Validation of a regional drug misuse database: implications for policy and surveillance of problem drug use in the uk

Introduction

The eight regional drug misuse databases constitute the largest investment (about £100 000 each annually) in drugs surveillance in England. Along with databases in Scotland and Wales, they provide the main intelligence on problem drug takers, including monitoring government targets.1 They were established because of the lack of information on clients of drug agencies2 but have attracted criticism for not properly informing policymakers of the extent of drug use and not accurately assessing client volume.3 We performed a study in North Thames to assess the level of underreporting of “episodes” (new clients or clients who reattend after an absence of six months4) to the regional database and the relation between episodes and the number of clients and prevalent drug takers attending agencies in a year.

Methods and results

Over 80% of reports to the North Thames database come from 62 specialist drug agencies. These were categorised according to type, and a sample selected using random number tables: 3 from 8 drug dependency units, 9 from 27 statutory community based drug services, 5 from 16 non-statutory community services, 2 from 9 residential rehabilitation units, and 1 of 2 needle exchanges. Two statutory community services refused and were not replaced. A further six agencies which did not participate in the database were identified. Two were selected randomly (both non-statutory community services) and agreed to participate, making a final sample of 20 agencies (29%). A researcher visited the agencies (April-December 1995) to collect a standard dataset on everyone who attended during 1994. These were matched with individual agency reports for 1994 and then against the whole dataset in the database using initials, date of birth, sex, and, in uncertain matches, postcode, ethnic group, drug problem, and date of report.

Altogether 5673 clients, 4543 episodes, and 5136 prevalent problem drug takers were collected from the 20 agencies. There were fewer episodes and drug takers than clients because only new clients and those who reattend after a six month gap generate a new episode and drug takers may attend more than one agency. The 1 summarises the under-reporting. The level of reporting differed by type of agency: 9% of episodes at drug dependency units were unreported compared with 20% for non-statutory community services, 31% for statutory community services, 40% for residential rehabilitation units, and 63% for the needle exchange. About half the 40% shortfall between database reports and agency records of clients (excluding the two agencies which did not report) was due to under-reporting (998) with the remainder due to the “episode” definition excluding continuing clients who have not had six months between attendances (1037).

Comment

This study is the first to assess systematically the coverage and validity of the drug misuse database. Our estimates, generalisable to North Thames, also represent the best available for adjusting national figures. Though an earlier study estimated underreporting at less than 3%, the sample was self selected from agencies with the largest number of reports and biased towards high levels of reporting.5 Most specialist drug agencies in North Thames participate in the regional database, and in terms of coverage (including completeness of reporting) it compares favourably with other surveillance systems in the UK. Nevertheless, the database does not measure the prevalence of known problem drug takers, which means it is inadequate for planning services and provides a false picture of trends of visible drug use. The database needs to be changed rather than abandoned since policymakers and health services need information on drug users in contact with services.