The first Cure Violence project started in 2000, in West Garfield Park in Chicago. Why did they pick that location? ‘It was the most violent police district in the country at the time,’ Slutkin said. ‘It has always been my bias – as it is for many epidemiologists – to head for the middle of the epidemic, because it’s your best test and you can affect the greatest impact.’ One year after the programme started, shootings in West Garfield Park had dropped by about two thirds. The change had been rapid, with interrupters breaking the chains of violence from one person to another. So what is it about these transmission chains that makes interruption possible?
Late on a sunday afternoon in May 2017, two gang members emerged from an alleyway in Chicago’s Brighton Park neighbourhood. They were carrying assault rifles. The pair would end up shooting ten people, killing two of them. It was retaliation for a gang-related murder earlier in the day.[20]
Shootings in Chicago are often linked like this. Andrew Papachristos, a sociologist at Yale University, has spent several years studying patterns of gun violence in the city. A native of Chicago, he’d noticed that shootings were frequently tied to social contacts. Victims would often know each other, having previously been arrested together. Of course, just because two people are connected and share a characteristic – like involvement in a shooting – it doesn’t necessarily mean that contagion is involved. It might be down to the environment they share, or because people tend to associate with those who have similar characteristics (i.e. homophily).[21]
To investigate further, Papachristos and his collaborators obtained data from the Chicago Police Department on everyone who’d been arrested between 2006 and 2014.[22] In total, there were over 462,000 people in the dataset. Using this information, they plotted a ‘co-offending network’ of people who’d previously been arrested at the same time. Many of the individuals hadn’t ever been arrested with someone else, but there was a large group who could be linked together through a series of co-offending events. Overall this group included 138,000 people, or about a third of the dataset.
Papachristos’s team started by checking whether homophily or environmental factors could explain the observed patterns of gun violence. They found that it was unlikely: many shootings occurred in a linked way that couldn’t be explained by homophily or environment, suggesting contagion was responsible. Having identified the shootings that were likely due to contagion, the team carefully reconstructed the chains of transmission between one shooting and the next. They estimated that for every 100 people who were shot, contagion would result in 63 follow-up attacks. In other words, gun violence in Chicago had a reproduction number of about 0.63.
Fifty simulated outbreaks of shootings, based on the dynamics of violence contagion in Chicago. Dots show shootings, with (grey) arrows indicating follow-up attacks. Although there are some superspreading events, most outbreaks involve a single shooting and no onward transmission.
If the reproduction number is below one, it means that an outbreak might spark but it rarely lasts very long. The Yale team identified over four thousand outbreaks of gun violence in Chicago, but most were small. The vast majority consisted of a single shooting, with no additional contagion. However, occasionally the outbreaks were much larger; one included almost five hundred linked shootings. When we see these highly variable outbreak sizes, it suggests that transmission is driven by superspreading events. Analysing the outbreak data from Chicago in more detail, I estimated that transmission of gun violence was highly concentrated. It’s likely that fewer than 10 per cent of shootings led to 80 per cent of follow-up attacks.[23] Just like disease transmission – which can be similarly influenced by superspreading – most shootings didn’t lead to any additional contagion.
The chains of transmission in Chicago also revealed the speed of transmission. On average, the generation time between one shooting and another was 125 days. Despite the attention given to dramatic retaliations like the Brighton Park attack in May 2017, it seems there are a lot of slower-burning feuds out there that have historically gone undetected.
These networks of shootings help explain why the Cure Violence approach is possible. Let’s start with the fact that we can study the networks at all: if we want to control an outbreak, it helps if we can identify potential routes of transmission. Slutkin has compared violence interruption to the methods used to control smallpox outbreaks. As smallpox was nearing eradication in the 1970s, epidemiologists used ‘ring vaccination’ to stamp out the final few sparks of infection. When a new disease case appeared, teams would track down people the infected may have come into contact with, such as family members and neighbours, as well as these people’s contacts. They would then vaccinate people within this ‘ring’, preventing the smallpox virus spreading any further.[24]
Smallpox had two features that worked in health teams’ favour. To spread from one person to another, the disease generally required fairly long face-to-face interactions. This meant teams could identify who was most at risk. In addition, the generation time for smallpox was a couple of weeks; when a new case was reported, teams had enough time to go and vaccinate before more cases appeared. The spread of gun violence shares these features: violence is often transmitted through known social links, and the gap between one shooting and the next is long enough for interrupters to intervene. If shootings were more random, or the gap between them was always much shorter, violence interruption wouldn’t be so effective.
