1. Centre for Adolescent Health; Murdoch Children's Research Institute; Royal Children's Hospital; Victoria; Australia
2. Graduate School of Education; University of Melbourne; Victoria; Australia
3. Faculty of Social Sciences; Radboud University; Thomas van Aquinostraat 8, 6525 GD Nijmegen PO Box 9104; 6500 HE; Nijmegen; The Netherlands
4. Medical Research Council; Social and Public Health Sciences Unit; Glascow; UK