**1. Introduction**

138 Epidemiology Insights

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Epidemiological information is needed for developing public policies to improve children's mental health. In particular, epidemiological research could provide answers to questions such as 1) How many children in the community have mental health problems; 2) What is the distribution of mental health problems across age, sex, levels of socio-economic status, and neighbourhood disadvantage; 3) What is the information about mental health problems from different informants (parents, teachers, and the child); and 4) What is the developmental course of mental health problems in childhood (Costello & Angold, 2006)? Answers to such questions may assist policy-makers and clinicians in designing strategies for improving mental health in children.

After briefly explaining epidemiological concepts and strategies, a selective review of epidemiological research relevant to child mental health policies is given. The purpose of the second part of this chapter is to report on results of two studies. The studies were performed in order to assess the prevalence of emotional and behavioural problems from different informants, to investigate factors which may be associated with prevalence, and to determine the prevalence and incidence rates of ADHD and ODD from preschool to primary school. Of additional concern was the developmental course of externalizing behaviour problems. Finally, the implication of the epidemiological outcomes for future research and mental health services are discussed.