An independent evaluation of Cure Violence by the US National Institute for Justice found a substantial drop in shootings in areas where the programme had been introduced. It can be tough to assess the precise impact of anti-violence programmes, because violence may have already been declining for some other reason. But violence hadn’t declined as much in comparable areas of Chicago, suggesting that Cure Violence was in fact behind the reduction in shootings in many locations. In 2007, Cure Violence started working in Baltimore. When researchers at Johns Hopkins University later assessed the results, they estimated that in its first two years, the programme had prevented around thirty-five shootings and five homicides. Other studies have found similar reductions after the introduction of Cure Violence methods.[25]
Even so, the Cure Violence approach has not been free from criticism. Much of the scepticism has come from those in charge of existing approaches; in the past, there have been complaints from Chicago police about a lack of co-operation from interrupters. There have also been instances of violence interrupters being charged with other crimes. Such challenges are perhaps inevitable, given that the programme relies on having interrupters that are part of the communities at risk, rather than another branch of the police.[26] Then there’s the timescale of social change. While stopping retaliatory attacks can have an immediate effect on violence, tackling the underlying social issues may take years.[27] The same is true with infectious diseases: we might be able to stop outbreaks, but we also need to think about underlying weaknesses in health systems that enabled them in the first place.
Building on their early work in Chicago, Cure Violence has expanded to other US cities, including Los Angeles and New York, as well as launching projects in countries like Iraq and Honduras. Public health approaches would also inspire a ‘Violence Reduction Unit’ in Glasgow, Scotland. Back in 2005, the city was named the murder capital of Europe. There were dozens of knife attacks a week, including numerous incidents of notorious ‘Glasgow smiles’ being slashed into people’s cheeks. What’s more, the violence was far more widespread than police figures suggested. When Karyn McCluskey, head of intelligence analysis at Strathclyde Police, looked at hospital records, it became clear that most incidents weren’t even being reported.[28]
McCluskey’s findings – and accompanying recommendations – led to the creation of the Violence Reduction Unit, which she would head up for the following decade. Borrowing techniques from Cure Violence and other US projects, such as Boston’s Operation Ceasefire, the unit introduced a range of public health ideas to
tackle the spread of violence.[29] This included interruption approaches, like monitoring A&E departments for victims of violence to discourage potential revenge attacks. It also involved helping gang members move into training and employment, while taking a tough stance against those who chose to continue with violence. There were longer-term measures too, like providing support for vulnerable children to halt the transmission of violence from generation to the next. Although there is still more to be done, the initial results have been promising; following its introduction, the unit has been linked with a major drop in violent crime.[30]
Since 2018, London has been working on a similar initiative to tackle what has been described as an ‘epidemic’ of knife crime in the city. If it is to succeed like Glasgow, it will require strong links between police, communities, teachers, health services, social workers, and the media. It will also need continued investment, given the often complex, deep-rooted nature of the problem. ‘It’s about putting money where your mouth is in terms of prevention, and understanding that you may not see a really quick return on it,’ McCluskey told The Independent shortly before the London project launched.[31]
Sustaining investment can be tough for public health approaches. Despite growing acceptance elsewhere, funding for the original Cure Violence programme in Chicago has remained sporadic, with several cutbacks over the years. Slutkin said attitudes to violence are changing in many places, but not as easily as he would hope. ‘It’s frustratingly slow,’ he said.
One of the biggest challenges in public health is convincing people. It’s not just a matter of showing a new approach works better than existing methods. It’s also about advocating for that approach, presenting a compelling argument that can help turn statistical evidence into action.
In the world of public health advocacy, few have been as effective – or as pioneering – as Florence Nightingale. While John Snow was analysing cholera in Soho, Nightingale was surveying the illnesses faced by British troops fighting in the Crimean war. Nightingale had arrived in late 1854 to lead a team of nurses in the military hospitals. She found that soldiers were dying at an astonishing rate. It wasn’t just the fighting that was killing them; it was infections like cholera, typhoid, typhus and dysentery. In fact, infections were the main source of death. During 1854, eight times more soldiers died from diseases than from battle wounds.[32]
Nightingale was convinced poor hygiene was to blame. Each night, she walked over six kilometres along the corridors of the wards, lamp in hand. Patients lay on filthy mattresses, rats hiding beneath, surrounded by walls covered in dirt. ‘The clothes of those men were swarming with lice,’ Nightingale noted, ‘as thick as the letters on a page of print.’ With her nurses, she set about cleaning up the wards. They made sure linens were laundered, bodies bathed, and walls washed. In March 1855, the British government sent a group of commissioners to the Crimea to tackle conditions in the hospitals. Whereas Nightingale had focused on hygiene, the commission worked on the buildings, improving ventilation and sewage systems.
Nightingale’s work earned her fame back at home. Shortly after returning to England in summer 1856, Queen Victoria invited her to come to Balmoral to discuss her experiences in the Crimea. Nightingale used the meeting to push for a Royal Commission to examine the high death rates. What had really happened out there?
