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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 sameoccasion on at least one day in the past 30 days. Heavy alcohol use isdefined 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 ofdrug, alcohol, and tobacco product use among the American household population age 12 and older. Estimates of drug useprevalence 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 probabilityproportional 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 militarypersonnel on active duty, transient populations (such as homeless people that do not reside in shelters), and residents ofinstitutional group quarters (e.g., jails, hospitals, etc.). Data collection was continuous over the calendar year withapproximately 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 eachresidence, explaining the survey prior to the interviewer's visit. Upon arrival, field representatives conduct a short voluntaryscreening procedure with any resident of the household 18 years of age or older that is capable of providing information onthe age, race/ethnicity, sex, and marital status of each resident 12 years of age or older. This information is used in a randomselection procedure that determines whether any resident members are eligible for an in-depth interview (either one, two, orno individuals are selected). The interviewer has no control over the selection procedure. The 1996 within-householdperson selection probabilities were based on the race/ethnicity of the head of household and the ages of each householdmember. Selected individuals were then asked if they would complete a voluntary interview. NHSDA field representativesconducted the interviews using a paper and pencil questionnaire that included both interviewer-administered questions andself-administered answer sheets (for collection of sensitive information). All screening and interview responses are keptconfidential.
In 1996, a total of 23,240 eligible dwelling unit members were selected for an interview; of these, a total of 18,269interviews 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 designensured adequate sample sizes for four age groups (12 to 17, 18 to 25, 26 to 34, and 35 and older) and three race/ethnicitygroups. 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 ofHispanic origin; and (3) black, not of Hispanic origin. As defined, these groups are mutually exclusive. Those who did notidentify themselves as Hispanic, non-Hispanic white, or non-Hispanic black were included in the category "other." Thisincludes American Indians, Alaska Natives, Pacific Islanders, Asians, and other groups. Separate estimates are not providedfor 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 sincethe 1988 survey. This design uses a composite size measure methodology and a specially designed within-dwelling selectionprocedure to ensure that desired sample sizes would be achieved for subpopulations defined by age and race/ethnicity. Insome survey years, oversampling was used to meet specified precision constraints for these subpopulations. Like the 1993through 1995 NHSDAs, the 1996 NHSDA oversampled Hispanics in areas of high Hispanic concentration to reduce surveycosts. 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 thesample and some individuals living in group quarters (e.g., civilians living on military installations, individuals living incollege 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 uncertaintyor error. The estimates provided are subject to uncertainties of two types: nonsampling and sampling errors. Some sourcesof 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, rigorousattempts were made to minimize their occurrence through pretesting, interviewer training and evaluation, interviewverification, 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 thanconducting a complete census. Different samples drawn using the same procedures from the same population would beexpected 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 confidenceintervals. Asymmetrical 95% confidence intervals were calculated for all estimated proportions and correspondingpopulation estimates. Adjustment procedures for trend data
Beginning in 1994, the NHSDA began using an improved questionnaire and estimation procedure based on a series ofstudies and consultations with drug survey experts and data users. When the new questionnaire was introduced in 1994, asupplemental sample was selected for use with the old methodology (i.e., a questionnaire identical to previous years). Thisprovided the capability to assess the impact of the new questionnaire and to measure the effects of the change inmethodology. Because this new methodology produces estimates that are not directly comparable to previous estimates, the1985-93 NHSDA estimates presented in tables 3.82-3.84 were adjusted to account for the new methodology that was begunin 1994. The substance use prevalence estimates, for nearly all of the substances presented, were adjusted using a simpleratio correction factor. The simple ratio correction factor measured the effect of the new methodology, relative to the oldmethodology, using data from the 1993 and 1994 NHSDAs. For the remaining substances, the prevalence estimates wereadjusted by using a model-based method. Similar to the ratio adjustment, this method of adjusting previous estimates modelsthe 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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