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

In this paper we compare capture-recapture procedures in the presence of a single source, to estimate the size of the population of drug users who risk being registered for personal use of drugs under Italian law, which for the first time implements this method 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 how the impact of policies could be evaluated, particular attention has been devoted to prevalence estimates for lower age classes (under 20 years), where 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.