Academic journal article Journal of Drug Issues

Understanding the Differences in Youth Drug Prevalence Rates Produced by the MTF, NHSDA, and YRBS Studies

Academic journal article Journal of Drug Issues

Understanding the Differences in Youth Drug Prevalence Rates Produced by the MTF, NHSDA, and YRBS Studies

Article excerpt

This paper explores potential reasons for the differences in drug use prevalence rates among youth generated by three nationally representative surveys: The National Household Survey on Drug Abuse (NHSDA), the Monitoring the Future (MTF) survey, and the Youth Risk Behavioral Survey (YRBS). The MTF and YRBS are the most similar of the surveys, being conducted among students in a classroom using self-administered questionnaires. The NHSDA is conducted in the respondents household, but it has always used self-administered procedures for the drug questions. Nevertheless, the NHSDA generally reports the lowest drug prevalence rates for youth among the three surveys. There are a number of methodological differences across the surveys that cumulatively, probably account for the differences in estimates. Some of the differences appear to be due to telescoping, in that when a calendar was introduced to anchor past 30 day and 12 month time periods in the NHSDA, prevalence rates for illicit drugs were reduced. However, there is substantial similarity in the trends over time among the three surveys, especially for cigarettes, alcohol and cocaine. Many of the estimates generated by the three surveys have overlapping confidence intervals, which suggests the estimates are not statistically significantly different from one another.

The three major epidemiological surveys in the U.S. that measure drug use prevalence and trends among youth are the National Household Survey on Drug Abuse (NHSDA), the Monitoring the Future (MTF) survey, and the Youth Risk Behavior Survey (YRBS). The MTF and YRBS are school surveys, and the NHSDA is a household survey of the U.S. population ages 12 and older. All use self-report methods and employ a multistage cluster probability design to select a representative sample of the population.

The focus of this paper is a comparison of the national level data on the prevalence of drug use among youth generated by the three surveys. Although the foundation of this paper is to explore the reasons for the differences in the estimates, there may be more similarity than the topic suggests. This paper examines prevalence estimates for 4 classes of drugs: alcohol, cigarettes, marijuana, and cocaine. Comparisons between similar ages/grades of youth for past year and past month drug use show parallel trend lines. Considering the number and types of methodological differences across the three studies, perhaps what is more surprising is the similarity in the estimates. Although the YRBS tends to produce the highest prevalence rates, the MTF and YRBS prevalence estimates are similar. There are more substantial differences in the estimates generated by the NHSDA, which are lower for the same age or grade groupings. There appears to be an age effect, in that the differences are largest for the youngest ages/grades. It has customarily been assumed that higher prevalence rates equates with more valid reporting.

The question that is asked of all three surveys, and in fact, all surveys of drug use, is how valid are the results? MTF researchers have done fairly extensive analyses in an effort to determine the reliability and validity of self-reported drug use (O'Malley, Bachman, & Johnston, 1984). High school seniors' reports of friends' use of drugs is highly consistent with self-reported drug use in the aggregate. Reported drug use relates in ways that seem internally consistent (more use among males, among the more delinquent, among the less academically successful, for example), which is a form of construct validity. In the longitudinal data, there is consistency in the self-reported behaviors over a 3-4 year period. There is also a high degree of consistency among logically related measures of drug use within the same questionnaire administration. The principle investigators further point out that at the peak of drug use, two-thirds of the seniors and 80% of the follow-up respondents reported some use of illicit drugs in their lifetime, "which constitute prima facie evidence that the degree of underreporting must be very limited. …

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