The Rules of Contagion

by Adam Kucharski

  That’s if we even think about different arguments. A few years ago, social psychologists Matthew Feinberg and Robb Willer asked people to come up with arguments that would persuade someone with an opposing political view. They found that many people used arguments that matched their own moral position, rather than the position of the person they were trying to persuade. Liberals tried to appeal to values like equality and social justice, while conservatives based their argument on things like loyalty and respect for authority. Arguing on familiar ground might have been a common strategy, but it wasn’t an effective one; people were far more persuasive when they tailored their argument to the moral values of their opponent. This suggests that if you want to persuade a conservative, you’re better off focusing on ideas like patriotism and community, whereas a liberal will be more convinced by messages promoting fairness.[68]

  Even if you manage to identify an effective argument to support your position, there are things you can do to improve your chances of persuasion. First, the delivery method can matter. There’s evidence that people are much more likely to complete a survey if asked in person rather than by e-mail,[69] for example. Other experiments have come to similar conclusions, finding that people can be more convincing face-to-face than by phone, post or online.[70]

  The timing of messages can also make a difference. According to Briony Swire-Thompson, a psychologist at Northeastern University, researchers are increasingly thinking about how ideas wane. ‘It’s this concept that once you change someone’s mind, it doesn’t stick permanently.’ In 2017, she conducted a study asking people whether they believed certain myths, like carrots improving your eyesight or liars moving their eyes in a certain direction.[71] The study found that they could often correct false beliefs, but the effect didn’t necessarily last. ‘If you get a correction, you might reduce your belief initially, but as time goes on you’re going to re-believe in the initial misconception,’ Swire-Thompson said. It seems repetition matters: new beliefs survived longer if people were reminded of the truth several times, rather than just given one correction.[72]

  Thinking about the moral position of others. Having face-to-face interactions. Finding ways to encourage long-term change. All of these things can help improve persuasion. And it happens that they are also part of the deep canvassing approach advocated by the Los Angeles LGBT Center. Which brings us back to that dubious LaCour and Green paper. Although the study was retracted in 2015, the story didn’t end there. The following year, David Brookman and Joshua Kalla – those two Berkeley researchers who’d found the problems in the original paper – published a new study.[73] This one focused on transgender rights. And this time they’d definitely collected the data.

  Comparing deep canvassing with results from a control group, they’d found that a ten-minute conversation about transgender rights could noticeably reduce prejudice. It didn’t matter whether the canvasser was transgender; the change in voters’ opinion persisted regardless. The change in belief also seemed to be resistant to attacks. After a few weeks, the researchers showed people anti-transgender adverts from recent political campaigns. The ads initially swung opinions back against transgender people, but this reversion effect soon faded.

  To ensure the research was completely transparent, Brookman and Kalla published all the data and code behind the analysis. It provided an optimistic epilogue to what had been an awkward few years for the research community. With the right approach, it was possible to change attitudes that many had believed were deeply ingrained. It showed that views don’t necessarily spread in the way we assume they do, nor are people as fixed as we think they might be. When faced with apparent hostility, it seems there can be a lot to gain by trying something new.

  4

  Something in the air

  ‘We were in a place with real violence.’ After a decade spent working on disease epidemics in Central and East Africa, Gary Slutkin had returned home to the United States. He’d chosen Chicago to be near his elderly parents and was struck by the extent of violent attacks in the city. ‘It was surrounding, it was inescapable and so I just started to ask people what they were doing about it,’ Slutkin said. ‘And there wasn’t anything that anybody was doing about this that made any sense to me.’[1]

  It was 1994 and in the preceding year, there had been over eight hundred homicides in the city, including sixty-two children killed in gang violence. Even two decades later, homicide would still be the main cause of death for young adults in the state of Illinois.[2] Slutkin heard a range of explanations for the crisis, from nutrition and jobs to families and poverty. But the discussions often came back to a narrow set of solutions involving punishment. In his view, violence was what he called a ‘stuck problem’. A physician by training, he’d seen similar situations in his work with infectious diseases like hiv/aids and cholera. Sometimes the thinking about a situation gets stuck for years. A strategy doesn’t really work, but it doesn’t change.

  If violence were a stuck problem, it would need new thinking. ‘You have to kind of start over,’ Slutkin said. So he did what any public health researcher would do: he looked at maps and graphs, he asked questions, he tried to understand how violence was happening. And that’s when he started noticing familiar patterns. ‘The clustering seen in maps of killings in US cities resembles maps of cholera in Bangladesh,’ he later wrote.[3] ‘Historical graphs showing outbreaks of killing in Rwanda resembled graphs of cholera in Somalia.’

  Susannah eley liked to get her water delivered each day. After her husband had died, she’d moved from the bustle of London’s Soho to leafy Hampstead. But she still preferred the water from the pump in town. She thought it tasted better.

