Capture-recapture methods to estimate prevalence indicators for the evaluation of drug policies

In the present paper several capture-recapture procedures in the presence of a single source are compared to estimate the size of the population of drug users that risks being registered for personal drug use under Italian law. It is the first time that this method is used in Italy for this particular subpopulation. Data sets are based on police registration data for the year 2007 and have been provided by the Italian Ministry of the Interior. In order to propose a means of evaluating the impact of demand-reduction policies, particular attention has been devoted to prevalence estimates for the younger age groups (those under 20 years of age), for whom prevalence can be considered as a good proxy for incidence; in fact, incidence indicators are more efficient in assessing the effect of policy intervention but are more difficult to estimate.