The general population component of the HIV behavioral surveillance program includes data from several systems. The Division of HIV/AIDS Prevention (DHAP) at CDC works in partnership with various organizations that conduct ongoing, systematic behavioral surveys to collect, analyze, and disseminate general population HIV behavioral surveillance data. There are several reasons for relying on partnerships to collect general population HIV-related data. One is cost-effectiveness. In addition, the different purposes of each survey (none of which is specific to HIV) means that no single existing data system is able to (1) reach an appropriate sample at the national, state, or local level, (2) employ the best mode of survey administration given the nature of the questions asked, (3) collect data with sufficient frequency, or (4) meet the HIV behavioral surveillance data needs described in this article.
Population-based surveys are expensive, time-consuming, and complex. Therefore, it is not cost-effective to run a general population survey that only meets the needs of HIV behavioral surveillance. The complex sampling designs require skilled staff for planning and implementing the survey as well as for analyzing the data.
The sampling frames for population-based health surveys in the United States differ. Some are nationally representative while others are state-based, and some restrict their samples or HIV-related question sets to individuals of a certain gender or age range.
Different modes of data collection are used, including face-to-face, telephone, self-administered, or some combination of these methods. Mode of administration can affect the responses participants give, particularly to sensitive questions such as sexual behavior and drug use. Each mode of data collection has its advantages and disadvantages; having multiple data sources to compare on similar measures allows for a better estimation of bias from any particular mode of administration or sampling frame.
In terms of frequency of data collection, to be used as part of a surveillance approach, the surveys must be ongoing and systematic. Some systems have periodic data collection and others are continuous.
Because the HIV epidemic in the United States is concentrated (i.e., not widespread in the general population), a limited amount of information is needed from the general population for the purposes of HIV behavioral surveillance. Measurement of behaviors and data analysis for the purpose of HIV behavioral surveillance should be focused on the measures listed in the . These indicators were chosen based on the model for HIV behavioral surveillance2
and reflect common routes of HIV transmission (sexual behavior, injection drug use) and common, widespread prevention strategies in the U.S.
Relevant measures for HIV behavioral surveillance in the U.S. general population
Given the limited scope of data needed for the purposes of general population HIV behavioral surveillance, developing and maintaining partnerships between DHAP at CDC and organizations that conduct population-based surveys is a more efficient strategy than fielding a new surveillance system. The addition of a few key HIV-related questions to various population-based surveys—such as the Behavioral Risk Factor Surveillance System (BRFSS), the National Survey of Family Growth (NSFG), and the General Social Survey (GSS)—provides a sufficient picture of the behaviors driving the epidemic in the general population.
To illustrate the manner in which general population HIV behavioral surveillance is implemented via partnerships with other behavioral data systems, there are three surveys that are part of the HIV behavioral surveillance program: NSFG, GSS, and BRFSS. Although these three surveys were chosen to demonstrate the diversity in the purpose of the surveys and the types of partnerships with DHAP, they are not the only systems that collect HIV-related data from ongoing or repeated population-based surveys.
NSFG and BRFSS are CDC-run surveys, administered by the National Center for Health Statistics (NCHS) and the National Center for Chronic Disease Prevention and Health Promotion (NCCDPHP); information about these surveys can be found at www.cdc.gov/nchs/nsfg.htm
. GSS is administered by the National Opinion Research Center (NORC) at the University of Chicago (http://www.norc.uchicago.edu/projects/gensoc1.asp
). The summarizes the key features of each survey. For all three surveys, as part of the partnership, staff at DHAP provide subject-matter expertise in the development of HIV-related survey questions; data analysis is a collaborative effort among staff from each system and DHAP.
Characteristics of three general population surveys included in CDC's HIV behavioral surveillance program
National Survey of Family Growth (NSFG).
NSFG is a periodic survey of a nationally representative sample of people aged 15–44 and examines factors that affect the formation, growth, and dissolution of families, such as marriage, divorce, births, sexual activity, and contraceptive use.10
NSFG supplements the birth registration system by providing data on behaviors that explain birth and pregnancy rates, as well as serving the needs of other federal programs by including additional demographic and epidemiologic topics. To date, NSFG has been conducted six times: in 1973, 1976, 1982, 1988, 1995, and 2002. Its scope and methods have changed somewhat over time; for example, men were included for the first time in 2002.
In 2002, about 12,600 men and women completed NSFG, and a nationally representative multistage area probability sampling method was used. Trained female interviewers visited the homes of selected people in 120 areas across the country and surveyed one person from each selected household. Interviewers used computer-assisted personal interviewing (CAPI), although parts of the survey—including questions related to HIV risk behaviors—were administered by audio computer-assisted self-interview (ACASI). Data were weighted to produce national estimates.
DHAP contributes funding for questionnaire item development and data collection for NSFG and provides input on decision-making with regard to the survey's design and schedule. DHAP representatives are invited to periodic and ad hoc workshops on NSFG held by the NCHS.
In 1995 and 2002, NSFG questionnaires included a section on sexually transmitted disease (STD)/HIV risk behaviors. This section included questions for women on having male sex partners who had sex with other men and, for men, questions on having male sex partners. Both men and women were asked about number of sex partners, condom use, and injection drug use. The survey also included questions about HIV counseling and testing experiences. With its reproductive health focus, NSFG included a wide range of questions on sexual activity, such as age at first sex and nonvoluntary sex that can be analyzed in the context of HIV risk.
