Erfan Ayubi1, Saeid Safiri2. 1. 1Department of Epidemiology,School of Public Health,Shahid Beheshti University of Medical Sciences,Tehran,Iran. 2. 2Managerial Epidemiology Research Center,Department of Public Health,School of Nursing and Midwifery,Maragheh University of Medical Sciences,Maragheh,Iran.