Chapter 1. Introduction
This report presents information from the 2000 National Household Survey on Drug Abuse (NHSDA) on rates of use, numbers of users, and other measures related to illicit drugs, alcohol, cigarettes, and other forms of tobacco. The NHSDA is an annual survey of the civilian noninstitutionalized population of the United States, 12 years old or older.
In 1999, the NHSDA underwent a major redesign. The method of data collection was changed from a paper questionnaire administration to a computer-assisted administration. In addition, the sample design was changed from a strictly national design to a state-based sampling plan. These important changes to the NHSDA have a major impact on the data that are produced from the survey. The expanded sample makes it possible to produce, each year, substance use prevalence estimates for every state and the District of Columbia. It also allows more detailed analyses of national patterns of use. However, because of the differences in methodology and impact of the new design on data collection, only limited comparisons can be made between data from the redesigned surveys (1999 onward) and data obtained from surveys prior to 1999. Therefore, this report addresses primarily the changes in rates of use between 1999 and 2000 and the differences in patterns of use among various demographic and geographic subgroups of the U.S. population.
Because of the volume of information that can now be presented each year from the expanded NHSDA, this initial report on the 2000 data presents only national estimates. State-level estimates, which are based on a complex small area estimation method, will be presented in a separate report which will be released in the fall.
1.1. Summary of NHSDA Methodology
The NHSDA 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 through face-to-face interviews at their place of residence. The survey is sponsored by the Substance Abuse and Mental Health Services Administration (SAMHSA), and data collection is carried out by Research Triangle Institute. The project is planned and managed by the Office of Applied Studies. This section contains a brief description of the survey methodology. A more complete description is provided in Appendix A.
The NHSDA collects information from residents of households, noninstitutional group quarters (e.g., shelters, rooming houses, dormitories), and civilians living on military bases. Persons excluded from the survey include the homeless who do not use shelters, active military personnel, and residents of institutional group quarters, such as jails and hospitals. Appendix C describes surveys that cover populations that are not part of the NHSDA sampling frame.
Prior to 1999, the NHSDA was conducted as a paper-and-pencil interview (PAPI) lasting about an hour. The NHSDA PAPI instrumentation consisted of a questionnaire booklet that was completed by the interviewer and a set of individual answer sheets that were completed by the respondent. All substance use questions and other sensitive questions appeared on the answer sheets so that the interviewer was not aware of the respondent's answers. Less sensitive questions such as demographics, occupational status, household size and composition were asked aloud by the interviewer and recorded in the questionnaire booklet.
Beginning in 1999 the NHSDA interview has been carried out by computer-assisted interview (CAI). The survey uses a combination of computer-assisted personal interview (CAPI) conducted by the interviewer and an audio computer-assisted self-interview (ACASI). For the most part, questions previously administered by the interviewer are now administered by the interviewer using CAPI. Questions previously administered using answer sheets are now administered using ACASI. Use of ACASI is designed to provide the respondent with a highly private and confidential means of responding to questions and to increase the level of honest reporting of illicit drug use and other sensitive behaviors.
Consistent with the 1999 NHSDA, the 2000 NHSDA sample employed a 50-state design with an independent, multi-stage area probability sample for each of the 50 States and the District of Columbia. The eight states with the largest population (which together account for 48 percent of the total U.S. population aged 12 and older) were designated as large sample states (California, Florida, Illinois, Michigan, New York, Ohio, Pennsylvania and Texas). For these states, the design provided a sample large enough to support direct state estimates. For the remaining 42 states and the District of Columbia, smaller, but adequate, samples were selected to support state estimates using small area estimation (SAE) techniques. The design also oversampled youths and young adults, so that each state's sample was approximately equally distributed among three major age groups: 12 to 17 years, 18 to 25 years, and 26 years and older. To enhance the precision of trend measurement, half of the first-stage sampling units (area segments) in the 1999 sample were also in the 2000 sample. However, all of the households included in the 2000 sample were new.
Nationally, 169,769 addresses were screened for the 2000 survey and 71,764 persons were interviewed within the screened addresses. The survey was conducted from January through December, 2000. Weighted response rates for household screening and for interviewing were 92.8 percent and 73.9 percent, respectively. See Appendix B for more information on NHSDA response rates.
1.2. Impact of 1999 NHSDA Redesign on Estimates
The redesign of the NHSDA has major implications for the estimates produced from the survey. While many of the effects had been anticipated, some were not. As expected, the larger sample size and state-based design have made it possible to produce estimates for every state and for smaller population subgroups. The precision of the estimates at the national level is improved substantially. The CAI methodology has made data collection and processing more efficient, and improved the quality of the data. New procedures for editing and imputing the data were implemented in conjunction with the new CAI instrument. In-depth analyses of methodological issues associated with the implementation of the new design have been done and are described in another SAMHSA report (Gfroerer, Eyerman, and Chromy, 2001).
While the redesign improved the NHSDA estimates of substance use prevalence, it also made it difficult to assess long-term trends. Because of the major differences between the CAI and PAPI methods, it is not appropriate to compare the 1999 or 2000 CAI estimates of substance use prevalence to earlier NHSDA estimates to assess changes over time in substance use. In this report, discussion of long term trends is limited to a few key measures and is based on separate analyses of trends from the PAPI data and the CAI data (see Chapter 7).
1.3. Revision of 1999 Estimates
During the processing of the 2000 NHSDA data, an error was detected in the computer programs that assigned imputed values for substance use variables that had missing information in the 1999 NHSDA data file. These variables are used in making estimates of substance use incidence and prevalence. In preparing this report, the 1999 data were adjusted to correct for this error. For most substance use measures, the impact of the revision is small. Estimates of lifetime use of substances were not affected at all. Estimates of past year and past month use were all revised, but the updated numbers in many cases are nearly identical to the previous ones. The effects of the error are noticeable for only four substances (alcohol, marijuana, inhalants, and heroin), in addition to the composite measures "any illicit drug" and "any illicit drug other than marijuana." For these substances, all of the revised estimates are lower than the previous ones. For inhalants, the revised estimates are considerably lower.