  One August day in 1854, Eley’s niece visited her from the neighbouring borough of Islington. Within a week, they would both be dead. The culprit was cholera, an aggressive disease that causes diarrhea and vomiting. Left untreated, up to half of people with severe symptoms will die. The same day that Eley died from cholera, there were 127 other deaths from the disease, most of them in Soho. By the end of September, the outbreak would have claimed over six hundred lives in London. In this era before Koch’s work on germ theory, the biology of cholera was still a mystery. ‘We know nothing; we are at sea in a whirlpool of conjecture,’ wrote Thomas Wakley, founder of The Lancet medical journal, the year before the outbreak started. People were starting to realise that diseases like smallpox and measles were contagious, somehow spreading from person to person, but cholera seemed to be something else. Most believed the ‘miasma theory’, which said that cholera spread through bad smells in the air.[4]

  But not John Snow. Originally from Newcastle, Snow had investigated his first cholera outbreak in 1831 as an eighteen-year-old medical apprentice. Even then, he’d noticed some odd patterns. People who should have been at risk from bad air weren’t getting ill, and people who supposedly weren’t at risk were. Snow eventually moved to London, building up a reputation as a talented anaesthetist, with Queen Victoria among his patients. However, when a cholera outbreak hit the city in 1848, he revived his old investigations. Who was catching the disease? When were they getting ill? What linked the cases? The following year, Snow published an article with a new theory: the disease spread from one person to another through contaminated water. The realisation had finally come when he noticed that patients would often share the same water company. It was a remarkable insight, not least because Snow had no idea it was actually microscopic bacteria that were casting cholera’s enormous shadow.

  The 1854 Soho outbreak would prove a good match for Snow’s theory. There were the workers at the local brewery, with their diet of ale and imported water, who didn’t get sick. Then there was Susannah Eley and her niece, who had their water shipped from Soho to Hampstead and fell ill. As the outbreak grew, Snow decided it was time to intervene. Public health in Soho fell under the responsibility of a local Board of Guardians. He turned up uninvited at one of their meetings and presented his arguments. The board didn’
t fully believe his explanation, but decided to remove the pump handle all the same. The outbreak ended soon afterward.

  Three months later, Snow wrote up his theory in more detail. The report included what would become his most famous illustration: a map of Soho, with black rectangles showing each of the cholera cases. The cases clustered around Broad Street, near the pump. It was a pioneering work of abstraction, removing unnecessary details and diversions. Whereas abstract artists like Malevich and Mondrian would later paint blocks of colour to shun reality, Snow’s shapes brought cholera into focus.[5] His rectangles made a previously invisible truth – the source of infection – tangible.

  Snow’s updated cholera map of Soho

  Credit: John Snow Archive & Research Companion. The mark on the right-hand side is a tear in the original page

  Yet on its own, the map was not clear evidence that the water was responsible. If the cholera outbreak had been the result of bad air around Broad Street, the pattern would have looked much the same. So Snow produced a second map, with a crucial addition. As well as plotting the cases, he worked out how long it would take to walk to different pumps, drawing a line to show the places for which the Broad Street pump was nearest. It illustrated the areas that would be most at risk if the pump were to blame. Just as his theory suggested, this was also where most cases were appearing.

  Snow would never live to see his ideas vindicated. When he died in 1858, The Lancet published a two-sentence obituary, which failed to mention his work on outbreaks. Like an intellectual miasma, the concept of bad air continued to linger in the medical community.

  Eventually the idea of contagious cholera did catch on. By the early 1890s, many had come to accept Robert Koch’s notion of germs that spread disease. Then, in 1895, Koch managed to infect a laboratory animal with cholera.[6] His postulates fulfilled, it was convincing evidence that bacteria was causing the disease, and that cholera was spreading through infected water rather than coming from bad air. Snow had been right.

  We now think about infectious diseases in terms of germs rather than miasma, but Gary Slutkin argues that we haven’t made the same progress in our analysis of violence. ‘We’re very stuck in moralism – who’s good, who’s bad.’ He points out that many societies are highly punitive; they haven’t really shifted in their attitudes to violence for centuries. ‘I really feel like I’m living in the past.’

  Although biology has moved on from the idea of bad air, debate around crime still focuses on bad people. Slutkin thinks this is in part because contagious violence is less intuitive than disease. ‘Here you don’t actually have an invisible microorganism that you can at least show somebody under the microscope.’ However, the parallels between infectious disease and violence seemed clear to him. ‘I remember an epiphany when I asked someone “what’s the greatest determinant of violence? What’s the greatest predictor?” And the answer was “a preceding violent event”.’ In his mind, it was an obvious sign of contagion. Which made him wonder: perhaps methods used to control infectious diseases could be applied to violence too?

