Effect of drug law enforcement on drug-related violence: evidence from a scientific review
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This entry is our analysis of a review or synthesis of research findings considered particularly relevant to improving outcomes from drug or alcohol interventions in the UK. The original review was not published by Findings; click Title to order a copy. The summary conveys the findings and views expressed in the review. Below is a commentary from Drug and Alcohol Findings.

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Effect of drug law enforcement on drug-related violence: evidence from a scientific review.

Werb D., Rowell G., Guyatt G. et al.
Vancouver: International Centre for Science in Drug Policy, 2010.

The first systematic review of this issue cautions that heightened drug enforcement which fails to curtail the illicit market in drugs can generate drug-related violence, raising the overall level of violence in societies where such markets are widespread and endemic.

Summary This review from the International Centre for Science in Drug Policy noted that research from many settings has demonstrated clear links between violence and the illicit drug trade, particularly in urban areas. While violence has traditionally been seen as resulting from the effects of drugs on users (eg, drug-induced psychosis), violence in drug markets and in drug-producing areas such as Mexico is increasingly understood as a way for drug gangs to gain or maintain a share of the lucrative illicit market.

In the light of the growing emphasis on evidence-based policy-making, and the severe violence attributable to drug gangs in many countries, it was decided to conduct a systematic review of all available English-language research on law enforcement's impact on violence related to illicit drug markets. The theory being tested was that increasing expenditure on or increasing the intensity of drug law enforcement would be associated with lower levels of violence.

A search was undertaken using electronic databases, Academic Search Complete, PubMed, PsycINFO, EMBASE, Web of Science, Sociological Abstracts, Social Service Abstracts, PAIS International and Lexis-Nexis. the Internet Google and Google Scholar. and article reference lists, from the earliest dates these facilities covered up to October 2009. This yielded 306 reports of which 15 met the review's criteria. Studies published in peer-reviewed journals, abstracts from international conferences, and publications from governments and non-governmental organisations which reported on a link between drug law enforcement, illicit drug strategies, and violence. Editorials, advocacy articles, and studies of police violence were excluded, as were studies focused on violence associated with military action against insurgencies funded through the drug trade. Thirteen of the studies were from North America and two from Australia. Contrary to expectations, across all 15 studies, 13 found that increasing drug law enforcement intensity was associated with greater rates of drug market violence; details below.

Eleven of the studies traced the link in different locations and over time between indices Such as drug arrests as a proportion of total arrests, police expenditure, number of police officers, and drug seizure rates. of the extent of drug law enforcement on the one hand, and records of violence, violent crime, or murder on the other. Each attempted to adjust Using regression analyses. for other influences in order to isolate the impact of enforcement levels. Nine of these 11 studies found statistically significant increases in violence as drug law enforcement increased. Another two studies found either no relationship or a different one in different cities. Additionally, two studies used hypothetical data to model the potential impact of intensified drug enforcement; one model suggested decreased violence, the other increased. Finally, two Australian studies based their conclusions, not on statistical tests, but on the observations of researchers and interviews with people involved with a drug market or with its policing. They found that though enforcement persuaded some dealers to leave a market, others willing to take higher risks entered. The result was that street dealing interactions became more volatile, leading to more violent disputes which contributed to an increase in killings and non-fatal shootings.

The reviewers concluded that evidence to date suggests that increasing the intensity of law enforcement interventions to disrupt drug markets is unlikely to reduce drug gang violence. Drug-related violence, gun violence, high murder rates, and the enrichment of organised crime networks, are likely to be a natural consequence of prohibitions against drug use and/or dealing. Increasingly sophisticated and well resourced ways of disrupting drug distribution networks may unintentionally increase violence. Alternative models for drug control may need to be considered if drug supply and drug-related violence are to be meaningfully reduced.

Findings logo commentary The featured report based on research retrieved to October 2009 has been updated to January 2011 in a journal article also analysed by Findings.

Caveats outlined in this summary are expanded on under the subheadings below. The unique value of this report is that apparently it is the first to systematically evaluate research on the impact of drug law enforcement on violence. It cautions that heightened enforcement which fails to curtail the illicit drug market may make that market more violent and raise the overall level of violence in societies where drug markets are widespread and endemic. Such warnings are already being taken to heart in parts of Britain's enforcement apparatus where there is acceptance that the aim should be to target the harms drug markets bring with them, not necessarily to target markets per se, and to ensure as far as possible that no new harms are created.

The link the review finds between the level of drug enforcement and the level of violence is enough to warrant such caution because this link might reflect an unwanted impact of enforcement. However, the review falls well short of proving this is the case. Insufficient detail is presented to enable an assessment of how methodologically sound the studies were. Also, the review's explanation of how enforcement as measured in these studies might have caused violence is questionable. It may also be that the type of enforcement is critical – that counterproductive impacts such as violence are limited to traditional police tactics focused on arrests and drug seizures, rather than tactics which target the underlying social and environmental factors which make an area conducive to illicit markets. Similarly, certain types of markets and market players may be more prone to react to enforcement pressure in ways which generate violence. Some may simply retreat in to known and trusted circles. In Britain the tendency is often to avoid attention-attracting and destabilising violence.

A link yes, but did enforcement cause crime?

