Overall, 16,195 IDUs were enrolled across the study. Study sample sizes ranged from 160 to 5305, with the average number of 1,350 per study. The average age across samples was 35.4 years (range = 31.0 – 39.2; k = 8). Study participants were predominantly recruited from venues that served active drug users, including substance abuse treatment clinics, service organizations, or defined communities. Half (k = 6) of the studies paid incentives to individuals for participation in the study. A complete summary of the outcome measures generated from each citation appears in Table 1.