The effectiveness and cost-effectiveness of diversion and aftercare programmes for offenders using class A drugs: a systematic review and economic evaluation

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This entry is our analysis of a study considered particularly relevant to improving outcomes from drug or alcohol interventions in the UK. The original study was not published by Findings; click Title to order a copy. Links to other documents. Hover over for notes. Click to highlight passage referred to. Unfold extra text Unfold supplementary text The Summary conveys the findings and views expressed in the study. Below is a commentary from Drug and Alcohol Findings.

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The effectiveness and cost-effectiveness of diversion and aftercare programmes for offenders using class A drugs: a systematic review and economic evaluation.

Hayhurst K.P., Leitner M., Davies L. et al.
Health Technology Assessment: 2015, 19(6).


[Consultation draft subject to amendment and correction.] Although diversionary schemes continue to be a strategic focus for policy in relation to tackling drug-related problems, the evidence base for the effectiveness of these schemes is not (yet) in place.

Summary It is estimated that half of recorded acquisitive crime in the UK is drug related (1 2). However, the relationship between drug use and acquisitive offending is complex, rather than causal (3 4 5). For example, the Drug Treatment Outcomes Research Study (DTORS) evaluation found that behavioural and demographic factors were stronger predictors of involvement in acquisitive crime than spending on drug use, suggesting that the need to finance drug use is not necessarily the main factor driving acquisitive offending by drug users.

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The Drug Interventions Programme (DIP) was introduced in the UK in 2003, providing a model for working with drug-using offenders at each stage of their contact with the criminal justice system. One of the main aims was to divert people from the criminal justice system and into treatment using both voluntary and coercive elements.

The featured study asked whether or not diversion (plus aftercare) programmes improve outcomes or reduces costs compared with not offering them. In order to answer this question the researchers reviewed other studies already carried out on this topic, and developed an economic model to look at the costs and possible benefits of diversion using data from national databases, published studies, and a sample of English heroin and/or crack cocaine users who were arrested.

Sixteen studies met inclusion criteria for the effectiveness review. Ten were US-based, four were set in the UK, one in Canada, and one in Australia. The US evaluations were dominated by drug court diversion interventions, and led to an over-representation of American (Californian) methamphetamine users (over 99% of participants) and a focus on the impact of the Californian Substance Abuse and Crime Prevention Act referral.

Diversion programmes were voluntary, court mandated, or monitored services that sought to identify and divert problem drug users to treatment at any point within the criminal justice system. Aftercare was defined as care which followed diversion and treatment, excluding that following prison or non-diversionary drug treatment.

Main findings

The review, which involved a narrative synthesis (exploring and outlining the extent, nature and quality of the available evidence in this area) and a meta-analysis (combining data from similar studies to produce single estimates of outcomes) was only partially successful in its aim to understand the effectiveness of diversion schemes.

A potential but small impact of interventions on drug use outcomes was identified. Calculating ‘odds ratios’ – the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure – researchers arrived at estimates of 1.7 for reduced primary drug use and 2.6 for reduced use of other drugs, where 1.0 indicates that exposure does not affect odds of outcome and a figure of more than 1.0 indicates that exposure associated with higher odds of outcome. In comparison with users of other primary drugs, class A drug users were significantly more likely to be expelled or drop out of treatment early (odds ratio of 0.89).

The use of conceptually different measures to evaluate the outcome of reductions in offending behaviour prevented meta-analysis. The results of individual studies pointed to minimal impact of interventions on offending. The outcomes of general arrest were slightly more equivocal, with one of three studies reporting a small but statistically significant reduction in re-arrest as a result of treatment. Few studies addressed health-related outcomes; noticeably absent were physical or mental health, or longer-term impacts, such as hospital admission or mortality or other potential outcomes such as employment, training or family support/conflict. The outcome measures used were also too diverse to draw any substantive conclusions regarding the impact of treatment.

There were no studies that could be included in the cost-effectiveness review – the main reason for exclusion being that studies did not conduct a full economic evaluation that compared diversion to an alternative and included a measure of health benefit or estimated the cost–benefit.

The economic model highlighted a lack of evidence around the cost-effectiveness of diversion in the UK, due to limitations with the data and uncertainty about structural aspects of the evaluation. This meant that it was not clear whether or not DIP has no impact compared to no DIP or whether or not the evidence was insufficient to identify a difference. The likelihood that diversion is cost-effective was between 48% and 52% based on the assumption that decision-makers were willing to pay up to £30,000 to gain one additional QALY for arrested drug users.

The primary analysis assigns all DIP and treatment costs at the start of the 1-year time horizon. It is assumed that there will be no additional DIP or treatment costs following subsequent offences. This gives an accurate estimate of the total DIP costs and community-based treatment for the first year (estimated from the DDW). However, it may underestimate the costs of prison-based treatment services for those who reoffend and receive a prison sentence. Increasing the costs of prison sentences did not change the overall results of the analysis.

For the primary analysis, the probability and costs of recorded offences, arrests, type of offence and whether a person received a prison or community sentence was assumed to be the same for the DIP and no DIP arms of the model. This was based on the assumption that the main effect of a CJS treatment referral was on entry into treatment. A linked assumption is that subsequent offending behaviour depended on engagement with treatment and the effectiveness of treatment services. It is possible CJS treatment referral also affected the severity of offending behaviour and the CJS and non-CJS costs of offences. This was tested in sensitivity analysis using detailed data from the DDW. However, it is important to note that the DDW data may reflect selection biases. These biases could be due to differences in the characteristics of people who received CJS treatment referral via the DIP and those who did not.

