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Summary of NHSDA Methodology

The National Household Survey on Drug Abuse is the primary source of statistical information on the use of illegal drugs by the United States population. Conducted by the Federal Government since 1971, the survey collects data by administering questionnaires to a representative sample of the population at their place of residence. Since October 1, 1992 the survey has been supported and directed by the Substance Abuse and Mental Health Services Administration (SAMHSA).

The survey covers residents of households, noninstitutional group quarters (e.g., shelters, rooming houses, dormitories), and civilians living on military bases. Persons excluded from the universe include the homeless who never use shelters, active military personnel, and residents of institutional group quarters, such as jails and hospitals. Appendix 3 describes surveys that cover populations not included in the NHSDA sampling frame.

The 1995 NHSDA employed a multistage area probability sample of 17,747 persons interviewed from January through December 1995. The screening and interview response rates were 94.2 percent and 80.6 percent, respectively. The sample design incorporated the oversampling of blacks, Hispanics, and young people, to improve the accuracy of estimates for those populations.

The household interview takes about an hour to complete and incorporates procedures designed to maximize honest reporting of illicit drug use (e.g., the use of self-administered answer sheets). Data are collected on the recency and frequency of use of various licit and illicit drugs, opinions about drugs, problems associated with drug use, and drug abuse treatment experience. Also collected are data on demographic characteristics, employment, education, income, health status, mental problems, health insurance, utilization of services, and access to health care.

In some years, other agencies co-sponsor the NHSDA to support the collection of information on special topics. In 1994, the Department of Agriculture funded a supplemental rural sample (SAMHSA 1996a), and the Department of Labor funded a module of questions on workplace issues related to substance abuse.

In 1994, the survey questionnaire and editing procedures underwent major changes that may have affected the reporting of substance use. These changes were implemented to improve the measurement of trends, reduce data processing time, and improve the overall quality of data essential to policymakers at all levels of government. A description of the revised methodology is given in the next section.

Because the new methodology affected the levels of substance use reported by respondents and, therefore, the estimates of prevalence, many previously published estimates for the survey years prior to 1994 are not comparable to the estimates for 1994 and 1995. To account for these methodological effects, an adjustment procedure was developed and applied to data for years prior to 1994 presented in this report.

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