Measuring different aspects of problem drug use: methodological developments (2nd edition) Editors: Nicola Singleton Rosemary Murray Louise Tinsley Home Office Online Report 16/06 The views expressed in this report are those of the authors, not necessarily those of the Home Office (nor do they reflect Government policy). Measuring different aspects of problem drug use: methodological developments Editors: Nicola Singleton, Rosemary Murray, Louise Tinsley Online Report 16/06 Acknowledgements Local and national estimates of the prevalence of opiate use and/or crack cocaine use, 2004/05 The authors of chapter 2 of this report would like to thank the following for their support and assistance in making possible the study this chapter describes. Colin Carroll, Eleanor Gallagher, Jennifer McKell, Chris Thexton and Anne Marie Ure, Centre for Drug Misuse Research, University of Glasgow. Andrew Jones at National Drug Evidence Centre, University of Manchester. Home Office staff including Chris May (CARAT data), Warren Evans, Lucy Cuppleditch and members of the PNC data team, and Natasha Garnham, Robin Moore and members of the OASys Data, Evaluation and Analysis Team (O-DEAT), who provided data for the study. Rosemary Murray and Nicola Singleton from the Drugs Analysis and Research Programme, who facilitated the provision of data from central sources and provided useful comment on reports and plans throughout the first sweep of the study. Members of the Steering Group including representatives from National Treatment Agency for Substance Misuse, Department of Health, the National Probation Service, HM Treasury and the Association of Chief Police Officers and also Patient Information Advisory Group, for their support for the project. Filip Smit, Trimbos Institute, Utrecht, The Netherlands and Ludwig Kraus, Institute for Therapy Research, Munich, Germany and colleagues in Drug Action Teams who have provided useful comments on the study. Research Ethics approval for the use of NHS data in this study was granted by the Scottish Multi-centre Research Ethics Committee (ref MRE00/54). Estimating the size of the UK illicit drug market The work described in chapter 4 of this report was produced as part of a Home Office funded project “Sizing the UK illicit drugs market” (contract RDS/04/160). The authors of chapter 4 are extremely grateful to Anne Line Bretteville-Jensen, Robin Fallows, Toni Makkai, Louise Tinsley, Peter Reuter, Nicola Singleton and Nigel South, for help and advice which improved the chapter enormously. Comments from staff of CIDA, FSS and NCIS are also gratefully acknowledged. The views expressed in this report are those of the authors, not necessarily those of the Home Office (nor do they represent Government policy). Any errors or misinterpretations are the authors’ responsibility. - i - Contents Acknowledgements i 1. Introduction 1 Overview and policy context 1 Estimating the number of problematic users 1 Drugs consumption and its social impact 1 2. Local and national estimates of the prevalence of opiate use and/or crack cocaine use, 2004/05 3 Summary 3 Background 7 Prevalence estimation methods 10 Data sources 13 Capture-recapture analyses 19 Multiple indicator analyses 22 Results 27 Discussion and conclusions 37 3. The economic and social costs of Class A drug use in England and Wales, 2003/04 41 Background 41 Results for 2003/04 42 Methodological and data update 44 4. Estimating the size of the UK illicit drug market 46 Summary 46 Objectives 48 Previous measurement attempts 48 Methodology 53 A review of data sources on drug use 56 Data reliability 59 Prices and quantities 62 Estimating the size of the arrestee population 70 Extension to the UK level 74 Baseline estimates 75 Adjustments for under-reporting 78 Comparison with earlier estimates 79 Comparison with other evidence 80 Conclusions and implications for further research 83 References 86 Appendix 1 MIM indicators 89 Appendix 2 Methodology for estimating the size of the UK illicit drugs market 99 Appendix 3 Data sources on drug use 104 Appendix 4 The impact of survey design on drug self-reports 107 Appendix 5 Prices and quantities 109 Appendix 6 A method for estimating the size of the arrestee population 113 Appendix 7 Conversion to a UK basis 115 Appendix 8 Adjustments for under-reporting 116 - ii - List of tables S.2.1 National prevalence estimates and rates per 1,000 population aged from15 to 64 with 95 per cent confidence intervals 4 S.2.2 Estimated number of problem drug (opiate and/or crack cocaine) users and opiate users by Government Office Region 4 S.2.3 Estimated number of crack cocaine users and drug injectors by Government Office Region 5 S.2.4 Estimated prevalence (rate per 1,000 population aged from 15 to 64) of problem drug (opiate and/or