, the study met for the most part the methodological criteria previously suggested by Robins and Rutter (1990), since it investigated behavioural problems in a sample of the population assessed longitudinally through standardized procedures. The present study is not without limitations. A main limitation is the generalizability of findings. Our sample is relatively advantaged with only 1/3 of all potentially eligible families participating. This finding corresponds to the fact that the rates of families and children recruited for family-focused preventions are typically very low (e.g. Spoth & Redmond, 2000). When interpreting the results, it should be taken into account that the child mental health status was assessed by symptom checklist questionnaires and disorder rating scales. The use of maternal self-report on child behaviour ratings may have been affected by the mother's experience of stress, depressive symptomatology, or marital problems. Given a large number of subjects, the questionnaire approach is economical and offers useful information, but lacks the specificity and additional depth that structured psychiatric interviews might provide.

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Furthermore, a teacher perspective could add valuable information about problem behaviour at school, which might possibly result in reports of more externalizing problems. Due to principles of data collection, frequent change of teachers, and the transition from kindergarten to primary school it was only possible to obtain the parental report. For international comparison of the results, the age at school entry in Germany, generally at the age of 6 years, needs to be taken into account.

To sum up, the study contributes to a more complete understanding of externalizing behaviour problems and their continuity from kindergarten to primary school. The results point to the need for early child psychiatric research on child mental health beginning in infancy and the preschool years. The development of problem behaviour in specific clinical or risk groups may differ from the pattern found in the present data. An increased utilization of child mental health services by older children, who already show disturbances in the preschool years, has important implications for early preschool recognition of child mental health problems and indicates the need for the prevention and development of a differentiated delivery of child mental health services. Clinicians working in primary care, day care, or school systems need to be attentive to opportunities for early detection and intervention regarding preschoolers' externalizing behavioural problems, particularly since efficacious prevention and treatment exists for the psychopathology of young children (e.g. Weisz et al., 2005).
