How to explain the considerable disparity between self-declared drug use and available income?

The results of the study indicate a massive disparity between income (legal and criminal) and spending on illicit drugs, with half of our sample declaring no funding despite a mean spending of over £900 every 28 days. Most unemployed people, including class A drug users, claim benefits of £200-300 per month. ⁵ It seems extremely unlikely that drug use at this level is funded by gifts from relatives or friends. The street drug prices were compiled from a variety of sources, including the National Criminal Intelligence Agency and 80 front-line drug agencies, police forces and drug action teams in 20 towns and cities throughout the UK. ³ The prices of typical quantities of illicit drugs are displayed for the major conurbations throughout Britain. As this information was obtained from reports of staff, outreach workers and service users attending local treatment agencies, it is likely to be reliable.

The other explanation for the disparity between reported drug use and spending is the falsification of information provided at interview by the service users. Admittedly, it is possible that users could exaggerate their consumption, but they would have little reason to do this to the extent revealed by the study. Moreover, other studies have suggested that typical class A drug users in Britain spend £40 per day (around £1000 per month) on heroin and often more on cocaine. ^{Reference Luty, Perry, Umoh and Gormer6,Reference Gossop7} Many surveys have concluded that self-reporting of drug use is reliable and valid when events are recent and individuals do not face negative consequences. ^{Reference McLellan, Luborsky, Woody, Griffith, Evans and Barr8–Reference Darke12} For example, the UK National Treatment Outcome Research Study reported that the concordance rate between self-reported use and results from a urine specimen for heroin and cocaine was 92%. Only 2-3% of clients who reported not using heroin or cocaine tested positive. ^{Reference Gossop, Marsden and Stewart13} Hser et al assessed the reliability of retrospective self-report by 323 drug addicts at a 10-year interval with respect to opiate use and criminality. The diagnostic accuracy and predictive power of the self-report was found to be very high (over 80%). ^{Reference Hser, Anglin and Chou14} In regard to self-report of cocaine use, Simpson et al reported that 8.8% of people denied cocaine use but subsequently tested positive. This was based on a random sample of 352 interviewees who presented with cocaine misuse as part of the US Drug Abuse Treatment Outcome Study (DATOS). ^{Reference Simpson, Joe, Fletcher, Hubbard and Anglin15} However, these results are based on prolonged interviews in research samples rather than brief initial assessments in routine clinical teams where self-report may be less reliable.

The most likely explanation for the disparity between drug use and funding is that individuals are not reporting criminal activity. There is a vast body of research on self-report and concealment of delinquent and deviant activity including crime and sexual behaviour. ^{Reference Farrington16–Reference Weinhard, Forsyth, Carey, Jaworski and Durant20} It is also self-evident that many service users who are on court diversion programmes (such as the drug rehabilitation requirements) are unlikely to admit to illegal activity as this will be reported automatically to the court during their monthly reviews.

TOP and MAP

The Maudsley Addiction Profile (MAP) is a well-validated, brief, semi-structured interview developed to assess the substance use, risk-behaviour, health and social functioning of illicit drug users. ^{Reference Luty, Perry, Umoh and Gormer6} A health professional is required to complete the various sections, which takes approximately 12 minutes. There is no requirement for formal training to use the MAP. There is considerable overlap between the MAP and the TOP form and they were produced by many of the same authors. Both instruments are completed by clinicians following an interview with the clients, both have excellent psychometric properties (with correlation coefficients exceeding 0.75 between different indices) and have been validated in samples of several hundred clients at more than 50 community drug and alcohol services. ^{Reference Marsden, Farrell, Bradbury, Dale-Perera, Eastwood and Roxburgh1,Reference Luty, Perry, Umoh and Gormer6} They are relatively short (although TOP is significantly shorter) and are eminently practicable for use in front-line clinical services, although the researchers were frequently made aware of complaints by staff regarding the ever increasing and often irrelevant paperwork required by substance misuse services and mental health services in general. It would be highly desirable if the TOP form could be used to replace, rather than supplement, some of the other documentation often known as the ‘basic data-set’.

Are self-reports valid?

Problems with the validity of self-reported criminal activity in routine clinical settings have previously been observed in relation to the Maudsley Addiction Profile. ^{Reference Luty, Perry, Umoh and Gormer6} Of the 206 service users in this study, 96 were not working and denied committing any acquisitive crimes in the previous month, although they spent an average of £595 (s.e. = 96) on heroin and cocaine over this period. It is difficult to see how they were able to fund this illicit drug use without recourse to criminal activity, particularly as their total income from benefits amounted to only £230 per month each, and this includes payments to cover food and accommodation. Even with enhancements for disability or child support, this amount remains less than £500 per month. ⁵ It is possible that these individuals were receiving an undeclared income from informal work as well as fraudulently claiming unemployment benefits. However, it seems unlikely that they were willing to reveal the amount they were spending on illicit drugs and yet withhold information on undeclared employment.