Table 1: Description of Eligible Studies for Meta-Analysis on Population Size of MSM in the U.S. Population

Study Name	Population Surveyed	Sampling Method	Data Collection Period for MSM Behavior	Data Collection Method	Behavioral Recall Period	MSM Questions
General Social Survey (GSS) [15]	National household survey of the general U.S. population of non-institutionalized English-speaking persons aged ≥18 years. Spanish-speaking persons included since 2006.	Probability sample of households in the U.S. One individual in each household completed the survey.	1988–2008 for sex with a male in the past year; 1991-2008 for sex with a male in the past 5 years	Face-to-face, interviewer administered survey (paper in 2000; computer-assisted interview [CAI] since 2002). Self-administered paper questionnaire for sexual behavior.	Past year; past 5 years	Gender of sex partners
National Health and Nutrition Examination Surveys (NHANES) [16]	National household survey of the general U.S. population of non-institutionalized civilians aged ≥12 years. Sexual behavior questions only asked of persons aged 17-59 years.	Complex stratified, multistage cluster sample	1999–2008	Interviewer administered, in person CAI. Computerized self-administered questionnaire for sexual behavior.	Past year; lifetime	Number of male sex partners (past year, ever) where “sex” defined as oral or anal sex
National Household Survey on Drug Abuse (now National Household Survey on Drug Use and Health) [17]	National household survey of the general U.S. population of non-institutionalized civilians aged ≥12 years. Sexual behavior questions asked only of persons aged 18-59 years.	Complex stratified, multistage cluster sample	1996	In person interviewer- administered survey by computer-assisted interview (CAI); audio computer–assisted self–interview (A-CASI) for sexual behavior	Past year	Gender of sex partners
National Health and Social Life Survey (NHSLS) [8, 18]	General U.S. population of English speakers aged 18 - 59 years living in households	Probability sampling	1992	In person interviewer-administered paper survey; self-administered paper questionnaire for sexual behavior	Past year; past 5 years; lifetime (since age 13 years)	Any same-gender sex where sex defined as oral or anal sex
National STD and Behavior Measurement Experiment (NSBME) [14]	National telephone survey of the general U.S. population with a residential phone number and an English-speaking respondent aged 18-45 years.	Telephone survey of a probability sample (list-assisted RDD) of men aged 18-45 residing in U.S. households with a working landline telephone	Sept. 1999 – April 2000	Telephone survey; phone numbers were randomly assigned to the interviewer- administered computer-assisted telephone interview or telephone CASI.	Past year; past 5 years; lifetime	Sex with a man involving genital area/ penis contact
National Survey of Family Growth (NSFG) [9]	National household survey of the general U.S. population aged 15-44 years. Oversampling of teenagers and black and Hispanic adults	A nationally representative multistage area probability sample drawn from 121 areas of the U.S.	Cycle 6: Mar. 2002 – Mar. 2003	In person interviewer administered by CAI; A-CASI for sexual behavior questions.	Past year; lifetime	Same sex sexual contact, where sexual contact defined as oral or anal sex
Project HOPE International Survey of AIDS-Risk Behaviors [13]	General U.S. population of non-institutionalized persons aged 16-50 years. Residents of Alaska and Hawaii were excluded.	Stratified, cluster sample of households in the U.S. (strata were geographic region and metropolitan versus nonmetropol. residence).	1988	In person interviewer administered paper survey; self-administered paper questionnaire for sexual behavior	Past 5 years	Oral or anal sex with a man.