Introduction - 2000 NHSDA - Substance Dependence, Abuse, and Treatment

This report presents information from the 2000 National Household Survey on Drug Abuse (NHSDA) on national estimates of the extent of substance dependence, abuse, and treatment. It also provides national estimates of what has been called the treatment gap (defined as those persons needing treatment who did not receive treatment in the past year) and of the need for and receipt of treatment for an illicit drug problem. Prior NHSDA reports and special analyses have included estimates of these measures. However, due to significant changes to the NHSDA questionnaire and the definitions and estimation methods used, the estimates of these measures from the 2000 NHSDA are not comparable to prior estimates.

Several important changes to the NHSDA in 1999 and 2000 affected the estimates of drug use, as well as the estimates of dependence, abuse, and needing and receiving treatment. Between 1998 and 1999, the NHSDA switched from a paper-and-pencil-interviewing (PAPI) mode to a computer-assisted interviewing (CAI) mode. All questions on drug use, dependence, and need for treatment no longer were self-administered using a paper-and-pencil interview but rather were administered using audio computer-assisted self-interviewing (ACASI). This methodology allows the respondent to listen to questions through a headset and/or to read the questions on the computer screen. Respondents also key their own answers into the computer. Moreover, major changes were made in the sample design, including an increase in sample size from 20,000 to 72,000 persons and a change from a strictly national design to a State-based sampling plan. For the 2000 survey, revisions were made to the dependence questions that also affected the dependence and treatment need estimates.

Besides the changes to the NHSDA described above, two changes in 2000 had a major impact on the estimates of treatment need and the gap. Treatment need was determined by questions dealing with dependence and abuse. The use of a ratio adjustment to inflate NHSDA estimates was eliminated. A detailed description of these changes and their impact on the estimates can be found in Appendix C.

The definition of treatment need for 2000 classifies a respondent as needing treatment if he or she meets the criteria for dependence or abuse or received treatment at a specialty facility. Dependence or abuse status was determined using the criteria specified in the 4^th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (American Psychiatric Association [APA], 1994). A detailed description of the DSM-IV criteria and the questions that cover them are also given in Appendix C. The questions on dependence ask about health, emotional problems, attempts to cut down on use, tolerance, withdrawal, and other symptoms associated with substances used. The questions on abuse ask about problems at work, home, and school; problems with family or friends; physical danger; and trouble with the law due to the substances used. Dependence reflects a more severe substance abuse problem than abuse, and persons are classified with abuse of a particular substance only if they are not dependent on that substance. For the 1991 to 1999 surveys, a respondent was defined as needing treatment if he or she was dependent on one or more illicit drugs or met one of three conditions based on types of drugs used, their route of administration, and their frequency of use.

This report addresses the rate of abuse, dependence, and treatment in 2000 and provides estimates of the numbers of persons needing and receiving treatment by demographic and geographic subgroups. Because of the volume of information that can now be presented each year from the expanded NHSDA, this initial report presents only national estimates. State-level estimates of dependence and abuse, based on a complex small area estimation (SAE) method, will be described in a separate report that will be released in the summer of 2002.

The NHSDA is the primary source of statistical information on the use of illegal drugs by the U.S. population. Since 1990, the NHSDA has annually surveyed the civilian, noninstitutionalized population of the United States aged 12 or older. Between 1971, the first year of the survey, and 1988, nine NHSDAs were fielded intermittently (i.e., in 1988, 1985, 1982, 1979, 1977, 1976, 1974, 1972, and 1971). 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 RTI in Research Triangle Park, North Carolina. The project is planned and managed by the Office of Applied Studies (OAS). This chapter 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 homeless persons who do not use shelters, active military personnel, and residents of institutional group quarters, such as jails and hospitals. Appendix D describes surveys that cover populations who are not part of the NHSDA sampling frame.

Prior to 1999, the NHSDA was conducted using a paper-and-pencil interviewing (PAPI) methodology, with the interview lasting about an hour. The NHSDA PAPI instrumentation consisted of a questionnaire booklet completed by an interviewer and a set of individual answer sheets completed by a respondent. All substance use questions and other sensitive questions appeared on answer sheets so interviewers were unaware of respondents' answers. Less sensitive questions, such as demographics, occupational status, household size, and composition, were asked aloud by interviewers and recorded in questionnaire booklets.

Since 1999, the NHSDA interview has been carried out using a CAI methodology. The survey uses a combination of "computer-assisted personal interviewing" (CAPI) conducted by an interviewer and "audio computer-assisted self-interviewing" (ACASI). For the most part, questions previously administered by an interviewer are now administered by an interviewer using CAPI. Questions previously administered using answer sheets are now administered using ACASI. The ACASI technique provides respondents with a highly private and confidential means of responding to questions and increases 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, multistage 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 or 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 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 or 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 and 73.9 percent, respectively. See Appendix B for more information on NHSDA response rates.

