Lawrence Sherman and the Invention of Evidence-Based Policing

In 1981 a criminologist talked the Minneapolis police into running their domestic violence calls as a scientific experiment. When officers reached a misdemeanour assault with both parties still on the scene, a pad of colour-coded report forms told them, at random, which of three responses to use: arrest the suspect, send one party away for the night, or give advice and leave. The aim was to find out, rather than guess, which response did most to stop the violence happening again.

The man behind the pad of random assignments was Lawrence W. Sherman, and the study — the Minneapolis Domestic Violence Experiment — was the first randomised controlled trial ever run on the effect of arrest. Readers of the profile of Alex Murray will know the name already: Sherman is the American academic who taught Murray at Cambridge and whose framework Murray carried back into British policing. This is the story of the scientist himself, and of the idea he spent fifty years pressing on a profession that did not, at first, want to hear it: that the police should be tested like medicine.

The police should be tested like medicine.

The making of an experimentalist

Sherman was born in 1949 and educated on both sides of the Atlantic. He took a degree in political science at Denison University in Ohio, a master’s at the University of Chicago, a diploma in criminology at Cambridge in 1973, and finally a doctorate in sociology at Yale in 1976. The Cambridge year mattered: it gave an American sociologist a lasting tie to the English institution he would eventually lead, and to a tradition of careful, quantitative criminology.

His first home as a researcher was the Police Foundation in Washington, where he became director of research. The Foundation had already run the Kansas City Preventive Patrol Experiment in the early 1970s, which found that varying the amount of routine patrol made no measurable difference to crime or to public fear. That result — that one of policing’s central activities might simply not work the way everyone assumed — seems to have set the course of Sherman’s career. If patrol could be tested and found wanting, so could anything. The question was whether the police would let it be tested.

The experiment that changed the law, and then complicated it

In Minneapolis they let him. The headline finding was striking: arrest roughly halved the rate of repeat offending compared with the softer responses. It travelled fast. Within a few years some 28 US states had rewritten their domestic violence laws to favour or require arrest, and the experiment became one of the clearest cases on record of a single study moving statute.

What happened next is the part that matters most for understanding Sherman, and the reason his name belongs at the head of this field rather than merely in it. The result was important enough that the National Institute of Justice paid for it to be repeated in six other cities. The tidy Minneapolis finding did not hold. In several replications arrest made no difference, and in Milwaukee Sherman found something worse: among suspects who were unemployed, arrest appeared to increase later violence. The policy the first experiment had inspired — mandatory arrest — looked, on fuller evidence, as if it might be harming some of the very people it was meant to protect.

A lesser researcher might have buried that. Sherman published it, wrote a book reckoning with it, and used it for the rest of his career as the central lesson of the whole enterprise. An experiment that tells you your earlier conclusion was wrong has not failed. It has done the one thing that distinguishes science from advocacy. Murray, his student, would later put the same thought in plainer words: failure is a good thing, including trying to evaluate something and finding that you cannot. He learned it, in part, here.

Crime has an address

Sherman’s second great contribution was to ask not what works but where. Analysing a year of calls to the Minneapolis police in the late 1980s with Patrick Gartin and Michael Buerger, he found that crime was not spread evenly across a city at all. It clustered, and the clustering was extreme.

Just 3.5% of the city’s addresses produced half of all the calls to police. The finding has been reproduced in city after city since, and it is the empirical foundation of what became known as hot-spots policing. If most harm comes from a few places, then patrol aimed at those places should do more good than patrol spread thin everywhere. Sherman and David Weisburd tested exactly that in the Minneapolis Hot Spots Experiment, randomly assigning extra patrol to some high-crime corners and not others, and found that the targeted corners saw less crime and disorder. A later Kansas City study showed that concentrated patrol and gun seizures in a single violent neighbourhood cut gun crime there. Place, it turned out, was something the police could act on with evidence behind them.

Naming the idea

By 1998 Sherman had a body of experiments and a conviction about what they meant, and he gave the conviction a name. In a lecture for the Police Foundation, published as a short paper that has been cited ever since, he set out the concept of evidence-based policing. The phrase was a deliberate echo of evidence-based medicine, then transforming clinical practice, and the argument was the same: that practitioners should be guided by the best available research about what actually works, not by custom, intuition or rank.

He later sharpened the framework into a slogan that British readers may recognise from the Murray profile. For most of its history, Sherman argued, policing had run on three Rs — random patrol, rapid response and reactive investigation — none of which had much evidence behind it. In their place he proposed the Triple-T: targeting the few places, times and people that cause most harm; testing responses through controlled trials; and tracking whether the effect lasts. The framework is set out in full, with a diagram, in the Murray piece; the point worth making here is whose framework it was. Murray built the institution. Sherman built the idea it was founded to spread.

