Sociodemographic Characteristics
All background characteristics of alters were collected in the baseline questionnaire.Sociodemographic characteristics collected include age, marital status, local residence, length of stay in Guangzhou, education, and income. Participants were asked about MSM-related characteristics, including sex orientation, sex role, and whether to recruit male sex partners on the internet. We dichotomized age by 25 years and income by 5000 RMB (US $700) according to the median.