1.2 Impact of the Changes on the Estimates of Dependence, Abuse, and Treatment

The redesign of the NHSDA has major implications for the estimates produced from the survey, including the estimates of dependence, abuse and treatment, as well as estimates of the treatment need. As expected, the larger sample size and State-based design made it possible to produce estimates for every State and for smaller population subgroups. The precision of the estimates at the national level has 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 are described in another SAMHSA report (Gfroerer, Eyerman, & Chromy, in press).

Additional changes were made to the 2000 NHSDA specifically to improve the estimates of dependence, treatment, and treatment need. The dependence questions were revised so they are better understood by respondents. The treatment need definition was revised so that the measure of treatment need can be based on widely accepted diagnostic criteria. Producing estimates of treatment need and the treatment gap without the inclusion of the ratio adjustment has improved estimates of the gap and treatment need. Because the new numbers no longer depend on external data that are not consistent from year to year, they can be used to produce improved estimates of trends. Also, estimates of treatment need can be used in subgroup analysis that was not possible when the ratio adjustment was included.

This report summarizes the findings of the 2000 NHSDA on substance dependence, abuse, and treatment. Appendices give technical details on the survey methodology, discuss other sources of data, and provide detailed tabulations of estimates. In addition to the bulk of the tables included in this publication (i.e., those in Appendices E and F), a more extensive set of tables, including standard errors, is available.

Tables and text present rates of dependence, abuse, and treatment for illicit drugs and/or alcohol in the past year. Also included is information about the extent to which those in need of treatment for illicit drug use received treatment.

Data are presented for major racial/ethnic groups in several categorizations. Because respondents are allowed to choose more than one racial group, a "more than one race" category is presented that 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 are comprised by the following groups of States:

Tables have been added to describe substance dependence, abuse, treatment, and treatment need based on population density. For this purpose, counties were grouped using the "Rural-Urban Continuum Codes" developed by the U.S. Department of Agriculture (Butler & Beale, 1994). This variable differs from the "population density" measure presented in previous NHSDA reports. Each county is either in a metropolitan statistical area (MSA) or outside an MSA, as defined by the Office of Management and Budget (OMB). 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 fewer than 1 million. Nonmetropolitan areas are areas outside MSAs. For some tables, small metropolitan areas are further classified as having either fewer than or more than 250,000 in 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 subcounty level. "Urbanized" counties have 20,000 or more population in urbanized areas, "less urbanized" counties have at least 2,500 but fewer 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 abuse, dependence, and treatment, regardless of what the underlying reasons for those differences might be.

A report published in September 2001 provides national estimates of rates of use, numbers of users, and other measures related to illicit drugs, alcohol, cigarettes, and other forms of tobacco from the 2000 NHSDA (SAMHSA, 2001a). Additional tabulations from the 2000 NHSDA are available through the Internet (http://www.oas.samhsa.gov), and additional methodological information will be made available electronically and in OAS publications. A report on State-level estimates from the 2000 NHSDA will be published in the summer of 2002. Analytic reports focusing on specific issues or population groups will continue to be produced by SAMHSA. Topics for a few of the reports in progress are as follows:

A complete listing of previously published reports from the NHSDA and other data sources is available from OAS. 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 (SAMHDA) at the University of Michigan (www.icpsr.umich.edu/samhda). Currently, files are available from the 1979 to 1999 NHSDAs. The 2000 public use file will be available in mid-2002.

Chapter 2 offers estimates of the prevalence and patterns of substance dependence and abuse in the Nation. Chapter 3 provides estimates of the prevalence and patterns of the receipt of treatment for problems related to substance use. Chapter 4 discusses the need for and receipt of treatment specifically for problems associated with illicit drug use. Appendix A describes the survey in more detail discussing the sample design, the methodology, and the data processing. Appendix B provides information on the statistical methods and limitations of the data. Appendix C discusses the measurement of dependence, abuse, treatment, and treatment need and describes the changes to these measures in 2000. Appendix D describes other sources of data on substance abuse, dependence, and/or treatment for a substance abuse problem. Appendix E provides sample size and population tables. Appendix F provides tables with estimates of dependence, abuse, treatment, and treatment need.

SAMHSA, an agency in the Department of Health and Human Services, is the Federal Government's lead agency for improving the quality and availability of substance abuse prevention, addiction treatment, and mental health services in the United States.

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1. Introduction