As well as contributing to the commission, Nightingale continued with her own research into the hospital data. This work accelerated after she met statistician William Farr at a dinner party that autumn. The two had very different backgrounds: Nightingale came from the upper class, with a name reflecting her childhood in Tuscany, while Farr had been raised in poverty in rural Shropshire, eventually studying medicine before moving into medical statistics.[33]
When it came to population data in the 1850s, Farr was the man to speak to. Alongside his work on outbreaks like smallpox, he had set up the first national system to collate data on things like births and deaths. However, he’d noticed that these raw statistics could be misleading. The total number of deaths in a particular area would depend on how many inhabitants there were, as well as factors like age: a town with an elderly population would generally have more deaths each year than a town full of young people. To solve this problem, Farr came up with a new measurement. Rather than study total deaths, he looked at the rate of death per thousand people, accounting for things like age. It meant he could compare different populations in a fair way. ‘The death-rate is a fact; anything beyond this is an inference,’ as Farr put it.[34]
Working with Farr, Nightingale applied these new methods to data from the Crimea. She showed that death rates in army hospitals were much higher than wards in Britain. She also measured the decline in disease after the health commissioners arrived in 1855. As well as producing tables of data, she took full advantage of a new trend in Victorian science: data visualisation. Economists, geographers and engineers had increasingly used graphs and figures to make their work more accessible. Nightingale adapted these techniques, converting her key results into bar graphs and pie chart-like figures. Like Snow’s maps, the graphics focused on the most important patterns, free of distractions. The visuals were clear and memorable, helping her message to spread.
In 1858, she published her analysis of health in the British Army as an 860-page book. Copies were shipped to leaders ranging from Queen Victoria and the Prime Minister to newspaper editors and European heads of state. Whether looking at hospitals or communities, Nightingale believed that nature followed predictable laws when it came to disease. She said those disastrous early months in Crimea happened because people ignored these laws. ‘Nature is the same everywhere, and never permits her laws to be disregarded with impunity.’ She was also adamant about what had caused the problems. ‘The three things which all but destroyed the army in Crimea were ignorance, incapacity, and useless rules.’[35]
Nightingale’s advocacy sometimes made Farr nervous. He warned her against focusing too heavily on messages rather than data. ‘We do not want impressions,’ he said. ‘We want facts.’[36] Whereas Nightingale wanted to suggest explanations for the cause of the deaths, Farr believed the job of a statistician was simply to report what had happened, rather than speculating about why. ‘You complain that your report would be dry,’ he once told her. ‘The drier the better. Statistics should be the driest of all reading.’
Nightingale used her writing to campaign for change, but she’d never wanted to be just a writer. When she first decided to train as a nurse in the 1840s, it came as a surprise to her wealthy, well-connected family, who’d expected her to pursue the more traditional role of wife and mother. A friend suggested that she could still pursue a literary career alongside this role. Nightingale was not interested. ‘You ask me why I do not write something,’ she replied. ‘I think one’s feelings waste themselves in words; they ought all to be distilled into actions and into actions which bring results.’[37]
When it comes to improving health, actions need to be grounded in good evidence. Today, we routinely use data analysis to show how much health varies, why that might be, and what needs to be done about it. Much of this evidence-based approach can be traced to statisticians like Farr and Nightingale. As she saw it, people generally had little grasp of what controlled infections and what didn’t. In some cases, hospitals may well have increased people’s risk of disease. ‘These institutions, created for the relief of human distress, positively do not know whether they relieve it or not,’ as she put it.[38]
Nightingale’s research was highly respected by her scientific contemporaries, including statistician Karl Pearson. In the public mind, she was the ‘lady with the lamp’, a nurse who cared for soldiers and in turn made people sympathetic to her cause. But Pearson argued that mere sympathy doesn’t lead to change; it requires knowledge of management and administration, as well as an ability to interpret information. He said this was where Nightgale excelled. ‘Florence Nightingale believed – and in all the actions of her life acted
upon that belief – that the administrator could only be successful if he were guided by statistical knowledge.’[39]
According to carl bell, a public health specialist at the University of Chicago, three things are required to stop an epidemic: an evidence base, a method for implementation, and political will.[40] Yet when it comes to gun violence, the US has struggled even with the first step. The US Centers for Disease Control and Prevention (CDC), who would usually take the lead on public health matters, have done very little research into the problem in the past two decades.
Without a doubt, the US is a big outlier when it comes to guns. In 2010, young American adults were almost fifty times more likely to die in a shooting than their peers in other high-income countries. The media tend to focus on mass shootings, which often involve assault weapons, but the problem of gun deaths is far more widespread than this. In 2016, mass shootings – defined as four or more people being shot – made up just 3 per cent of US gun homicides.[41]
So why hasn’t the CDC done more research into gun violence? The main reason is the 1996 Dickey Amendment, which stipulates that ‘none of the funds made available for injury prevention and control at the CDC may be used to advocate or promote gun control.’ Named after Republican congressman Jay Dickey, the amendment followed a series of disagreements about gun research in the US. In the run up to the vote, Dickey and his colleagues had clashed with Mark Rosenberg, director of the National Center for Injury Prevention and Control at the CDC. They claimed that Rosenberg, who co-chaired a firearms working group, was trying to present guns as a ‘public health menace’ (the phrase actually came from a Rolling Stone journalist who’d interviewed Rosenberg about gun violence).[42]
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