Odds ratios describing the relative risk for each age-by-gender group (12–14, 15–17, 18–20 and 21–23), relative to the combined gender 24–34 year age group, were computed separately for all 20 administrations of the NHSDA/NSDUH that assessed binge drinking. These results are plotted by year, in Figure 1 for males, and Figure 2 for females. Results of trend analyses for these data are shown in Table 2, and corresponding trend-lines are included in the Figures. Table 2 lists interaction odds ratios (Trend OR) that describe the average per-year change in age-category odds ratios over time. For example, a per-year odds-ratio of 0.98 corresponds to an average 2% reduction in odds per-year, or an overall reduction in odds of 43% over the 27 years covered by the surveys (1–0.9827). To facilitate the interpretation of the overall change in odds, trend line estimates of relative odds for each age-by-gender groups for the first and last survey years analyzed (1979 and 2006) are also listed in Table 2.
