farid zayeri department of biostatistics, proteomics research center, faculty of paramedical sciences, shahid beheshti university of medical sciences, tehran, ir iran maedeh amini department of biostatistics and epidemiology, school of public health, hamadan university of medical sciences, hamadan, ir iran abbas moghimbeigi department of biostatistics and epidemiology, modeling of noncommunicable disease research center, school of public health, hamadan university of medical sciences, hamadan, ir iran; department of biostatistics and epidemiology, modeling of noncommunicable disease research center, school of public health, hamadan university of medical sciences, hamadan, ir iran. tel: +98-818380398, fax: +98-818380398 ali reza soltanian department of biostatistics and epidemiology, modeling of noncommunicable disease research center, school of public health, hamadan university of medical sciences, hamadan, ir iran nahid kholdi department of health and social medicine, shahed university faculty of medicine, tehran, ir iran mohammad gholami-fesharaki department of biostatistics, faculty of medical sciences, tarbiat modares university, tehran, ir iran