Participants and interview procedure

The target population of YARHC survey are unmarried youth aged 15–24 years in mainland China (Tibet, Hong Kong, Macao, and Taiwan were excluded due to geographic, political, economic, and cultural reasons). A total of 579 interviewers were trained using the standard set by the survey expert committee; Before the formal survey, which was conducted between October 20 and November 30 in 2009, preliminary interviews in a pilot study were conducted in May of the same year. Necessary measures including independent environments and anonymity were ensured to protect the privacy of youth, and all respondents were interviewed face-to-face without a third-party present. Sensitive questions related to sexual experience and behaviors in the questionnaire were self-administered and completed by participants themselves. All completed questionnaires were collected in ballot boxes. Additionally, sex was respected in the survey process, with respondents being interviewed by interviewers of the same sex.