Supplementary Table 1. Variables and corresponding response choices used in the questionnaire and data analyses (Part 1)

Variable / Response choice
Date of birth / (Month) (Year)
Ethnicity / 1) Hans; 2) Others, please specify:
Your highest education level / 1) Illiterate; 2) Primary school (6 years);3) Junior high school (3 years);4) High school, technical or training school(3 years);5) Junior college (2 years);6) College and above
What is your sexual orientation? / 1) Homosexual; 2) Heterosexual;3) Bisexual;4) Not sure;5) Refused to answer
Marriage status / 1) Unmarried; 2) Married; 3) Divorced; 4) Widowed
Have you been diagnosed with the following sexual transmitted diseases？ / 1) None;2) Syphilis; 3) Gonorrhea; 4)Non-gonococcal urethritis; 5)Herpes genitalis; 6) HIVinfection; 7) Anogenital warts; 8) Refused to answer
Have you ever had sex with women? / 1)Yes; 2) No; 3) Refused to answer
How old were you for the first time sex with men？ / At Years old
Do you have fixed homosexual partner currently? / 1) Yes; 2) No
In the past 6 months，How often do you have sex with your sexual partner? / 1) Once a month; 2) 1-3 times per month;3) Once a week; 4) 2-3 times per week;5) >3 times per week
In the past 6 months，how many partners did you have for receptive anal sex? / People
In the past 6 months，how many partners did you have for insertive anal sex? / People

Supplementary Table 1. Variables and corresponding response choices used in the questionnaire and data analyses (Part 2)

Variable / Response choice
Did you use condom during your receptive anal sex? / 1) Always;2) Frequently; 3) Occasionally;4) Never; 5) Refused to answer
Did you use condom during your insertive anal sex? / 1) Always;2) Frequently; 3) Occasionally;4) Never; 5) Refused to answer
In the past year, do you have multiple partner sex with man？ / 1)Yes; 2) No; 3) Refused to answer
In the past year, did you have paid sex with any man？ / 1)Yes; 2) No; 3) Refused to answer
Where and how do you always find sexual partners / 1) Bar; 2) Bath; 3) Park/Public toilet; 4) MSM web; 5) Club; 6) Though friends; 7) Others, please specify: ;8) Refused to answer
The major modes of your homosexual sex / 1) Insertive anal sex; 2) Receptive anal sex; 3) Both insertive and receptive, but be more prone to insertive anal sex; 4) Both insertive and receptive, but be more prone to receptive anal sex; 5) Oral sex; 6) anilinction; 7) SM; 8) Others, please specify:
Is anilinction your regular homosexual behavior? / 1)Yes; 2) No; 3) Refused to answer