title: How much of the cocaine market are we missing? Insights from respondent-driven sampling in a mid-sized American city.
abstract: BACKGROUND
  Studying markets for illegal drugs is important, but difficult. Data usually come from a selected subset of consumers, such as arrestees, treatment clients, or household survey respondents. There are rarely opportunities to study how such groups may differ from other market participants or how much of total consumption they represent.
  
  
  METHODS
  This paper uses respondent-driven sampling (RDS) of drug users in a mid-sized American city to estimate the shares of cocaine (powder and crack) users and expenditures that are attributable to different combinations of these groups.
  
  
  RESULTS
  We find that those arrested in the last year accounted for 34% of past-month cocaine users and 40% of past-week cocaine spending in the RDS sample. Augmenting past-year arrestees with those who received treatment in the past year increases these values to 44% (users) and 55% (spending).
  
  
  CONCLUSIONS
  Our results suggest that estimates based only on people who were arrested and/or treated in the past year would have to be inflated by 100-200% to capture the market totals. Adding those who own or rent their place of residence increased coverage in this study to 76% (users) and 81% (spending), suggesting that in theory the inflation factor could be reduced to 23-32% by supplementing data on arrestees and treatment populations with household data, although in practice rates of under-reporting by survey respondents may make coverage (sampling frame) a secondary concern for household surveys.
authors.affiliation: Carnegie Mellon University's Heinz College, 5000 Forbes Avenue, Pittsburgh, PA 15213, United States. Electronic address: caulkins@andrew.cmu.edu.
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Caulkins
authors.affiliation: Social Policy Research Associates, 1333 Broadway, Oakland, CA 94612, United States. Electronic address: jesse_sussell@spra.com.
authors.forename: Jesse
authors.initials: J
authors.lastname: Sussell
authors.affiliation: RAND Corporation, 1776 Main Street, Santa Monica, CA 90401, United States. Electronic address: kilmer@rand.org.
authors.forename: Beau
authors.initials: B
authors.lastname: Kilmer
authors.affiliation: Human-Computer Interaction Institute, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, United States. Electronic address: amkasunic@gmail.com.
authors.forename: Anna
authors.initials: A
authors.lastname: Kasunic
mesh_terms: D000328:Adult; D003042:Cocaine; D019970:Cocaine-Related Disorders / Q000453:epidemiology* / Q000534:rehabilitation; D016578:Crack Cocaine; D003415:Crime / Q000706:statistics & numerical data; D055030:Drug Users; D005260:Female; D006801:Humans; D013287:Illicit Drugs; D008297:Male; D015995:Prevalence; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires; D014768:Virginia / Q000453:epidemiology
chemical_list: D016578:Crack Cocaine; D013287:Illicit Drugs; D003042:Cocaine
keywords: Cocaine; Drug markets; Drug policy; Drug spending; Hidden populations; Respondent-driven sampling