Drug War Distortions: Drug Use Estimates

Distortion 2: We are winning the ‘drug war.’ Regular drug use has been cut in half since 1979.
It is difficult to measure illicit drug use rates because this is an illegal activity. The government relies on surveys to determine the level of use, and under-reporting is common because illicit drug use is heavily stigmatized in the US.

[National Research Council, "Informing America’s Policy On Illegal Drugs" (Washington, DC: National Academy Press, 2001): "It is widely thought that nonresponse and inaccurate response may cause surveys such as the NHSDA and MTF to underestimate the prevalence of drug use in the surveyed populations (Caspar, 1992)." (p. 93)]

Federal surveys show an increase in use, especially by adolescents, since 1990.

["Monitoring The Future: National Survey Results on Drug Use, 1975-2000, Volume 1: Secondary School Students" (Washington, DC: National Institute on Drug Abuse, 2001), p. 115, and and "Volume II: College Students and Young Adults Ages 19-40," p. 102.]

More reliable data on trends is overdose deaths and emergency room mentions of drugs. These numbers have escalated consistently since the 1980s, and both are at record highs.

[Office of Applied Studies, Substance Abuse and Mental Health Services Administration, US Dept. of Health and Human Services, "Year-End 2000 Emergency Room Data from the Drug Abuse Warning Network (Washington, DC: DHHS, July 2001), p. 2.]

Also, since 1979 the illicit market has created a host of new drugs, most notably crack, in addition to the proliferation of methamphetamine. Even if the survey data relied on were correct, the drug market has gotten more dangerous and drug abuse has become more widespread.

"The years 1978 and 1979 marked the crest of a long and dramatic rise in marijuana use among American high school seniors (and, for that matter, among young people generally). As Tables 5-2 through 5-3 and Figure 5-4a illustrate, annual and 30-day prevalence of marijuana use leveled between 1978 and 1979, following a steady rise in the preceding years. In 1980, both statistics dropped for the first time and continued to decline every year through 1992, except for a brief pause in 1985. Following this twelve-year decline, annual use among twelfth graders began to rise sharply beginning in 1993. In all, it nearly doubled between 1992 and 1997, from 22% to 39%. Thirty-day use also rose significantly, doubling from the 1992 level of 12% to 24% in 1997. It was not until 1998 that these statistics turned around, although neither declined by a significant amount, and neither declined any further in 1999."

Source: Johnston, Lloyd D. PhD, Patrick M. O’Malley, PhD, and Jerald G. Bachman, PhD, Institute for Social Research, "Monitoring The Future: National Survey Results on Drug Use, 1975-2000, Volume 1: Secondary School Students" (Washington, DC: National Institute on Drug Abuse, 2001), p. 115.

"Longer term declines among young adults in the annual prevalence of a number of drugs appeared to end in 1992 (see Table 5-2). Among the 19- to 28-year-old young adult sample this was true for the use of any illicit drug, any illicit drug other than marijuana, marijuana, amphetamines, and crack. In 1993 and 1994, annual prevalence for most drugs remained steady. Cocaine other than crack leveled in 1993 after a period of substantial decline. In 1995, there were modest increases (a percentage point or less) in the annual prevalence of almost all of the drug classes in Table 5-2, some of which were statistically significant. Thus, it is clear that by 1992 the downward secular trend observable in all of these age strata (as well as among adolescents) was over."

Source: Johnston, Lloyd D. PhD, Patrick M. O’Malley, PhD, and Jerald G. Bachman, PhD, Institute for Social Research, "Monitoring The Future: National Survey Results on Drug Use, 1975-2000, Volume II: College Students and Young Adults Ages 19-40" (Washington, DC: National Institute on Drug Abuse, 2001), p. 102.

"From 1990 to 2000, total drug-related episodes increased 62 percent, from 371,208 to 601,776 (Figure 1). Mentions of the four major illicit drugs increased from 1990 to 2000 as follows: marijuana/hashish (514%, from 15,706 to 96,446), heroin/morphine (187%, from 33,884 to 97,287), methamphetamine/speed (158%, from 5,236 to 13,513), and cocaine (118%, from 80,355 to 174,896) (Figure 2)."

Source: Office of Applied Studies, Substance Abuse and Mental Health Services Administration, US Dept. of Health and Human Services, "Year-End 2000 Emergency Room Data from the Drug Abuse Warning Network (Washington, DC: DHHS, July 2001), p. 2.

