Table 2 shows the estimated population proportion of lifetime PWID overall and for males and females for each population-based survey and the combined estimates from the meta-analysis. The overall combined estimate for the ever recall period was 2.6% (confidence interval [CI]: 1.8%–3.3%). As noted, Q statistics and I2 indicated heterogeneity of results across the surveys (Q2 = 45.1, P <.0001, I2 = 95.6). The combined estimate for males was 3.6% (CI: 2.4%–4.8%) and for females was 1.6% (95% CI: 1.1%–2.0%). Applying these proportions to the U.S. population age 13 years or older for 2011, we estimate that approximately 6,612,488 adults and adolescents ever injected drugs, with a range from 4,583,188 to 8,641,788 persons; using the sex-specific proportions an estimated 4,532,348 males (range: 3,040,447–6,024,250) and 2,059,709 females (range: 1,513,969–2,605,450) ever injected drugs.