  There are several similarities between outbreaks of disease and violence. One is the lag between exposure and symptoms. Just like an infection, violence can have an incubation period; we might not see symptoms straight away. Sometimes a violent event will lead to another one soon after: for example, it might not take long for one gang to retaliate against another. On other occasions it may take much longer for knock-on effects to emerge. In the mid-1990s, epidemiologist Charlotte Watts worked with the World Health Organization (who) to set up a major study of domestic violence against women.[7] Watts had trained as a mathematician before moving into disease research, focusing on hiv. As her work on hiv developed, she started to notice that violence against women was influencing disease transmission because it affected their ability to have safe sex. But this revealed a much bigger problem: nobody really knew how common such violence was. ‘Everybody agreed that we needed population data,’ she said.[8]

  The who study was the result of Watts and her colleagues applying public health ideas to the issue of domestic violence. ‘A lot of previous research treated it as a police issue or focused on psychological drivers of violence,’ she said. ‘Public health people ask, “What’s the big picture? What does the evidence say about individual, relationship and community risk factors?”’ Some have suggested that domestic violence is completely context or culture specific, but this isn’t necessarily the case. ‘There are some really common elements that consistently come out,’ Watts said, ‘like exposure to violence in childhood.’

  In most of the locations in the who study, at least one in four women had previously been physically abused by a partner. Watts has noted that violence can follow what’s known in medicine as a ‘dose-response effect’. For some diseases, the risk of illness can depend on the dose of pathogen a person is exposed to, with a small dose less likely to cause severe illness. There’s evidence of a similar effect in relationships. If a man or woman has a history involving violence, it increases the chance of domestic violence in their future relationships. And if both members of the relationship have a history of violence, this risk increases even further. This isn’t to say that people with a history involving violence will always have a violent future; like many infections, exposure to violence won’t necessarily lead to symptoms later on. But like infectious diseases, there are a number of factors – in our backgrounds, in our lifestyles, in our social interactions – that can increase the risk of an outbreak.[9]

  Another notable feature of disease outbreaks is that cases tend to cluster together in a certain location, with infections appearing over a short period of time. Think about that cholera outbreak in Broad Street, with cases clustered around the pump. We can find similar patterns when looking at violent acts. For centuries, people have reported localised clusters of self-harm and suicide: in schools, in prisons, in communities.[10] However, clustering of suicides doesn’t necessarily mean contagion is happening.[11] As we saw with social contagion, people may behave in the same way for another reason, like some shared feature of their environment. One way to exclude this possibility is to look at the aftermath of high-profile deaths; a member of the public is more likely to hear about the suicide of a well-known person than the other way around. In 1974, David Phillips published a landmark paper examining media coverage of suicides. He found that when British and American newspapers ran a front-page story about a suicide, the number of such deaths in the local area tended to increase immediately afterwards.[12] Subsequent studies have found similar patterns with media reports, suggesting that suicide can be transmitted.[13] In response, who have published guidelines for responsible reporting of suicides. Media outlets should provide information about where to seek help, while avoiding sensational headlines, details about the method involved, and suggestions that the suicide was a solution to a problem.

  Unfortunately, outlets often ignore these guidelines. Researchers at Columbia University noted a 10 per cent rise in suicides in the months following the death of comedian Robin Williams.[14] They pointed to a potential contagion effect, given that many media reports about Williams’ death did not follow who guidelines, and the largest increase in suicides occurred in middle-aged men using the same method as Williams. There can be a similar effect with mass shootings; one study estimated that for every ten US mass shootings, there are two additional shootings as a result of social contagion.[15]

  Because there is often an immediate rise in suicides and shootings following such media reports, it suggests that the delay between one contagious event and another – known in epidemiology as the ‘generation time’ – is relatively short. Some clusters of suicides have involved multiple deaths over a matter of weeks: in 1989 there was an outbreak of suicides at a Pennsylvania high school, which saw nine attempts in eighteen days. If these events were the result of contagion, the generation time may in some cases have been only a few days.[16]

  Clustering is common with
other types of violence too. In 2015, a quarter of US gun murders were concentrated in neighborhoods that made up less than 2 per cent of the country’s overall population.[17] When Gary Slutkin and his colleagues set out to tackle violence as if it were an outbreak, it was neighbourhoods like these that they planned to target. They called the initial programme ‘CeaseFire’; this would later evolve into a larger organisation called Cure Violence. In those early days, it took a while to work out precisely what approach they should use. ‘We took five years of strategy development before we put a single thing on the street,’ Slutkin said. The Cure Violence method would end up having three parts. First, the team hires ‘violence interrupters’ who can spot potential conflicts and intervene to stop the transmission of violence. Someone might end up in hospital with a gunshot wound, for example, and an interrupter will step in to talk their friends out of a retaliatory attack. Second, Cure Violence identifies who is at greatest risk of violence, using outreach workers to encourage a change in attitudes and behaviour. This can include help with things like job hunting or drug treatment. Finally, the team works to change social norms about guns in the wider community. The idea is to have a range of voices speaking out against a culture of violence.

  Interrupters and outreach workers are recruited directly from the affected communities; some are former criminals or gang members. ‘We hire workers who are credible with that population,’ said Charlie Ransford, Cure Violence’s Director of Science and Policy. ‘To change people’s behaviour and talk them out of doing something it helps if you have an understanding of where they’re coming from, and they feel like you have an understanding and maybe even know you or know someone who knows you.’[18] This is another idea familiar in the world of infectious diseases: hiv programs will often recruit former sex workers to help change behaviour among workers who are still at high risk.[19]