ABSTRACT
The taxonomy and aetiology of childhood psychiatric disorders have been of long-standing interest to researchers, clinicians, teachers, and parents. Accurate classification and a comprehensive understanding of aetiology are prerequisites to effective prevention of these behaviour problems and their sequelae. One factor complicating such an understanding is the considerable overlap among these disorders. A number of studies have documented the overlap among the disruptive behaviour disorders of childhood in both clinical and non-clinical samples. The participants were 3- to 15-year-old male and female same- and opposite-sex twin pairs and their non-twin siblings, aged 3 to 18 years. Twins were recruited from the Australian National Health and Medical Research Council (NHMRC) funded Australian Twin Registry, a nationwide, population-based volunteer registry. Information on zygosity came from the mothers’ responses to 11 questions regarding their twins’ physical similarity.
