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April 27 - May 1, 2020
When there are enough immune people to prevent transmission, we say that the population has acquired ‘herd immunity’. The phrase was originally coined by statistician Major Greenwood in the early twentieth century (Major was his first name, his army rank was actually captain).[36]
Unlike the plain-coloured Anophelines that can fly miles to spread malaria, dengue and Zika are both spread by Aedes mosquitoes, best known for being stripey and lazy (‘aedes’ means ‘house’ in Latin). As a result, the infection generally spreads when humans move from one place to another.[43]
Ross would no doubt be glad to see how influential his ideas have been. Despite winning a Nobel Prize for his discovery that mosquitoes transmit malaria, he did not view this as his biggest achievement. ‘In my own opinion my principal work has been to establish the general laws of epidemics,’ he once wrote.[48] And he didn’t just mean disease epidemics.
CDOs were based on an idea borrowed from the life insurance industry. Insurers had noticed that people were more likely to die following the death of a spouse, a social effect known as ‘broken heart syndrome’. In the mid-1990s, they developed a way to account for this effect when calculating insurance costs.
Others shared her skepticism, viewing popular correlation methods as an overly simplistic way of analysing mortgage products. One leading hedge fund reportedly kept an abacus in one of its conference rooms; there was a label next to it that read ‘correlation model’.[10]
Yet according to Anne Goldgar at Kings College London, there wasn’t really that much of a bulb bubble. She couldn’t find a record of anybody who was ruined by the crash. Only a handful of wealthy people splashed out for the most expensive tulips. The economy was unharmed. Nobody drowned.[16]
Or as comedian John Oliver described it: ‘everything you don’t understand about money combined with everything you don’t understand about computers.’[28]
Then progress stuttered. The obstacle was a 1957 textbook written by mathematician Norman Bailey. Continuing the theme of the preceding years, it was almost entirely theoretical, with hardly any real-life data.
For pandemic flu, R is generally around 1–2, which is about the same as Ebola during the early stages of the 2013–16 West Africa epidemic. On average, each Ebola case passed the virus onto a couple of other people. Other infections can spread more easily. The sars virus, which caused outbreaks in Asia in early 2003, had an R of 2–3. Smallpox, which is still the only human infection that’s been eradicated, had an R of 4–6 in an entirely susceptible population. Chickenpox is slightly higher, with an R around 6–8 if everyone is susceptible.
In 1961, a girl returned from Karachi, Pakistan to Bradford, England, bringing the smallpox virus with her and unwittingly infecting ten other people. An outbreak in Meschede, Germany, in 1969 also started with a visitor to Karachi. This time it was a German electrician who’d travelled there; he would pass the infection on to seventeen others.[50] However, these events weren’t typical: most cases who returned to Europe didn’t infect anyone.
In the sixteenth century, the English believed syphilis came from France, so referred to it as the ‘French pox’. The French, believing it to be from Naples, called it the ‘Neopolitan disease’. In Russia, it was the Polish disease, in Poland it was Turkish, and in Turkey it was Christian.[75]
Two days after lehman went under, Financial Times journalist John Authers visited a Manhattan branch of Citibank during his lunch break. He wanted to move some cash out of his account. Some of his money was covered by government deposit insurance, but only up to a limit; if Citibank collapsed too, he’d lose the rest. He wasn’t the only one who’d had this idea. ‘At Citi, I found a long queue, all well-dressed Wall Streeters,’ he later wrote.[92] ‘They were doing the same as me.’ The bank staff helped him open additional accounts in the name of his wife and children, reducing his risk. Authers
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One sceptic was Lev Landau at the Moscow Institute for Physical Problems. A highly respected physicist, Landau had clear ideas about how much he respected others; he was known to maintain a list rating his fellow researchers. Landau used an inverted scale from 0 to 5. A score of 0 indicated the greatest physicist – a position held only by Newton in the list – and 5 meant ‘mundane’. Landau rated himself a 2.5, upgrading this to a 2 after he won the 1962 Nobel Prize.[4]
As a result, new theories may only gain traction once dominant scientists cede the limelight. As physicist Max Planck supposedly once said, ‘science advances one funeral at a time.’ Researchers at MIT have since tested this famous comment by analysing what happens after the premature deaths of elite scientists.[7] They found that competing groups would subsequently publish more papers – and pick up more citations – while collaborators of the ‘star’ researcher tended to fade in prominence.
