Tim Harford The Undercover Economist

Articles published in November, 2012

The random side of riots

We talk as if we understand why civil disorder happens, rather than recognising the unpredictable processes at play

Around this time last year, I stood at the threshold of my home in Hackney, with a week-old baby asleep inside and two helicopters overhead tracking the looters outside. As far as I could figure out there was trouble about 100m to the south, and more trouble about 300m to the north. I didn’t venture far, I’m afraid; my paternal instincts were stronger than my journalistic ones.

A neighbour, holidaying in Scotland, called to advise me to get my family out of London. He was concerned that civilisation was about to collapse. I wasn’t, but I admit that during those bizarre few days it didn’t seem absurd to entertain the possibility.

Why did the riots happen? Every pundit had an explanation, from government cuts to soft policing. But there’s a very different way to look at last summer.

Consider the following simple model of a potential riot, based on an idea published in 1978 by the sociologist Mark Granovetter. There are 1,000 people in a crowd of protesters, and all of them have some underlying tendency to embark on a looting spree. We might reckon that an outbreak of rioting might be triggered by insensitive policing, or by the poverty of the crowd, or the opportunities for theft or for violent protest. But for simplicity let’s assume that the only thing everyone in the crowd cares about is what everyone else in the crowd is doing. Some people will start looting without much company. Others will hang back until the riot is well under way.

Let’s put a number on this riotous tendency. One anarchic lunatic has a threshold of zero: he requires nobody else’s encouragement to start throwing bricks at the police. Another person has a threshold of one: he needs someone else to get things kicked off, but then he’s happy to join in. Then there’s a person with a threshold of two and another with a threshold of three, all the way up to the wallflower of the crowd who has a threshold of 999 – he’ll join in only when there’s literally nobody else standing back.

As you no doubt appreciate, this crowd will display a domino-like tendency to riot: the first person encourages the second; that pair draws in a third; then a fourth and a fifth, until everyone is on the tear.

An interesting lesson quickly emerges from this simplistic model. Imagine that, say, the fourth person in an otherwise identical crowd doesn’t have a threshold of three but of four. This second crowd will behave itself: after the first two troublemakers start acting up, there is no third person willing to join them. The outcomes could hardly be more different – and certainly there would have been no national and indeed international media frenzy if the 2011 riots had consisted of two yobs causing trouble on the fringes of a protest in Tottenham, and nobody else joining in.

Yet we know, because we constructed the examples, that these utterly different results emerged from all but indistinguishable initial conditions. One person out of 1,000 had a fractionally different inclination to riot (by one-tenth of 1 per cent of the observed range). As Duncan Watts points out in his book Everything Is Obvious Once You Know the Answer, the two crowds would seem identical to any survey or statistical test you might care to deploy. The same tendency for apparently identical conditions to produce utterly different outcomes also appears in field experiments carried out by Duncan Watts, and in recent models based on more realistic networks of influence.

Nevertheless, we persist in talking as though we understand why riots happen, rather than recognising the random self-reinforcing processes at play. Social influence can work that way. Last year it was arson and assault across English cities. This year it is buying Fifty Shades of Grey.

Also published at ft.com.

Unloading the dice on research

A compulsory register of trials could give a more accurate view of studies and test results

I just rolled a six-sided die a few times. I rolled: six, five, five, six, five. My question is: do you think the die is biased? One way to think about that question is to ask how likely I would be to roll only fives and sixes completely by chance. Not that likely: the odds are 242 to 1 against.

Before you conclude that I have crooked dice, let me mention something that had slipped my mind. As well as those fives and sixes, I also rolled four, three, three, three, two, two and one. But those results just didn’t seem that interesting, so I didn’t tell you about them. If that omission seems relevant, you’re beginning to appreciate the importance of the nerdy-sounding “trial register”.

Every day, across the world, researchers are conducting randomised controlled trials (RCTs). Some are rigorous, painstaking quests for truth, while others may cut a few corners in the search for a career-defining publication, or a licence for a new drug compound. But even if each individual trial was unimpeachable, the results would mean very little if there was a systematic bias in favour of a particular kind of result.

I reported my die-rolling with a bias towards high numbers. You might uncharitably suspect that an industry-sponsored drug trial would be more likely to see the light of day if the results show that the drug works, and you would be correct (a state of affairs ably summarised by Ben Goldacre in his new book Bad Pharma). Trials can also go missing because they end in chaos or disaster: such stories may not be worth an academic paper but they must be recorded. And trials go missing because the results are so boring that the researchers cannot bring themselves to write them up properly for publication.

As my die-rolling shows, unless we see every trial that was begun, we have a distorted picture of what is happening. There is probably only one way to achieve that goal: a compulsory register of trials. Researchers who conduct trials and abandon them or don’t publish, need to become pariahs. Systematic reviews of a particular field will be able to consult the registers and track down any unpublished trials.

