S Martins1, I Carvalho2, J V Santos3, R Duarte4. 1. Medical School, Porto University, Portugal. Electronic address: saracfv_21@hotmail.com. 2. Hospital Centre of Vila Nova de Gaia/Espinho, Portugal. 3. Department of Health Information and Decision Science, Faculty of Medicine, University of Porto, Portugal; CINTESIS - Center for Health Technology and Services Research, Portugal. 4. Medical School, Porto University, Portugal; Hospital Centre of Vila Nova de Gaia/Espinho, Portugal; Department of Clinical Epidemiology, Predictive Medicine and Public Health, Medical School, Porto University, Portugal; EPIUnit Institute of Public Health, Porto University, Portugal.