Cambridge, and a school of officers

Sherman’s American career was substantial in its own right. He chaired the criminology department at the University of Maryland, then moved to the University of Pennsylvania, where in 2003 he founded the first separate department of criminology in the Ivy League. But his lasting influence on British policing runs through Cambridge, where he returned in 2007 as Wolfson Professor of Criminology, later directing the Institute of Criminology and the Jerry Lee Centre of Experimental Criminology.

The vehicle was the Police Executive Programme, the part-time Cambridge master’s for serving senior officers, which from 2008 Sherman built around evidence-based policing. A generation of British and international police leaders passed through it, writing their own small experiments as dissertations and carrying the method home to their forces. Alex Murray’s 2008 thesis on police legitimacy in Muslim communities was one of them; the two later co-authored a peer-reviewed paper from it. The Society of Evidence-Based Policing that Murray founded in 2010 elected Sherman its honorary president. Much of what looks, from the outside, like a British movement was in practice a Cambridge seminar room spreading outward.

Two further pieces of work from this period are worth naming. With Heather Strang, Sherman ran a long programme of randomised trials of restorative justice — bringing offenders and victims face to face — which found, against many expectations, that it often reduced reoffending and helped victims more than conventional prosecution. And in 2016, with the former chief constable Peter Neyroud, he proposed the Cambridge Crime Harm Index: a way of counting crime weighted by the harm each offence does, measured by the sentence the guidelines recommend for it, rather than treating a stolen bicycle and a serious assault as one “crime” apiece. It is a quiet idea with large consequences, because what a police force measures is what it ends up managing.

The honours, and the argument they recognise

The recognition followed. Sherman received the American Society of Criminology’s Edwin Sutherland Award, its highest honour, in 1999, and served as the Society’s president in 2001. Germany’s criminological societies gave him the Beccaria Gold Medal in 2009; the Royal Society of Arts awarded him its Benjamin Franklin Medal in 2011. With the philanthropist Jerry Lee he helped create the Stockholm Prize in Criminology, first awarded in 2006, and has co-chaired its jury since. One ranking of citation influence placed him as the most influential criminologist of the 2010s. The titles matter less than the through-line they trace: a single argument, pressed for half a century, that the police should find out whether what they do works.

What the experiments cannot settle

It would flatter the field to pretend the argument is won, or that it answers every objection. It does not, and the strongest criticisms deserve stating plainly. Experiments do not always replicate — the domestic violence saga is proof of that from inside the discipline. A method built to ask “what works?” can quietly narrow the question to “what reduces recorded crime?”, and crowd out harder questions about what is just, or lawful, or fair to the policed. Hot-spots policing, in particular, concentrates police attention on a small number of places, and the people who live in those places are not evenly distributed across a society; done badly, targeting the map can mean targeting the same communities again and again, at a cost to trust that no crime count captures.

Sherman’s answer was never that evidence settles questions of value. It is that you cannot have a sensible argument about values without first knowing what your choices actually do. The Minneapolis reversal is, in the end, his best case. A profession that arrests because arresting feels like justice will never discover that its instinct is sometimes wrong. A profession that runs the experiment can. That capacity to be corrected by its own findings is not a weakness of evidence-based policing. It is the whole of what Sherman was offering.

The detective who built the Society learned the method from the professor who built the experiment. Between them they moved British policing, slowly and incompletely, towards a harder and more honest standard than the one it inherited: not “this is how we have always done it”, but “show me that it works”.

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Sources and further reading

• Lawrence W. Sherman, “Evidence-Based Policing”, Ideas in American Policing, Police Foundation, 1998.
• Lawrence W. Sherman and Richard A. Berk, “The Minneapolis Domestic Violence Experiment”, Police Foundation, 1984.
• Lawrence W. Sherman, Patrick R. Gartin and Michael E. Buerger, “Hot Spots of Predatory Crime: Routine Activities and the Criminology of Place”, Criminology, 1989.
• Lawrence W. Sherman and David Weisburd, “General Deterrent Effects of Police Patrol in Crime Hot Spots: A Randomized, Controlled Trial”, 1995.
• Lawrence Sherman, Peter Neyroud and Eleanor Neyroud, “The Cambridge Crime Harm Index: Measuring Total Harm from Crime Based on Sentencing Guidelines”, Policing, 2016.
• University of Cambridge, MSt in Applied Criminology and Police Management (Police Executive Programme).
• Cambridge Centre for Evidence-Based Policing, Professor Lawrence W. Sherman.
• Wikipedia, Lawrence W. Sherman, Evidence-based policing and Minneapolis Domestic Violence Experiment.