To identify data sources and methods for estimating the population proportion of PWID in the United States, we developed search strategies to identify relevant reports published from 1993 through 2008 (see Checklist S1). The initial phase (Phase 1) included an automated, systematic search of 5 electronic databases (Medline, CINAHL, PsycInfo, Sociological Abstracts, and Cochrane). We cross-referenced multiple search terms (i.e., keywords and each database's index terms) in 3 domains: (1) measurement descriptors (prevalence, epidemiologic methods, measure, survey, assessment); (2) injection drug use (substance/drug, use/abuse, intravenous/inject/parenteral); and (3) geography (some or all of the U.S.). We kept search terms broad to avoid overlooking any relevant references that might provide data or different methods for estimating the PWID population proportion.
