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.