The tables included in this report, along with the more extensive set of supplemental 2000 NHSDA tables available from SAMHSA, contain virtually all of the revised 1999 national estimates that correspond to the estimates released in August 2000. Data on SAMHSA's website will now reflect the revised estimates.
1.4. Format of Report and Explanation of Tables
This report includes separate chapters that summarize the findings of the 2000 NHSDA on five topics: use of illicit drugs; use of alcohol; use of tobacco products; initiation of substance use; and prevention-related issues. A final chapter summarizes the results and discusses key findings in relation to other research and survey results. Appendices give technical details on the survey methodology, discuss other sources of data, and provide references and detailed tabulations of estimates. In addition to the tables included in this publication (Appendix E and F), a more extensive set of tables, including standard errors, has been prepared and is available upon request. These tables will also be made available through the Internet.
Tables and text present prevalence measures for the population in terms of both the number of substance users and the rate of substance use for illicit drugs, alcohol, and tobacco products. Tables show estimates of drug use prevalence in the lifetime (i.e., ever used), past year, and past month. The analysis focuses primarily on past month use, which is also referred to as "current use." Most tables present estimates for 1999 and 2000, with an indication of the statistical significance of changes.
Data are presented for major racial/ethnic groups in several categorizations, based on the level of detail the sample will allow. Since respondents were allowed to choose more than one racial group, a "more than one race" category is presented which includes persons who report more than one category among the seven basic groups listed in the survey question (white; black/African American; American Indian or Alaska Native; Native Hawaiian; Other Pacific Islander; Asian; Other). It should be noted that the category "white" shown in this report includes only non-Hispanic whites, the category "black" includes only non-Hispanic blacks, and the category "Hispanic" includes Hispanics of any race. Also, more detailed categories are obtained in the survey for respondents who report Asian race or Hispanic ethnicity.
Data are also presented for four U.S. geographic regions and nine geographic divisions within these regions. These regions and divisions include the following groups of States:
Northeast Region - New England Division: Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut; Middle Atlantic Division: New York, New Jersey, Pennsylvania.
Midwest Region - East North Central Division: Wisconsin, Illinois, Michigan, Indiana, Ohio; West North Central Division: North Dakota, South Dakota, Nebraska, Kansas, Minnesota, Iowa, Missouri.
South Region - South Atlantic Division: West Virginia, Virginia, Maryland, Delaware, District of Columbia, North Carolina, South Carolina, Georgia, Florida; East South Central Division: Mississippi, Tennessee, Kentucky, Alabama; West South Central Division: Texas, Oklahoma, Arkansas, Louisiana.
West Region - Mountain Division: Idaho, Nevada, Arizona, New Mexico, Utah, Colorado, Wyoming, Montana; Pacific Division: California, Oregon, Washington, Hawaii, Alaska.
Tables have been added to describe substance use based on population density. For this purpose, counties are grouped based on the "Rural-Urban Continuum Codes" developed by the U.S. Department of Agriculture (Butler and Beale 1994). This variable differs from the "Population Density" measure presented in previous reports. Each county is either in a Metropolitan Statistical Area (MSA) or outside of an MSA, as defined by the Office of Management and Budget. For counties in New England, New England County Metropolitan Areas (NECMA) are used for defining codes. Large metropolitan areas have a population of 1 million or more. Small metropolitan areas have a population of less than 1 million. Nonmetropolitan areas are areas outside of MSAs. For some tables, small metropolitan areas are further classified as having either less than or greater than 250,000 population. Counties in nonmetropolitan areas are classified based on the number of people in the county who live in an urbanized area, as defined by the Census Bureau at the sub-county level. "Urbanized" counties have 20,000 or more population in urbanized areas, "Less Urbanized" counties have at least 2,500 but less than 20,000 population in urbanized areas, and "Completely Rural" counties have fewer than 2,500 population in urbanized areas.
Other than presenting results by age group and other basic demographic characteristics, no attempt is made in this report to control for potentially confounding factors that might help explain the observed differences. This point is particularly salient with respect to race/ethnicity, which tends to be highly associated with socioeconomic characteristics. The cross-sectional nature of the data limits the capability to infer causal relationships. Nevertheless, the data presented in this report are useful for indicating demographic subgroups with relatively high (or low) rates of substance use, regardless of what the underlying reasons for those differences might be.
1.5. Other NHSDA Reports
Additional tabulations from the 2000 NHSDA have been generated and are available through the Internet. Additional methodological information will also be made available electronically (http://www.oas.samhsa.gov), as well as in OAS publications. A report on state-level estimates from the 2000 NHSDA will be published in the fall. Analytic reports focusing on specific issues or population groups will continue to be produced by SAMHSA. A few of the reports in progress are:
Tobacco Use in America
Substance Dependence, Abuse, and Treatment
Underage Alcohol Use
Characteristics of Recent Marijuana Initiates
Risk and Protective Factors for Substance Use
Characteristics of Adults Using Mental Health Services
A complete listing of previously published reports from the NHSDA and other data sources is available from the Office of Applied Studies. Many of these reports are also available through the Internet (http://www.oas.samhsa.gov). In addition, OAS makes public use data files available to researchers through the Substance Abuse and Mental Health Data Archive (www.icpsr.umich.edu/samhda/). Currently, files are available from the 1979-1998 NHSDAs. The 1999 public use file will be available within the next few months and the 2000 public use file will be available in early 2002.
This page was last updated on June 03, 2008.