Mehdi Naderi1, Siamak Sabour2. 1. Clinical Research Development Centre, Taleghani and Imam Ali Hospital, Kermanshah University of Medical Sciences, Kermanshah, Islamic Republic of Iran. 2. Department of Clinical Epidemiology, School of Health and Safety, Shahid Beheshti University of Medical Sciences, Tehran, Islamic Republic of Iran. Electronic address: s.sabour@sbmu.ac.ir.