en Occupational Health Original Article <p style="text-align: justify;"><span style="font-size:12px;"><span style="font-family:Arial;"><a name="OLE_LINK26"></a><a name="OLE_LINK25"><strong>Background:</strong></a> To manage a problem, knowing the size of the population associated is of great significance. In this study, direct and indirect (network scale-up [NSU]) methods were used to estimate the population size of students of the university of medical sciences with high-risk behaviors in Rafsanjan, Iran. <span dir="RTL"></span><br> <strong>Materials & Methods:</strong> In this cross-sectional study, using stratified random sampling, 440 students were selected and interviewed from the target group by a standard questionnaire, with three social network size estimation, NSU, and direct methods. The frequency approach of the NSU method was used to estimate the size of groups with high-risk behaviors. Correction coefficients were applied to adjust common errors in this method.<span dir="RTL"></span><br> <strong>Results:</strong> Using the maximum likelihood method, the means of social network size (C) for male and female students were 25.71 and 24.45, respectively. Using the NSU method, the prevalence rates of alcohol drinking, extra-marital sexual relationship, and opium use were 26.57%, 15.28%, and 9.69% among male students and 3.13%, 2.89%, and 1.3% among female students, respectively. Using the direct method, the prevalence rates of alcohol drinking, extra-marital sexual relationship, and opium use were 23.2%, 14.3%, and 6.25% among male students and 2.1%, 2.8%, and 0.34% among female students, respectively.<br> <strong>Conclusions:</strong> Our results showed high-risk behaviors to have a relatively high prevalence among students of Rafsanjan University of Medical Sciences (RUMS). These behaviors were more prevalent among males than females. Thus, it seems necessary to plan preventative measures against drug abuse in academic departments.<span dir="RTL"></span></span></span></p> Social Network,High-Risk Behaviors,Students,Alcohol Drinking,Opium,Extramarital Sex Behavior, 239 248 http://johe.rums.ac.ir/browse.php?a_code=A-10-311-1&slc_lang=en&sid=1 Sahar Peykani sahar.peikani@gmail.com 22400319475328460011347 22400319475328460011347 No MSc in Epidemiology, Dept. of Epidemiology and Biostatistics, School of Medicine, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences Ensieh Gheirati nc.gheirati2020@gmail.com 22400319475328460011348 22400319475328460011348 No MSc in Epidemiology Dept. of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Tehran University of Medical Sciences Mohsen Rezaeian moeygmr2@yahoo.co.uk 22400319475328460011349 22400319475328460011349 No Professor, Dept. of Epidemiology and Biostatistics, Occupational Environmental Research Center, School of Medicine, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences Reza Vazirinejad rvazirinejad@yahoo.c 22400319475328460011350 22400319475328460011350 No Professor, Dept. of Epidemiology and Biostatistics, Social Determinants of Health Research Center, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences Hassan Ahmadinia H.ahmadinia@gmail.com 22400319475328460011351 22400319475328460011351 Yes Assistant Prof., Dept. of Epidemiology and Biostatistics, Occupational Environmental Research Center, School of Medicine, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences