Estimating social network size using network scale-up method (NSUM) in Iranshahr, Sistan and Baluchestan Province, Iran.

Background: The network scale-up method is an indirect method of estimating the size of hidden and hard-to-reach populations. An important prerequisite in this method is to estimate the size of an active social network, as considered in the present study. Methods: In 2015, the social network size was calculated using the known subpopulation approach and maximum likelihood estimation in the central, Bampur, and Bazman districts of Iranshahr province. Individuals older than 18 years took part in a streetbased survey. The relationship between the demographic variables and social network size estimation was analyzed (p< 0.05). Linear regression was used to investigate the relationship of each known subpopulation with underlying variables. Data were analyzed in Excel 2010 and SPSS 19. Results: From among 1000 participants, 50.2% lived in rural areas. The social network size of the residents of Iranshahr was estimated to be 308.35 with 12 remaining subgroups. The Pearson's correlation coefficient between the real and estimated values in known subpopulations was equal to 0.92 (p= 0.001). Men aged 25-39 years, those with high education levels, employees, and those residing in villages had a wider social network. The estimated social network size had a significant relationship with gender, education level, and place of residence (p< 0.001). Conclusion: The estimated social network size in Iranshahr was smaller than the value reported by a nationwide study (the ratiobased method).