Evidence-based Pediatrics and Child Health Second edition Editor in Chief Virginia A Moyer Professor of Pediatrics and Epidemiology Associate Director, Center for Clinical Research and Evidence Based Medicine Department of Pediatrics The University of Texas Houston Health Science Center Houston, Texas, USA Senior Associate Editor Elizabeth J Elliott Associate Professor, Discipline of Paediatrics and Child Health University of Sydney, and Consultant Paediatrician, The Children’s Hospital at Westmead Sydney, Australia Associate Editors Ruth Gilbert Senior Lecturer in Clinical Epidemiology and Honorary Consultant Paediatrician Centre for Evidence-Based Child Health Centre for Paediatric Epidemiology and Statistics Institute of Child Health London, UK Terry Klassen Professor and Chair Department of Pediatrics University of Alberta Edmonton, Alberta, Canada Stuart Logan Professor of Paediatric Epidemiology Director, Institute of Health and Social Care Research Peninsula Medical School St Luke’s Campus Exeter, UK Craig Mellis Professor and Foundation Head of Medicine School of Health Sciences Bond University Gold Coast, Queensland Australia David J Henderson-Smart Director Centre for Perinatal Health Services Research Queen Elizabeth Research Institute University of Sydney Sydney, Australia Katrina Williams Staff Specialist Clinical Epidemiology Unit The Children’s Hospital at Westmead Sydney, Australia