"Whether the subject of interest is prevalence, frequency, or quantity consumed, questions about the quality of self-reports of drug use are inevitable. The usefulness of the data obtained from a survey is reduced if some sampled individuals fail to answer one or more questions on the survey (nonresponse) or give incorrect answers (inaccurate response). In particular, nonresponse and inaccurate response may lead investigators to draw incorrect conclusions from the data provided by a survey. Response problems occur to some degree in nearly all surveys but are arguably more severe in surveys of illegal activities. For example, some individuals may be reluctant to admit that they engage in illegal behavior, whereas others may brag about such behavior or exaggerate it. It is widely thought that nonresponse and inaccurate response may cause surveys such as the NHSDA and MTF to underestimate the prevalence of drug use in the surveyed populations (Caspar, 1992)." (p. 93)

"Consider, for instance, drawing inferences on the levels and trends in annual prevalence of use rates for adolescents during the 1990s. Data from MTF imply that annual prevalence rates for students in 12th grade increased from 29 percent in 1991 to 42 percent in 1997. Data from the NHSDA indicate that the annual prevalence rates of use for adolescents ages 12 to 17 increased from 13 percent in 1991 to 19 percent in 1997. Both series suggest that from 1991 to 1997, the fraction of teenagers using drugs increased by nearly 50 percent. Does the congruence in the NHSDA and MTF series for adolescents imply that both surveys identify the trends, if not the levels, or does it merely indicate that both surveys are affected by response problems in the same way?" (p. 94)

"Approximately 15 percent of the students surveyed by MTF fail to respond to the questionnaire and approximately 25 percent fail to respond to the NHSDA." (p. 95) (footnote: "The 25 percent nonresponse rate for the NHSDA includes both unit (household) and element (person) nonresponse. The 15 percent nonresponse rate cited for MTF includes student nonresponse only. Schools that refuse to participate in the MTF survey are replaced by similar schools.") (p. 95)

"Caspar (1992) used a shortened questionnaire and monetary incentives to elicit responses from 40 percent of the nonrespondents to the 1990 NHSDA in the Washington, DC area. He found that nonrespondents have higher prevalence rates than do respondents. It is not known whether this finding applies to all nonrespondents or only those who responded to Caspar's survey. Rather than impose the missing-at-random assumption, it might be sensible to assume that the prevalence rate of nonrespondents is no less than the observed rate for respondents. Maintaining this assumption, Pepper obtained bounds on prevalence (Appendix D). The lower bound results if prevalence among nonrespondents equals that among respondents. The upper bound results if all nonrespondents use illegal drugs. True prevalence is within these bounds. Using data from MTF, Pepper found that annual prevalence for 12th graders lies between 29 and 40 percent in 1991 and between 42 and 51 percent in 1997. Thus, the data place prevalence within about a 10 percentage point range." (pp. 96-97)

"A few studies have attempted to evaluate misreporting in broadbased representative samples. However, lacking direct evidence on misreporting in the national probability surveys, these studies make strong, unverifiable assumptions to infer validity rates. Biemer and Witt (1996) analyzed misreporting in the NHSDA under the assumption that smoking tobacco is positively related to illegal drug use and independent of valid reporting. They found false negative rates (that is, the fraction of users who claim to have abstained) in the NHSDA that vary between 0 and 9 percent. Fendrich and Vaughn (1994) evaluated denial rates using panel data on illegal drug use from the National Longitudinal Survey of Youth (NLSY), a nationally representative sample of individuals who were ages 14 to 21 in the base year of 1979. Of the respondents to the 1984 survey who claimed to have ever used cocaine, nearly 20 percent denied use and 40 percent reported less frequent lifetime use in the 1988 follow-up. Of those claiming to have ever used marijuana in 1984, 12 percent later denied use and just over 30 percent report less lifetime use. These logical inconsistencies in the data are informative about validity only under the assumption that the original 1984 responses are correct. Both of these studies require unsubstantiated assumptions to draw conclusions about validity. Arguably, smokers and nonsmokers may have different reactions to stigma and thus may respond differently to questions about illegal behavior. Arguably, the self-reports in the 1984 National Longitudinal Survey of Youth are not all valid. Thus, neither study can be used to draw strong conclusions about validity rates. Still, several broad conclusions about misreporting have been drawn. At the most basic level, there appears to be consistent evidence that some respondents misreport their drug use behavior. More specifically, valid self-reporting of drug use appears to depend on the timing of the event and the social desirability of the drug. Recent use may be subject to higher rates of bias. Misreporting rates may be higher for stigmatized drugs, such as cocaine, than for marijuana. False negative reports seem to increase as drug use becomes increasingly stigmatized. The fraction of false negative reports appears to exceed the fraction of false positive reports, although these differences vary by cohorts. Finally, the validity rates can be affected by the data collection methodology. Surveys that can effectively ensure confidentiality and anonymity and that are conducted in noncoerced settings will tend to have relatively low misreporting rates. Without knowledge of the fraction of respondents who misreport their drug use, it is not possible to identify either prevalence levels or trends. Johnston et al. (1998) argue that invalid reporting rates in the national surveys are low and vary little from year to year so that the data can be used to infer trends. Pepper discusses some potentially plausible assumptions about incorrect response that make it possible to bound prevalence level (Appendix D). It is not known, however, whether either Johnston's or Pepper's assumptions are correct. Concerns about inaccurate response in the NHSDA and MTF are not new." (pp. 99-100)

Distortion 2: Drug Use Estimates