The authors’ conclusions

The review, drawn from mostly US-based research, found that diversion may reduce drug use, while its effect on reducing offending is unclear. Few studies used the same outcome measures. Only half of the included studies reported outcomes for non-drug-related offences. Studies were generally of poor methodological quality and characterised by modest sample size, a high attrition rate, retrospective data collection, limited follow-up, and no random allocation of participants. There was also evidence of publication bias in the available literature.

No studies were able to answer the question of whether or not diversion can save money. The economic model, which focused on the Drug Interventions Programme (DIP) in the UK, found that diversion may be cost-effective. However, there was uncertainty about the relevance and quality of data, which rendered it difficult to conclude whether or not diversion is clinically effective or cost-effective.

Diversion and aftercare programmes display many of the characteristics of a complex intervention. The systematic review and economic evaluation have highlighted that they are multifactorial with the potential for each component to have an independent effect on outcome. In addition, there is the potential for one or more components to mediate or modify the impact of other components on outcome.


Findings logo commentary The featured paper defined diversion as the range of voluntary, court-mandated, or monitored services that filter people into treatment and away from the criminal justice system. The review of previous studies was based overwhelmingly on programmes in the United States, which tend to be court-mandated, whereas the economic model was based on the UK Drug Interventions Programme (DIP) which identifies two possible pathways that service users can follow:
• identification by enforcement;
• identification by proactive engagement.

In 1999, Drug and Alcohol Findings published an article by Professor Philip Bean on whether the evidence shows that coercing drug-related offenders into treatment works. The essential practice points from this article were that:

“How an addict is exposed to treatment seems irrelevant. What’s important us that they are brought into an environment where intervention occurs; the more routes into this environment the better.”
“More treatment time leads to better outcomes; coercion can improve retention.”
“Treatment programmes for legally coerced clients should be lengthy, provide a high level of structure, be flexible yet firm, and undergo regular evaluation.”

An important finding of this review was that the included evaluations did not include assessment of the acceptability and feasibility of the interventions. In addition, it is not clear what proportion of drug-using offenders will receive a DIP assessment/drug test. The estimate used for the sensitivity analysis was 14%, but this was based on expert opinion. National statistics suggest that 57,000 people arrested had a formal DIP assessment in 2009. However, it is unclear how many people arrested were eligible for a DIP assessment, with or without drug testing. In addition, the proportion of treatment referrals from DIP is approximately 13% of all referrals and 30% of new referrals. There may be a number of reasons why DIP is, or is not, used and evidence about these issues is required.

Mentioned at the start of the featured paper was the Drug Treatment Outcomes Research Study (DTORS) – a national programme for assessing the progress of patients starting drug treatment in England. Rather than setting up treatments to be tested on patients allocated by researchers, the study simply tracked what happened after patients presented in the normal way to usual drug treatment services. For this reason it was unable to compare the effectiveness of one treatment with another (caseload differences could invalidate such a comparison), but was able to shed light on the progress typically achieved during and after typical treatments.

DTORS found that clients presenting for treatment via criminal justice routes were retained as long and did as well those from other referral sources. However, criminal justice routes were no better at extending treatment to first-time entrants, and over half who came to treatment this way said they would have come anyhow, suggesting that resources might best be focused on the relatively few drug users who would not have entered treatment via another route. It also found that crime went down as the need to commit it to raise money for drugs also fell, but strangely there was no clear correlation between the criminal income of each participant at different stages in the study and the extent of their drug use.

National responses to crime and substance use are shaped by the following pillars of British drug and alcohol policy (each appraised in the Effectiveness Bank):
UK Government Modern Crime Prevention Strategy (2016): The Justice Secretary and Lord Chief Justice have set up a joint working group to investigate the problem-solving court model, which can include diversion from the mainstream criminal justice system where the offender opts in to the problem-solving court – often as an alternative to a prison sentence – and agrees to undergo appropriate treatment and behaviour change interventions. Progress is overseen by the judiciary who hear reviews at court and support the offender through rehabilitation.
UK Government drug strategy (2017): The strategy cites strong evidence to link drug treatment to reductions in offending and supporting people to address their dependence, and therefore regards treatment as critical to tackling the risk of reoffending. Alongside punitive sanctions, the criminal justice system should consider use of health-based, rehabilitative interventions to address the drivers behind the crime and help prevent further substance misuse and offending. Liaison and diversion services, for example, enable offenders with mental health, substance use and other complex needs to be directed towards appropriate health interventions from police stations or courts.
Scottish Government’s strategy to improve health by preventing and reducing alcohol and drug use, harm and related deaths (2018): Scotland has pledged to take a public health approach to justice, aiming for vulnerable people to be diverted from the criminal justice system wherever possible. “Diverting those with problematic alcohol and drug use away from the justice system and into treatment support, and other interventions that reduce harm and preserve life, is essential. This approach needs to run through how the police lead the work to control the supply of drugs, sentencing, the provision of treatment and support in prison setting, as well as supporting continuity of care on release.”
Prison Drugs Strategy (2019): A three-point plan for tackling the presence of drugs and drug use problems in UK prisons launched by the national agency responsible for prison and probation services. Following the themes of the UK Government drug strategy, it focuses on restricting supply, reducing demand, and building recovery.

This draft entry is currently subject to consultation and correction by the study authors and other experts.

Last revised 06 May 2019. First uploaded 11 April 2019

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