Ed Catmull, co-founder of Pixar, has argued that publications are a useful way of building links with specialists outside their company.[8] ‘Publishing may give away ideas, but it keeps us connected with the academic community,’
When researchers at Harvard University used digital trackers to monitor employees at two major companies, they found that the introduction of open-plan offices reduced face-to-face interactions by around 70 per cent. People instead chose to communicate online, with e-mail use increasing by over 50 per cent. Increasing the openness of the offices had decreased the number of meaningful interactions, reducing overall productivity.[10]
Then there was the issue of sexual terminology. ‘There was that mismatch between the public health language and the language of everyday, which was so full of euphemisms,’ Wellings noted. She recalled that several participants didn’t recognise terms like ‘heterosexual’ or ‘vaginal’. ‘All the Latin-sounding names, or any word with more than three syllables, was thought of as something completely weird and unorthodox.’
The most recent Natsal study found that a typical twenty-something in the UK has sex about five times a month on average, with less than one new sexual partner per year.[12] Even the most active individuals are unlikely to sleep with more than a few dozen people in a given year. It means that most interviewees will know how many partners they’ve had and what those partnerships involved.
Hong Kong residents typically have physical contact with around five other people each day; the UK is similar, but in Italy, the average is ten.[15]
As any teacher or parent will know, interactions with children means an increased risk of infection. In the US, people without children in their house typically spend a few weeks of the year infected with viruses; people with one child have an infection for about a third of the year; and those with two children will on average carry viruses more often than not.[19]
otherwise. In the mid-1840s, at the peak of Britain’s railway bubble, engineers assumed that most traffic would come from long-distance travel between big cities. Unfortunately, few bothered to question this assumption. There were some studies on the continent, though. To work out how people might actually travel, Belgian engineer Henri-Guillaume Desart designed the first ever gravity model in 1846. His analysis showed that there would be a lot of demand for local trips, an idea that was ignored by rail operators on the other side of the channel. The British railway network would probably have
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The problem was how to show that smoking was actually causing cancer. Ronald Fisher, a prominent statistician (and heavy pipe smoker) argued that just because the two things were correlated, it didn’t mean one was causing the other. Perhaps smokers had very different lifestyles to non-smokers, and it was one of these differences, rather than smoking, that was causing the deaths?
In 2008, political scientists Brendan Nyhan and Jason Reifler proposed that persuasion can suffer from a ‘backfire effect’. They’d presented people with information that conflicted with their political ideology, such as the lack of weapons of mass destruction in Iraq before the 2003 war, or the decline in revenues following President Bush’s tax cuts. But it didn’t seem to convince many of them. Worse, some people appeared to become more confident in their existing beliefs after seeing the new information.[55] Similar effects had come up in other psychological studies over the years.
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Antonio García Martínez, who spent two years working in Facebook’s ads team, recalled such a situation in his book Chaos Monkeys. Martínez tells the story of a senior manager who built a reputation with pithy, memorable insights about social influence. Unfortunately for the manager, these claims were undermined by research from his company’s own data science team, whose rigorous analysis had shown something different.
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
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‘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.’
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
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.
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.
In 1998, the UK switched from selling paracetamol in bottles to blister packs containing up to thirty-two tablets. The extra effort involved with blister packs seemed to deter people; in the decade after the packs were introduced, there was about a 40 per cent reduction in deaths from paracetamol overdoses.
Rather than ignore results, people may have too much faith in them. Opaque and difficult is seen as a good thing. I’ve often heard people suggest that a piece of maths is brilliant because nobody can understand it. In their view, complicated means clever. According to statistician George Box, it’s not just observers who can be seduced by mathematical analysis. ‘Statisticians, like artists, have the bad habit of falling in love with their models,’ he supposedly once said.[72]
Unfortunately, it’s hard to track drug overdoses because it takes especially long to certify deaths as drug-related. Preliminary estimates for US overdose deaths in 2018 weren’t released until July 2019.
During the Ebola epidemic in Liberia in August 2014, one dataset we were working with suggested that the number of new cases was leveling off in the capital Monrovia. At first this seemed like good news, but then we realised what was actually happening. The dataset was coming from a treatment unit that had reached capacity.
