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Ahead to Adjustment of 1979-1993 Estimates

Revised NHSDA Methodology in 1994 and 1995

SAMHSA, and previously the National Institute on Drug and Abuse (NIDA), have invested substantial resources over the years to improve and refine the NHSDA in order to enhance accurate measurement of substance use and related problems for use in policymaking. Toward this end, a series of studies was conducted during 1988-1992 to evaluate the survey methodology (Turner, Lessler, and Gfroerer 1992). These studies identified a number of potential improvements to the NHSDA questionnaire. Based on these studies, and consultations with drug survey researchers and data users, an improved instrument was developed, tested, and fielded in 1994. Major improvements in the new questionnaire are:

A new core-supplement structure facilitates the addition or deletion of sets of questions concerning particular policy issues without affecting the measurement of trends in substance use prevalence. This structure also provides for a more consistent measurement of prevalence over time by designating a set of "core" items or questions on the recency and frequency of substance use to be administered the same way every year.

Tobacco questions are asked using a self-administered answer sheet to enhance privacy and improve the reporting of tobacco use, particularly for youths.

Questions are reworded to eliminate vague terms and enhance consistency across different sections of the questionnaire.

A simplified, easier to understand definition of nonmedical use of prescription-type drugs is used.

A calendar is provided during the interview to help the respondent focus on reference periods, improving accuracy when answering recency of drug use questions.

In addition to these questionnaire improvements, new procedures for editing drug use data were implemented in 1994. The new editing procedures use only designated core items to determine substance use prevalence. The consistent use of these editing procedures each year ensures more reliable trend measurement.

When the new questionnaire was introduced in 1994, a supplemental sample was selected for use with the old methodology (i.e., identical to 1993). This provided the capability to assess the impact of the new questionnaire and to measure the effects of the change in methodology. Analyses of the 1994 data have shown that the improvements had a minimal effect on some estimates, but the effect on others was substantial. A separate SAMHSA report provides details on the development of the new questionnaire, editing methods, design of the sample, and the impact of the new methodology on substance use estimates (SAMHSA 1996b). A few key observations from this report are:

Rates of missing data for key drug use variables are lower with the 1994-B (new) questionnaire, indicating improved reliability with the new questionnaire.

The new methodology has a minimal effect on estimates of past month use of most illicit drugs.

Estimates of past year and lifetime use of illicit drugs are slightly lower under the new methodology, primarily because of the revised editing procedures.

Estimates of alcohol use are slightly higher under the new methodology.

Estimates of tobacco use are substantially higher under the new methodology, especially for young people. This is probably due to the use of a self-administered answer sheet for tobacco questions (previously interviewer-administered).

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Ahead to Adjustment of 1979-1993 Estimates

This page was last updated on June 16, 2008.