title: A method to estimate total entry to hard drug use: the case of intravenous drug use in Norway.
abstract: OBJECTIVE
  Epidemiological measures such as the prevalence and incidence of hard drug use are important tools for evaluating drug situations and drug policies. Models for drug use trajectories illustrate how temporary and lasting cessation of and relapse into hard drug use are other important elements in the overall picture of change in hard drug use over time. Estimating the total entry to hard drug use broadens the knowledge of the change in such use.
  
  
  METHODS
  The entry rate for hard drug use is defined as the sum of incident cases and relapses and estimated based on successive prevalence estimates and cessation rates.
  
  
  RESULTS
  The entry rate, as applied to the Norwegian case of intravenous drug use, increased from the mid-1980s to a peak in 2000, decreased up to 2003 and stabilized thereafter. The peak in Oslo appeared earlier (1998). The estimated level of the entry rate is sensitive to the rate of cessation.
  
  
  CONCLUSIONS
  We conclude that it is possible to expand the description of hard drug use epidemics beyond estimates of prevalence and incidence. The entry rate supplies a useful tool for our understanding of drug situations and decision making regarding drug policies.
authors.affiliation: Norwegian Institute for Alcohol and Drug Research, Oslo, Norway. eja@sirus.no
authors.forename: Ellen J
authors.initials: EJ
authors.lastname: Amundsen
authors.forename: Anne Line
authors.initials: AL
authors.lastname: Bretteville-Jensen
authors.forename: Ludwig
authors.initials: L
authors.lastname: Kraus
mesh_terms: D006801:Humans; D015994:Incidence; D008962:Models, Theoretical; D009664:Norway / Q000453:epidemiology; D015995:Prevalence; D012008:Recurrence; D013223:Statistics as Topic / Q000379:methods*; D015819:Substance Abuse, Intravenous / Q000175:diagnosis / Q000453:epidemiology* / Q000209:etiology*