title: Appropriateness and execution challenges of three formal size estimation methods for high-risk populations in India.
abstract: OBJECTIVE
  To describe formal, external to programme methods for size estimation of high-risk populations and compare execution challenges and validity of results.
  
  
  METHODS
  A cross-sectional HIV risk behavioural and biological survey was implemented among 24, 10 and five female sex workers, high-risk men who have sex with men and injecting drug user survey groups, respectively. Size estimates were calculated using three formal methods: capture-recapture, the multiplier method and the reverse tracking method (RTM), a new method.
  
  
  METHODS
  Estimates were compared with each other and programme data.
  
  
  RESULTS
  In general, when appropriately executed, formal methods produced smaller estimates to programme data, although the RTM tended to be closer to programme estimates.
  
  
  CONCLUSIONS
  Capture-recapture requires some knowledge of site location. It can be used as a community mobilization measure at the initiation of a programme. The multiplier method presumes the existence of high quality external data and requires care in selecting the appropriate multiplier. All size estimation methods require careful planning and a full understanding of population dynamics and limitations of data. Before selecting a size estimation method, one must be aware of the strengths, weaknesses and applicability of each method. Use of size estimation methods in large-scale programmes should be considered carefully with adequate importance given to planning and implementation.
authors.affiliation: National Institute of Epidemiology, Chennai, India. nieibbadmg@gmail.com
authors.forename: Selvaraj
authors.initials: S
authors.lastname: Vadivoo
authors.forename: Mohan D
authors.initials: MD
authors.lastname: Gupte
authors.forename: Rajatashuvra
authors.initials: R
authors.lastname: Adhikary
authors.forename: Anjalee
authors.initials: A
authors.lastname: Kohli
authors.forename: Boopathi
authors.initials: B
authors.lastname: Kangusamy
authors.forename: Vasna
authors.initials: V
authors.lastname: Joshua
authors.forename: A K
authors.initials: AK
authors.lastname: Mathai
authors.forename: Kishore
authors.initials: K
authors.lastname: Kumar
authors.forename: Mandar
authors.initials: M
authors.lastname: Mainkar
authors.forename: Prabuddhagopal
authors.initials: P
authors.lastname: Goswami
mesh_terms: D004812:Epidemiologic Methods; D005260:Female; D015658:HIV Infections / Q000635:transmission; D018451:Homosexuality, Male / Q000706:statistics & numerical data*; D006801:Humans; D007194:India / Q000453:epidemiology; D008297:Male; D011156:Population Density; D012309:Risk-Taking; D011477:Sex Work / Q000706:statistics & numerical data*; D015819:Substance Abuse, Intravenous / Q000453:epidemiology*