Significance levels are indicated in the tables, and allchanges described in the text as increases or decreases were tested and found to be significant at least at the .05 level, unless otherwise stated. Tables and text present prevalence measures in terms of both the number of drug users and the rate of drug use in the population. Data are also presented for four U.S. geographic regions and nine geographic divisions within these regions. The tables also present data by population density. Small metropolitan areas are MSAs with a population of less than 1 million.
Nonmetropolitan areas are areas outside of MSAs.
For some tables, small metropolitan areas are further classified as having either less than or greater than 250,000 population, and nonmetropolitan areas are classified as either urban or rural. In this report, all rural estimates are based on only nonmetropolitan rural areas. Other than presenting results by age group and other basic demographic characteristics, no attempt is made in this report to control for potentially confounding factors that might help explain the observed differences. The cross-sectional nature of the data limits the capability to infer causal relationships. The 1998 public use file will be available in early 2000.