1 Michel L. A. Dückers, PhD, NIVEL-Netherlands Institute for Health Services Research, Utrecht; and Impact - National Knowledge and Advice Centre for Psychosocial Care Concerning Critical Incidents, Arq Psychotrauma Expert Group, Diemen, The Netherlands. Email: m.duckers@nivel.nl; Eva Alisic, PhD, Monash University Accident Research Centre, Melbourne, Australia; Chris R. Brewin, PhD, Department of Clinical, Educational and Health Psychology, University College London, London, UK.