trends over time and space, and its potential responsiveness to various policy initiatives.

Distribution of Drug Use and Its Consequences

Researchers have devoted considerable attention to the aggregate distribution of alcohol consumption and its changes over time and across settings and modalities of use (see Edwards et al., 1994; Skog, 1993). Like many human attributes, the frequency distribution of alcohol consumption has an asymmetric, positively skewed shape. This asymmetry partly reflects the fact that consumption is bounded on one end at zero, but only fuzzily bounded at the high end by human biological constraints. It may also reflect multiplicative relationships among the causes of consumption and, conceivably, the nature of addiction (c.f., Skog, in Edwards et al., 1994). There is good reason to expect a similar distributional form for many if not all of the illegal psychoactive drugs (Everingham and Rydell, 1994).

Whatever its causes, this skewed distribution may have important consequences for drug policy analysis and intervention. First, it implies that the harmful consequences of drug use are not evenly distributed across all users. Many harms are disproportionately concentrated among heavy users—sharing of infected needles, unsafe sexual behavior, and income-generating violent crime.

These observations enable better understanding of drug use and its consequences. Everingham and Rydell (1994) used an analysis of the statistical distribution of cocaine consumption in an attempt to understand two seemingly contradictory patterns in the early 1990s. On one hand, there was a fairly dramatic decline in the prevalence of cocaine use (i.e., the number of users) between 1983 and 1990. On the other hand, various indicators of the harmful health and crime consequences of cocaine remained fairly stable over the same period. Using a variety of indirect sources of evidence—since direct data was not available—and a simple epidemiological model of the flow of individuals between nonuse, casual use, and heavy use, Everingham and Rydell estimated that while cocaine prevalence declined between 1983 and 1990, the total quantity of cocaine consumption remained fairly stable. According to their estimates, 22 percent of the current users of cocaine accounted for 70 percent of the total cocaine consumed in 1990. Their conclusion was that the decline in cocaine prevalence was primarily due to the cessation of use by casual experimenters, leaving a hard core of heavy, persistent users (Figure 2.1).11


This skew pattern is common in data on antisocial behavior; for example, roughly 5 percent of criminal offenders account for at least half of all crimes committed (see Moffitt, 1993).

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