A few years ago, the International Committee of Medical Journal Editors announced that the prestigious journals under its control would no longer publish research based on clinical trials unless those trials had been formally registered before they began. This had the very welcome effect of increasing, dramatically, the number of registered trials and the rate at which new trials were registered. Unfortunately, as Sylvain Mathieu and others explained in the Journal of the American Medical Association in 2009, more than half the research they examined flouted that rule and was published anyway. The threat not to publish seems to have been empty.

And what of economics, which has in recent years discovered the joys of randomised trials? There is good news: the American Economic Association is creating a trial register for trials in economics; it is due to be up and running next year. The register will be voluntary for now, but two leading practitioners, Esther Duflo of MIT and Dean Karlan of Yale, both told me they are hopeful that a strong social norm will form in favour of registering trials. We shall see.

Trial registries are a particular challenge in the social sciences. While an RCT in medicine is designed to test whether a specific treatment does or does not work, in the social sciences they are more likely to be used to search for interesting hypotheses. Social science RCTs are often partnerships between academics and practical organisations, and the trial may evolve over time in a way that a clinical trial would not.

All this complicates the business of registering the trial and then updating the entry as things change. It makes a trial registry harder to maintain. But it also makes the registry even more essential.

Also published at ft.com.

A battle for our green and pleasant land

‘There has been no change in the government’s policy on renewable energy, the prime minister has said.’ – BBC News

That’s news?

That is news because it follows hard on the heels of a declaration by John Hayes, the new energy minister, that “enough is enough” as far as onshore wind farms are concerned.

That sounds like a change in the government’s energy policy.

It does indeed. The number of wind farms has been growing steadily, and RenewableUK, the industry body, recently announced that approvals for new onshore wind farms were up for the first time in five years, and sharply so. Mr Hayes, in contrast, was quoted as saying: “I can’t single-handedly build a new Jerusalem but I can protect our green and pleasant land.”

I’m guessing he’s a Tory rather than a Liberal Democrat, somehow.

Given the new Jerusalem reference, I am starting to suspect that Mr Hayes is not a Conservative but instead a comic actor taking the role of a Tory MP and playing it for laughs. Officially Mr Hayes is a Conservative but his boss, Ed Davey, is a Lib Dem and Mr Davey was quick to overrule Mr Hayes.

But what was Mr Hayes planning to do, then, before he was overruled?

He was planning to commission new evidence on which to base his future “enough is enough” policy, suggesting that the existing policy wasn’t based on evidence but on a “bourgeois left article of faith based on some academic perspective”.

I’m confused. How does he know what the new evidence will say before he’s seen it?

It is odd. Mr Hayes is not the only politician to rely on clairvoyant evidence, as the science writer Mark Henderson has pointed out. Politicians have a habit of announcing what the research will discover before the research has been carried out. Scientists, rather quaintly, undertake research because they don’t know what the results will be.

Oh, those pesky scientists. Don’t worry about them. They have an academic perspective, I think you will find.

Apparently so.

So what is the situation with wind power, then?

For a windy country, the UK’s installed capacity is middling at best. In Europe, its capacity is just behind that of Italy and France but dwarfed by Spain and Germany. But Mr Hayes may have reason to be more worried about recent trends: in 2011, the UK installed more capacity than any European country other than Germany.

What about offshore wind? Surely that is no threat to the new Jerusalem.

According to RenewableUK, the UK has more offshore wind capacity installed than the rest of the world put together.

Splendid news!

I wouldn’t be so sure about that. Renewable energy requires substantial subsidy. Why do we subsidise it? Chiefly because of climate change and perhaps because of the fear that fossil fuels will eventually run out. But these issues are both global and long-term, which means that what really matters is to develop technologies that have a chance of being adopted across the world.

And we’re a global leader in offshore wind farms.

I fear that we may remain a global leader in offshore wind farms because so few other countries are interested in the technology, which is an expensive way to pander to the tastes of small, rich coastal areas. I wonder if wind farms optimised for the plains of Mexico or the steppes of Mongolia might be a better bet than trying to figure out how to plant windmills in the Irish Sea and keep them from corroding.

You seem rather cynical about the whole thing.

I am. Climate change is no joke and dealing with it is going to require some big technological leaps. We need a substantial and credible carbon price and a far more radical scheme of funding low-carbon innovation. Instead we have an ugly game of political football. The spat between Mr Hayes and Mr Davey will make renewable energy providers nervous and make it even more expensive for the taxpayer to persuade them to make risky investments.

Do you want these investments or don’t you?

I suspect that the future of low-carbon technology is going to involve a lot more nuclear and geothermal energy and a lot less wind. But I am probably wrong; nobody knows. I am sure of this: it’s expensive enough to build wind farms already without stirring up uncertainty and then having to pay danger money just to persuade investors to brave our shambolic energy policy.

Also published at ft.com.



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