Estimating the number of heroin users: a review of methods and empirical findings from The Netherlands.

This article reviews major methods applied to estimate the number of heroin users in a community, predominantly urban areas. The main focus is on applicability of methods to the available data. Methodologies are evaluated with regard to reliability, validity, and feasibility from the perspective of empirical findings, in particular in the Netherlands. Findings from Amsterdam and Rotterdam are presented in more detail in order to discuss major criteria for application of the capture/recapture and the nomination techniques.