It is likely that the reviewers analysed the studies in considerable detail, but the published review does not critique each study or indicate the degree to which its methodology was capable of answering the question it addressed. A key issue, for example, is whether a study takes steps to eliminate the possibility that a link between enforcement and violence is due to the stepping up of enforcement to counter an increasing threat from drug-related violence – in other words, to eliminate the possibility that rather than enforcement having caused violence, the reverse was the case. It is big leap from observing that two things vary together to determining which (if either) caused the variation in the other. Making this leap is aided by a plausible explanation or 'mechanism' via which one might affect the other, in this case, an explanation for how increased enforcement might increase violence. The one put forward in the review is that "removing key players from the lucrative illegal drug market ... may have the perverse effect of creating significant financial incentives for other individuals to fill this vacuum". Crackdowns can it suggests disrupt a settled market dominated by a few players and split it in to competing fiefdoms, generating violence in the fight for the spoils. While analysts agree that this can happen, one problem with this explanation is that indices of enforcement intensity in the reviewed studies seem to bear little relation to the removal of key players. Numbers of drug arrests or seizures and spending on enforcement seem at least as likely to reflect generalised enforcement activity which affects drug users and low-level dealers rather than surgical operations targeted at major financiers and organisers.

There are, of course, other explanations for such a link, prime amongst which is that intensified enforcement raises the price of illicit drugs by constricting supply and because dealers raise prices to compensate for heightened risk. In turn, greater rewards lead to greater violence in order to secure those rewards. Such a mechanism is thought to account for the relationship between heroin prices and total or drug-related killings in the USA and several European countries and regions. The prime difficulty with this argument is securing evidence that intensified enforcement has actually led to an increase in price. Indeed, the review highlights the decrease in illicit drug prices in the USA – where most of the studies it reviewed were conducted – as proof that intensified enforcement since the 1990s has not curtailed supply.

The review also notes that the illegality of the market closes off formal dispute-resolution mechanisms like the courts, professional discipline, or reputation-damaging publicity, leaving arguments to be settled by force. While this may be the case, it seems a result of prohibition in itself; it does not explain why the vigour with which it is enforced would influence the extent of resort to force. Yet another possible mechanism is that if police really do focus on what in some countries is a huge illicit drug market, this would significantly detract from the focus on other crimes. Analysis of crime trends suggests this has been the case for property crime in Florida and Portugal; a similar effect may extend to violent crime. Another mechanism is that corruption generated by drug money undermines the effectiveness of enforcement and prevents the imposition of deterrent penalties. Stimulating a defensive 'arms race' is also a well known and counter-productive impact of intensified enforcement which might increase violence if (for example) market participants arm themselves and threaten potential witnesses and informers to avoid capture. Similarly, undercover tactics and the recruitment of informers could undermine trust between market participants and fracture the market in to tight antagonistic cliques which compete rather than cooperate.

Neither should we assume (and the review does not) that drug market participants resort easily and naturally to violence. A small study based on interviews with convicted drug traffickers and law enforcement personnel found this was generally not the case in Britain. As long as those who might countenance violence are making money from a well functioning market, "not only is there no need for violence ... it is to be positively avoided" because it risks police or internal market reactions which are "'bad for business'". The study did however agree that overt as opposed to implied or threatened violence might be a result of market dysfunction and instability. In so far as enforcement contributes to that kind of dysfunction and instability, and if there are no mitigating counter-measures, the effect may be tip the balance from violence being bad for business, to it being seen as a way to retain or incorporate bits of a fragmented market and to regain a kind of fraught stability.

Maybe it depends on the type of enforcement, not just the amount

Possibly the type of enforcement is critical to whether the result is a drug market of much the same size which simply becomes more violent, or a market which – along with related crime – has been sustainably suppressed. Indices of enforcement intensity (such as arrests and seizures) in the reviewed studies seem most likely to reflect traditional policing which reacts to drug markets with 'crackdowns', raids, undercover operations, saturation patrolling and/or stop-and-search policing. Generally these tactics on their own are ineffective, effective only in the short-term, or simply displace the market to other locations or other forms (1 2 3). For a discussion of the benefits and limitations of these approaches see these Findings notes.

But there are other and, from the research, more effective ways to counter illicit markets (1 2). These involve partnerships with community bodies and local people initiated on the basis of an analysis of the underlying problem and intended to alter the social and/or physical environment to make it more resistant to illicit drug markets. Tactics include persuading or forcing landlords to secure and maintain buildings used for drug transactions and to control their tenants, community policing which socially and physically integrates police with the neighbourhood, the mobilisation of local residents and businesses, changing the physical environment by for example eliminating hiding places and removing rubbish and abandoned vehicles, and offering routes out of the market through treatment and reintegration services.

Deploying these or similar tactics alongside conventional law enforcement may mitigate the risk of aggravating violence. Such tactics can also be used to 'secure the ground' cleared by enforcement crackdowns and saturation patrolling. Their impacts are more appropriately measured not in terms of numbers of arrests or seizures, but the improved quality of life of residents and decreased drug-related problems including violent crime. However, implementation involves a much more complex and failure-prone process than straightforward policing, one which requires both the willingness and ability of other groups and services to cooperate – for example, the ability of treatment services to rapidly absorb dependent users who decide to leave an increasingly difficult market.

Maybe it depends on the nature of the market too?

What the review does not (and given the nature of the evidence, may have been unable to) address is whether all types of illicit drug markets are equally likely to become more violent as law enforcement intensifies. For example, 'open' markets which do not rely on sellers and buyers being known to each other have been known to react by becoming more closed. Semi-open (pub- and club-based), closed, 'dealing house', social network and prison-based markets might also respond differently. The drug(s) being marketed may be associated with these different types of markets and different types of market players, so markets in for example, opiates, stimulants, 'dance drugs' or cannabis might also respond differently to enforcement pressure.

Thanks for their comments on this entry in draft to Tim McSweeney of the Institute for Criminal Policy Research at King's College, London, England. Commentators bear no responsibility for the text including the interpretations and any remaining errors.

Last revised 31 March 2011

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