A comparison of different methods for estimating the prevalence of problematic drug misuse in Great Britain

Aims. The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) has produced methodological guidelines for national drug prevalence estimation. This paper pilots the methods to estimate prevalence for Great Britain and provides a commentary on the methods and resulting estimates. Design. Three types of methodology were used to estimate prevalence: (a) the multiple indicator (MI) method, (b) multipliers applied to (i) drug-treatment records (ii) HIV estimates and (iii) mortality statistics and (c) the British/Scottish Crime Surveys. Setting. England, Scotland and Wales. Participants. Aggregated data on people recorded on databases and respondents in household surveys. Measurements. Prevalence estimates of different forms of problematic drug use. Findings. The estimates are 161 133 (range: 120 850-241 700) for people at risk of mortality due to drug overdose; 161 000-169 000 for people who have ever injected drugs; 202 000 (range: 162 000-244 000) problem opiate users and 268 000 problem drug users (all types). Conclusions. The multiple indicator method offers a comprehensive approach to estimating the prevalence of problematic drug use in the United Kingdom. Simple multiplier methods and household surveys also provide a range of estimates corresponding to different types of drug use in the United Kingdom. The current study suggests that previous national estimates of 100 000-200 000 were conservative. The new estimate of 161 000-266 000 should enable a more focused response. For further development of this method, reliable and timely estimates of anchor points are required for specific geographical areas such as cities or Drug Action Teams (DAT), as well as routine aggregation of drug indicators for these areas.