4. Estimating the size of the of illicit drug market – a critical review

Estimates of the drug market are frequently cited. However, both the veracity of the figures produced, and the methods used for their construction are often unclear. This presentation will critically review what methods have been used by studies in this area and make some recommendations for future work in this area.

This presentation will be based on around three sources. First a literature review of studies that have produce a market size estimate using both supply and demand side approaches. Second some innovative work conducted in Switzerland that has explored how multiple sources, including the analysis of wastewater residues, can inform a market size estimate. Third, a short consultation with experts who have been involved in drug market estimates at the national or international levels.

Despite estimates of the drug market often appearing in the media there are remarkably few robust studies available to inform a discussion on this topic. The studies that are available tend to have been conducted in only a few countries (particularly the USA and UK) and not all drugs are given equal attention. Two main approaches have been used, top-down supply side approaches and bottom-up demand side approaches. Supply side approaches are difficult to scientifically evolute as they depend on assumptions that are difficult to validate. The assumptions used in demand side approaches bring with them considerable uncertainty, but it may be possible to reduce this through future work. More recently some new data sources have come available that may have the potential to inform future studies in this area.

All approaches in this area have limitations and bring with them uncertainty. The discussion will consider the relative merits of different approaches and what lessons can be learnt from recent Swiss work in this area.