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1 Nonmedical use; does not include over-the-counter drugs.
2 Binge use is defined as drinking five or more drinks on the same occasion on at least one day in the past 30 days. Heavy alcohol use is defined as drinking five or more drinks on the same occasion on each of five or more days in the past 30 days.
Source: U.S. Substance Abuse and Mental Health Services Administration, National Household Survey on Drug Abuse, annual.
* National Household Survey on Drug Abuse
The National Household Survey on Drug Abuse (NHSDA) is a series of annual national surveys measuring the prevalence of drug, alcohol, and tobacco product use among the American household population age 12 and older. Estimates of drug use prevalence for the civilian, noninstitutionalized population of the United States are presented.
The NHSDA is based on a stratified, multi-stage area probability sample. For 1996, 115 primary sampling units (PSUs) were selected as the first stage of sampling. Within each PSU, area segments were selected with unequal probability proportional to a composite size measure designed to overrepresent concentrated Hispanic and black neighborhoods. Dwelling units were selected from each sample segment. The target population included all civilian residents of households (including civilians residing on military installations) and noninstitutional group quarters (e.g., college dormitories, homeless shelters, rooming houses) 12 years of age and older. Persons excluded from the universe include military personnel on active duty, transient populations (such as homeless people that do not reside in shelters), and residents of institutional group quarters (e.g., jails, hospitals, etc.). Data collection was continuous over the calendar year with approximately one-fourth of the sample allocated to each quarter.
Survey data were collected through personal visits to each selected residence. Introductory letters were mailed to each residence, explaining the survey prior to the interviewer's visit. Upon arrival, field representatives conduct a short voluntary screening procedure with any resident of the household 18 years of age or older that is capable of providing information on the age, race/ethnicity, sex, and marital status of each resident 12 years of age or older. This information is used in a random selection procedure that determines whether any resident members are eligible for an in-depth interview (either one, two, or no individuals are selected). The interviewer has no control over the selection procedure. The 1996 within-household person selection probabilities were based on the race/ethnicity of the head of household and the ages of each household member. Selected individuals were then asked if they would complete a voluntary interview. NHSDA field representatives conducted the interviews using a paper and pencil questionnaire that included both interviewer-administered questions and self-administered answer sheets (for collection of sensitive information). All screening and interview responses are kept confidential.
In 1996, a total of 23,240 eligible dwelling unit members were selected for an interview; of these, a total of 18,269 interviews were completed. Response rates for screening and interviewing were 92.7% and 78.6%, respectively.
Age and race/ethnicity were the two primary correlates of drug use on which the samples were stratified. The sample design ensured adequate sample sizes for four age groups (12 to 17, 18 to 25, 26 to 34, and 35 and older) and three race/ethnicity groups. This oversampling allowed certain subgroups to be large enough to support estimation. Based on the respondents' self-classifications the race/ethnicity groups were classified as: (1) Hispanic in origin, regardless of race; (2) white, not of Hispanic origin; and (3) black, not of Hispanic origin. As defined, these groups are mutually exclusive. Those who did not identify themselves as Hispanic, non-Hispanic white, or non-Hispanic black were included in the category "other." This includes American Indians, Alaska Natives, Pacific Islanders, Asians, and other groups. Separate estimates are not provided for this category because the sample size is too small.
The NHSDA surveys have used basically the same multistage area probability sample design that has been employed since the 1988 survey. This design uses a composite size measure methodology and a specially designed within-dwelling selection procedure to ensure that desired sample sizes would be achieved for subpopulations defined by age and race/ethnicity. In some survey years, oversampling was used to meet specified precision constraints for these subpopulations. Like the 1993 through 1995 NHSDAs, the 1996 NHSDA oversampled Hispanics in areas of high Hispanic concentration to reduce survey costs. Unlike the 1993 through 1995 NHDSAs, the 1996 NHSDA did not oversample cigarette smokers ages 18 to 34.
In addition, beginning in 1991, the survey differs from previous years in two ways: Alaska and Hawaii were included in the sample and some individuals living in group quarters (e.g., civilians living on military installations, individuals living in college dormitories, or individuals living in homeless shelters) were included. Sampling error and confidence intervals
In the National Household Survey on Drug Abuse, as in every sample survey, there is some degree of statistical uncertainty or error. The estimates provided are subject to uncertainties of two types: nonsampling and sampling errors. Some sources of nonsampling error are recording and coding errors, nonresponse, computer processing errors, differences in respondents' interpretations of questions, and purposely false answers. Nonsampling errors cannot be quantified, however, rigorous attempts were made to minimize their occurrence through pretesting, interviewer training and evaluation, interview verification, coder training, coding verification, and other quality control measures.
Sampling errors denote the random fluctuations that occur in estimates when a sample of the population is drawn rather than conducting a complete census. Different samples drawn using the same procedures from the same population would be expected to result in different estimates. Many of these observed estimates would differ to some degree from the "true" population value and these differences are due to sampling error. Sampling errors are quantified by way of confidence intervals. Asymmetrical 95% confidence intervals were calculated for all estimated proportions and corresponding population estimates. Adjustment procedures for trend data
Beginning in 1994, the NHSDA began using an improved questionnaire and estimation procedure based on a series of studies and consultations with drug survey experts and data users. When the new questionnaire was introduced in 1994, a supplemental sample was selected for use with the old methodology (i.e., a questionnaire identical to previous years). This provided the capability to assess the impact of the new questionnaire and to measure the effects of the change in methodology. Because this new methodology produces estimates that are not directly comparable to previous estimates, the 1985-93 NHSDA estimates presented in tables 3.82-3.84 were adjusted to account for the new methodology that was begun in 1994. The substance use prevalence estimates, for nearly all of the substances presented, were adjusted using a simple ratio correction factor. The simple ratio correction factor measured the effect of the new methodology, relative to the old methodology, using data from the 1993 and 1994 NHSDAs. For the remaining substances, the prevalence estimates were adjusted by using a model-based method. Similar to the ratio adjustment, this method of adjusting previous estimates models the combined effect of all measurement error differences between the new and old methodologies.
These tables are based on figures supplied by the United States Census Bureau, U.S. Department of Commerce and are subject to revision by the Census Bureau.
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