1. Department of Hygiene and Epidemiology, Athens University Medical School, Athens, Greece, , Department of Epidemiology, Harvard School of Public Health, Boston, USA
2. Department of Hygiene and Epidemiology, Athens University Medical School, Athens, Greece
3. Centre for Research and Prevention of Injuries among the Young, Athens University Medical School, Athens, Greece
4. World Health Organisation, Geneva, Switzerland
5. Department of Hygiene and Epidemiology, Athens University Medical School, Athens, Greece, Department of Epidemiology, Harvard School of Public Health, Boston, USA