crack cocaine) use and opiate use by Government Office Region 5 S.2.5 Estimated prevalence (rate per 1,000 population aged from 15 to 64) of crack cocaine use and drug injecting by Government Office Region 6 2.1 Population estimates by Government Office Region, gender and age group (thousands), 2004 mid-year estimates 7 2.2 Summary of the number of DAT areas used as multiple indicator anchor points by Government Office Region 23 2.3 National prevalence estimates and rates per thousand aged from 15 to 64 with 95 per cent confidence intervals 28 2.4 Estimated number of problem drug (opiate and/or crack cocaine) users, opiate users, crack cocaine users and drug injectors by Government Office Region 28 2.5 Estimated prevalence of problem drug (opiate and/or crack cocaine) use, opiate use, crack cocaine use and drug injecting by Government Office Region (per thousand population aged from 15 to 64) 29 2.6 Prevalence estimates and 95 per cent confidence intervals (problem drug (opiate and/or crack cocaine) use and opiate use), by Government Office Region 30 2.7 Prevalence estimates and 95 per cent confidence intervals (crack cocaine use and drug injecting), by Government Office Region 30 2.8 Estimated prevalence (rate per 1,000 population aged from 15 to 64) of problem drug (opiate and/or crack cocaine) use and opiate use, by Government Office Region including 95 per cent confidence intervals. 31 2.9 Estimated prevalence (rate per 1,000 population aged from 15 to 64) of crack cocaine use and drug injecting, by Government Office Region, including 95 per cent confidence intervals. 31 2.10 Estimated gender breakdown for problem drug (opiate and/or crack cocaine) use by Government Office Region 32 2.11 Estimated gender breakdown for opiate use by Government Office Region 32 2.12 Estimated age group breakdown for problem drug (opiate and/or crack cocaine) use by Government Office Region 33 2.13 Estimated age group breakdown for opiate use by Government Office Region 33 2.14 Problem drug (opiate and/or crack cocaine) use prevalence rates per thousand population aged from 15 to 64 by gender and Government Office Region 34 2.15 Opiate use prevalence rates per thousand population aged from 15 to 64 by gender and Government Office Region 34 2.16 Problem drug (opiate and/or crack cocaine) use prevalence rates per thousand population by age group and Government Office Region 35 2.17 Opiate use prevalence rates per thousand population by age group and Government Office Region 35 3.1 Economic and social costs of Class A drug use associated with problematic drug use, 2003/04 43 3.2 Economic and social costs of Class A drug use associated with young recreational and older regular use, 2003/04 43 3.3 Summary of estimates of criminal justice costs and victim costs of crime in 2003/04 44 - iii - S.4.1 Baseline estimates of market size for England and Wales and the UK, 2003/04 46 4.1 Estimated total expenditures on illicit drugs, USA 1994-2000 ($ billions) 51 4.2 Calculation of total marijuana consumption, USA 1994-2000 51 4.3 Percentage of interviewees with positive drug test results who deny using the drug in question during the previous year 62 4.4 Unit value distributions from AS data 63 4.5 NCIS price series for 2000-2004 63 4.6 Drug purity (FSS estimates) 64 4.7 Distributions of drug purity, Jan-Sep 2004 65 4.8 Average quantity used by user type at typical episode, Australia 2001 67 4.9 Assumed values for mean price, quantity and purity, with assumed margins of error 68 4.10 Distribution of self-reported quantities consumed from AS data 69 4.11 Numerical interpretation of frequency-of-use questions 70 4.12 Population estimates 71 4.13 Available estimates relevant to measurement problem 72 4.14 Estimates of the arrestee population 74 4.15 Baseline estimates of market size for England and Wales and the UK 2003/04 76 4.16 Adjustments for under-reporting 79 4.17 Comparisons of new estimates with Bramley-Harker estimates for 1998 80 4.18 Drug seizures made by the police and other authorities in 2001 and 2002 81 4.19 Market share indicators 81 A1.1 Number of Income Support Claimants 89 A1.2 Number of Incapacity Claimants 89 A1.3 Number of Jobseeker’s Allowance Claimants 89 A1.4 Burglary 90 A1.5 Criminal Damage 91 A1.6 MIM indicator details – Drug Offences 92 A1.7 MIM indicator details – Fraud and Forgery 92 A1.8 MIM indicator details – vehicle and other theft 93 A1.9 MIM indicator details – violence against the person 94 A1.10 MIM indicator details – all crime 96 A1.11 MIM indicator details – number of people with a limiting long-term illness 98 A1.12 MIM indicator details – Population Density 98 A3.1 Main survey sources of drug use data 104 A3.2 Data available for OCJS non-respondents 105 A3.3 Data available for AS non-respondents 106