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.

Research methods for illegal drug use in hidden populations: summary report of a European invited expert meeting.

An Invited European Expert Group Meeting was held in Rotterdam that focused on research methods for hidden populations using illicit drugs. Experts from most European Community member states participated and contributed state-of-the-art presentations on various research methodologies. Attention was paid to the more quantitatively oriented research methods, such as surveys using questionnaires, interviews, and routine statistics from treatment and criminal justice as well as to more ethnographically oriented research methodologies. Recommendations were formulated for the near future: research methodology needs to meet all the classical methodological criteria, such as clear definitions, tests on reliability and validity, and clear sampling procedures. Interfacing methods is the key phrase. More quantitatively oriented methods, such as interviewing a random sample from a household survey, seem unsuitable for research on illicit drugs, except perhaps for the use of cannabis. A multifactorial problem, such as illicit drug use and related problems, should be approached in a multidisciplinary way; that is, the integration of different research methodologies. Comparability between individual research projects in different countries requires not only technical adjustments of the data, but also a "framework for communication." Data always need to be interpreted in terms of cultural context. A similar framework should enhance studies with respect to comparison of drug policies and their consequences in different cities or countries.

Temporal and social contexts of heroin-using populations. An illustration of the snowball sampling technique.

Snowball sampling is a method that has been used in the social sciences to study sensitive topics, rare traits, personal networks, and social relationships. The method involves the selection of samples utilizing "insider" knowledge and referral chains among subjects who possess common traits that are of research interest. It is especially useful in generating samples for which clinical sampling frames may be difficult to obtain or are biased in some way. In this paper, snowball samples of heroin users in two Dutch cities have been analyzed for the purpose of providing descriptions and limited inferences about the temporal and social contexts of their lifestyles. Two distinct heroin-using populations have been discovered who are distinguished by their life cycle stage. Significant contextual explanations have been found involving the passage from adolescent peer group to criminal occupation, the functioning of network "knots" and "outcroppings," and the frequency of social contact. It is suggested that the snowball sampling method may have utility in studying the temporal and social contexts of other populations of clinical interest.