title: Estimating the prevalence of problem drug use in inner London: a discussion of three capture-recapture studies.
abstract: OBJECTIVE
  To provide an evidence base of estimates of the prevalence of problem drug use in inner London.
  
  
  METHODS
  Re-analysis of three capture-recapture studies using subjects aged 15-49 years, that aim to estimate the hidden population from analysing the overlaps between three data sources.
  
  
  METHODS
  Newham (1995) Camden and Islington (C&I) (1993/4) and Lambeth, Southwark and Lewisham (LSL) (1992).
  
  
  METHODS
  Each study collected data from three sources of problem drug users including: the Regional Drug Misuse Database, specialist drug agencies, HIV tests, social services, police arrests and court records. In LSL opiate users were analysed separately. The studies identified 1832 individuals in LSL, 543 in Newham, and 1321 in C&I.
  
  
  METHODS
  Poisson models were fitted to the data testing different interactions between the data sources representing potential dependencies. The simplest model was selected on the basis of its AIC score and log-likelihood ratio tests.
  
  
  RESULTS
  The number of hidden problem drug users were estimated to be 12,500 (95% CI 9600-16,100) in LSL with 4400 (3200-6100) opiate users; 7000 (5000-10,000) in C&I and 3800 (2000-7200) in Newham. The prevalence of problem drug use in those aged 15-49 was estimated to be 3.1% (2.5-3.9%) in LSL with 1.3% (1.0-1.6%) opiate users; and 3.6% (2.7-4.9%) and 3.3% (1.9-5.7%) in C&I and Newham, respectively.
  
  
  CONCLUSIONS
  Despite the inherent problems with capture-recapture methods, our three studies establish an evidence base for estimates of problem drug use in London. It is important that a larger study is carried out in London.
authors.affiliation: Centre for Research on Drugs and Health Behaviour, Imperial College School of Medicine, London, UK. m.hickman@ic.ac.uk
authors.forename: M
authors.initials: M
authors.lastname: Hickman
authors.forename: S
authors.initials: S
authors.lastname: Cox
authors.forename: J
authors.initials: J
authors.lastname: Harvey
authors.forename: S
authors.initials: S
authors.lastname: Howes
authors.forename: M
authors.initials: M
authors.lastname: Farrell
authors.forename: M
authors.initials: M
authors.lastname: Frischer
authors.forename: G
authors.initials: G
authors.lastname: Stimson
authors.forename: C
authors.initials: C
authors.lastname: Taylor
authors.forename: K
authors.initials: K
authors.lastname: Tilling
mesh_terms: D000293:Adolescent; D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D015658:HIV Infections / Q000453:epidemiology; D006801:Humans; D008131:London / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D016012:Poisson Distribution; D011157:Population Dynamics; D015995:Prevalence; D019966:Substance-Related Disorders / Q000453:epidemiology*; D014504:Urban Health