Successful crime reduction can come in a variety of forms. In 1980, for example, West Germany made it mandatory for motorcyclists to wear helmets. Over the next six years, motorcycle thefts fell by two thirds. The reason was simple: inconvenience. Thieves could no longer decide to steal a motorcycle on the spur of the moment.
In 2003, Watts and his colleagues at Columbia re-ran Milgram’s experiment, this time with e-mails and on a much larger scale.[5] Picking eighteen different target individuals across thirteen countries, the team started almost 25,000 e-mail chains, asking each participant to get their message to a specific target.
Watts and his colleagues looked at how web links propagate on Twitter. The results suggested that content was more likely to spread widely if it was posted by a person with lots of followers or a history of making things take off. Yet it was no guarantee: most of the time these people weren’t successful at creating large outbreaks.
For example, in 2012 Sinan Aral and Dylan Walker studied how a person’s friends influenced their choice of apps on Facebook. They found that within friendship pairings, women influenced men at a 45 per cent higher rate than they influenced other women, and over-30s were 50 per cent more influential than under-18s. They also showed that women were less susceptible to influence than men and married people were less susceptible than singles.
From political stances to conspiracy theories, social media communities frequently cluster around similar worldviews.[12] This creates the potential for ‘echo chambers’, in which people rarely hear views that contradict their own.
In 1759, mathematician Daniel Bernoulli decided to try and settle the debate. To work out whether the risk of smallpox infection outweighed the risk from variolation, he developed the first-ever outbreak model. Based on patterns of smallpox transmission, he estimated that variolation would increase life expectancy so long as the risk of death from the procedure was below 10 per cent, which it was.
Users were also far more likely to click on posts that appeared at the top of their feed, showing how intensely content has to compete for attention. This suggests that if echo chambers exist on Facebook, they start with our friendship choices but can then be exaggerated by the News Feed algorithm.[23]
Although ‘trolling’ has become a broad term for online abuse, in early internet culture a troll was mischievous rather than hateful.[28] The aim was to provoke a sincere reaction to an implausible situation. Many of Jonah Peretti’s pre-BuzzFeed experiments used this approach, running a series of online pranks to attract attention.
Analysing the resulting cascade sizes, they found that the content of the tweet itself provides very little information about whether it would be popular. As with their earlier analysis of influencers, the team found that a user’s past tweeting success was far more important. Even so, their overall prediction ability was fairly limited.
When Justin Cheng and his colleagues analysed sharing of photos on Facebook in 2014, they found that their predictions got much better once they had some data on the initial cascade dynamics. Large cascades tended to show broadcast-like spread early on, picking up lots of attention quickly.
Whereas we might adopt a political stance if lots of our friends do, we’re less likely to pick it up from a single source.
Metrics have even shaped literature. When Alexandre Dumas first wrote The Three Musketeers in serialised form, his publisher paid him by the line. Dumas therefore added the servant character Grimaud, who spoke in short sentences, to stretch out the text (then killed him off when the publisher said that short lines didn’t count).[75]
As they pieced together the censorship mechanisms, they discovered that criticism of leaders or policies wasn’t blocked, but discussions of protests or rallies were. Roberts would later divide online censorship strategies into what she calls the ‘three Fs’: flooding, fear, and friction. By flooding online platforms with the opposing views, censors can drown out other messages.
Brendan Nyhan and his colleagues found that although some US voters consumed a lot of news from dubious websites, these people were in the minority. On average, only 3 per cent of the articles that people viewed were published by websites peddling false stories. They later published a follow-up analysis of the 2018 midterms; the results suggested that dodgy news had an even smaller reach during this election. In the UK, there was also little evidence of Russian content dominating conversations on Twitter or YouTube in the run up to the eu referendum.[101]
The first ever computer virus to spread ‘in the wild’ outside of a laboratory network started as a practical joke. In February 1982, Rich Skrenta wrote a virus that targeted Apple II home computers. A fifteen-year-old high school student in Pennsylvania, Skrenta had designed the virus to be annoying rather than harmful.
According to journalist Fred Kaplan, Russian intelligence had supplied infected USB sticks to several shopping kiosks near the nato headquarters in Kabul. Eventually an American soldier had bought one and used it with a secure computer.
When outbreaks are driven by superspreading events, it makes the transmission process extremely fragile. Unless an infection hits a major hub, it probably won’t go very