Behavioral Risk Factor Surveillance System (BRFSS).
BRFSS is a system of state-based health surveys that focus on health risk behaviors, clinical preventive health practices, and health care access.11
BRFSS methods allow for annual estimates at both the state and national levels; the indicators of health included in BRFSS are used to measure progress toward disease prevention goals established by the federal government. Approximately 200,000 interviews with adults (aged 18 and older) are conducted each year in all 50 states, the District of Columbia, Puerto Rico, the Virgin Islands, and Guam.
The BRFSS sampling method is a disproportionate stratified sample of telephone numbers in each state. States stratify the sampling frame for high and low household density groups and a probability sample of all households with telephones is obtained in each strata. One person per household is selected to participate. CATI is used to administer the survey, which takes about 20 minutes. Data are weighted for probability of selection of telephone number, the number of adults in a household, and the number of telephones in a household. Post-stratification adjustments are created for nonresponse and households without telephones.
The BRFSS survey is comprised of three components: the core questionnaire, optional modules, and local questions. The core questionnaire is developed each year with input from the states and representatives from the federal government, including DHAP. While BRFSS is primarily focused on risks for chronic diseases, HIV-related questions have been included since the late 1980s. The DHAP representative is responsible for attending BRFSS national meetings and for proposing questions for emerging issues that could impact the HIV epidemic. Efforts are made to ensure the consistency of questions from year to year and to use questions that have been used on other national surveys. Each new question proposed to BRFSS is evaluated through cognitive and field testing before it is added to the questionnaire.
The HIV/AIDS section of the current BRFSS core questionnaire collects the following information: whether the respondent was ever tested for HIV and, if so, the month and year of last test and the facility where last tested; and a general risk variable in which risk behaviors are measured in a single question: respondents only answer “yes” or “no,” but do not indicate a specific risk. In 1997, funding was provided for a sexual behavior module that was used by 23 states, the District of Columbia, and Puerto Rico. In subsequent years, the number of states using this module declined, making multistate analyses difficult and less meaningful. Historically, the HIV/AIDS section of BRFSS has included questions about knowledge and attitudes about HIV and HIV prevention strategies.12
General Social Survey (GSS).
GSS collects information from the general public on a variety of subjects, including attitudes toward social issues, education, religion, government, and other institutions; jobs and the economy; and politics and policy issues. Since 1988, GSS has also collected data on sexual behaviors, including number of sex partners, frequency of intercourse, extramarital relationships, and sex with prostitutes.
GSS, conducted by NORC, was conducted annually for most years between 1972 and 1994, and biennially thereafter. GSS is a national probability sample of all noninstitutionalized English-speaking people 18 years of age or older living in the United States. The interview is conducted in person; starting in 2002, interviewers conducted the survey by using CAPI.
The questionnaire contains a standard core of demographic and attitudinal variables, plus certain topics of special interest selected for rotation (called “topical modules”). The exact wording of questions is retained over time to facilitate trend analyses as well as replications of earlier findings.
The interview takes approximately 90 minutes. In 1994, GSS implemented a split-sample design. The sample consists of two parallel subsamples of approximately 1,500 people each. The two subsamples are administered the identical core questions but differ in the topical modules included. Thus, sample sizes for questions in specific topic modules will be about half the size of the total sample. In 2002, the total sample size was 2,765.
Since 1988, HIV/AIDS-related items have been included on GSS. Currently, these include: number and gender of sex partners, sex with risky partners, condom use at last sex by type of partner (steady or not), injection drug use, and use of crack cocaine. CDC has supported the collection and analysis of these data through a series of contracts with NORC. CDC's current contract with NORC includes the addition of three questions to GSS that measure history of HIV testing for the 2006 GSS.
System strengths and weaknesses
These general population data systems have individual strengths and weaknesses that must be considered for data to be included in a behavioral surveillance program. As previously noted, key features include the purpose of the data system, sampling frames, mode of administration, and frequency of data collection.
A major strength of BRFSS is that it produces state-based and national estimates. For more recent years, city-based estimates are also produced. The utility of state- and local-level data makes this system a recommended part of the HIV epidemiologic profiles that are used to obtain and allocate funds for HIV prevention.13
HIV-related questions on each of the three survey instruments vary in number and topic, based on the purpose of the systems. NSFG and GSS collect data for the indicators in the for sexual behavior, injection drug use, and HIV testing. The BRFSS questionnaire includes each of the HIV testing measures noted in the . Risk behaviors are measured using the single question previously described.
While BRFSS administers the survey by telephone, NSFG and GSS are household-based, face-to-face surveys. Recent response rates in these surveys reflect the current difficulties in conducting telephone surveys: response rates for NSFG (79%) and GSS (70% to 75%) are considerably higher than BRFSS (median response rate in 2000 was 48.9%). Several studies indicate more risk behaviors are reported using ACASI;14, 15
therefore, NSFG may have more reliable sexual behavior data than the other surveys.
GSS has produced a national sample every two years, and BRFSS produces state and national estimates annually; these data systems provide consistent and comparable sources of data to assess changes in HIV-related behaviors over time. NSFG traditionally has been fielded on a periodic basis; the utility of NSFG data for HIV behavioral surveillance has increased with the addition of men to the sample, and plans to begin continuous data collection in 2007 will increase it further.