The risks of imprecision

When being half-right can be worse than being wrong.

Chris Dillow has a nice post up, "in praise of imprecision". He argues that, in far too many situations, we argue over tiny differences in estimates when the overall answer is basically known. What's GDP growth for last year? It's basically flat. Yet for all the arguments, you would think that the difference between -0.3 and -0.1 per cent – or even between -0.1 and 0.1 – was the difference between life and death.

He illustrates this with a few neat little guesstimates. For instance:

How much does welfare scrounging cost the economy? Guesstimate the number of scroungers. Guesstimate the value-added they'd contribute if they were working. Express as a proportion of GDP. For plausible values, it's a small number.

Or:

What impact will the small uprating in the minimum wage have on jobs? The adult rate will rise by 1.9%. Economists forecast inflation this year of 2.5%, so this is roughly a 0.6% real fall. Let's call the price-elasticity of demand for labour 1.5. The Low Pay Commission estimates (pdf) that 5.3% of jobs are around minimum wage ones. Multiply these three numbers together and we get 0.048%. Multiply by the number of jobs in the economy (29.73m) and we have roughly 14,000.That's roughly one-eleventh of the sampling variability of employment figures.

It's worth pointing out that the same idea has been applied pretty consistently to the claim that families with three generations of worklessness are a public policy problem. We don't know how many there are – and nor does the government, we now know – but study after study has suggested that the number is tiny.

There are only 15,000 households with two generations which have never worked, and a third of them are because the younger generation left full time education within the last year. On top of that, less than 1 per cent of young people have never worked by the age of 29, so the younger generation is normally the one most likely to pull a family out of worklessness. Whatever the number is, in other words, it's really, really small.

But it's important to note the downside to imprecision. The way common knowledge is disproved is rarely through wholesale upheaval. Instead, it's a gradual process of refinement: new estimates are put out, slightly lower than the old ones; then lower estimates still; and they get steadily lower, until suddenly you realise that the conventional wisdom was wrong.

It's a lot harder to turn an estimate of "recession" into an estimate of "growth" through gradual refinement than it is to turn an estimate of "-0.3 per cent" into one of "0.5 per cent". So there's more of a danger that we'll be stuck with half-truths.

But with that danger in mind, the absence of accepted imprecision is still keenly felt in Whitehall. Too frequently, "no statistics" is used to imply "we have no idea of the magnitude of this problem" – but that's not true. We actually know quite a lot, albeit imprecisely. The trick is acting on it.

Photograph: Getty Images

Alex Hern is a technology reporter for the Guardian. He was formerly staff writer at the New Statesman. You should follow Alex on Twitter.

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Manchester united: "A minority of absolute idiots are trying to break us apart"

At the vigil, one man's T-shirt read: "The only thing that's allowed to be separated by colour is the laundry."

A day after one of the worst atrocities in the history of the city, Manchester's people were keen to show the world the resilience of the Mancunian spirit.

Dom's, an Italian restaurant, is in walking distance from Manchester Arena, where 22 people lost their lives to a suicide bomber the night before. On Tuesday, the staff were giving out free coffee, tea and pizza to anyone who needed it. On a table outside, there was a condolences book, and teary passersby left RIP messages to those who perished. Under a bright blue sky, the community seemed more united than ever, the goodwill pouring out of everyone I met. But the general mood was sombre. 

"We need to make space for healing and for building up our community again, and just getting people to feel comfortable in their own city," the Dean of Manchester, Rogers Govendor, told me.

The terrorist has been named as Salman Ramadan Abedi, a 22-year-old Mancunian of Libyan descent. But with a population of 600,000, Manchester is a cosmopolitan hub, and proud of it. Throughout the day I encountered people of all skin shades and religions. On one of the roads off Albert Square, a couple of Orthodox Jewish boys set up a little stand, where people could grab a bottle of water and, if they so desired, hold hands and pray.

On the night of the tragedy, Muslim and Sikh cab drivers turned off the meter and made their way to Manchester Arena to offer free rides to anyone - many of them injured - who trying to escape the mayhem and reach safety. "It's what we do around here," my taxi driver said with a thick Arabic accent.

The dissonance between the increasingly frantic debate on social media and what was discussed on the streets was stark. I spoke, on and off the record, with about two dozen residents, eavesdropped on a number of conversations, and not once did I hear anyone speaking out against the cultural melting pot that Manchester is today. If anything, people were more eager than ever to highlight it. 

"Manchester has always been hugely multicultural, and people always pull together at times of trouble and need," said Andrew Hicklin. "They are not going to change our society and who we are as people. We live free lives."

It was also a day where political divisions were put aside. Theresa May and Jeremy Corbyn agreed to suspend their campaigns. For the next few days there will be no Labour vs Tory, no Brexiteer vs Remainer, at least not in this part of the country. This city has closed ranks and nothing will be allowed to come between that cohesion.

"I don't demonise anyone," said Dennis Bolster, who stopped by to sign the condolences book outside Dom's. "I just know a small minority of absolute idiots, driven by whatever they think they are driven by, are the people who are trying to break us apart."

Later in the day, as people were getting off work, thousands flocked to Albert Square to show their respects to the victims. Members of the Sikh community entered the square carrying "I love MCR" signs. The crowd promptly applauded. A middle-aged man wore a T-shirt which said: "The only thing that's allowed to be separated by colour is the laundry." A moment of silent was observed. It was eerie, at times overwhelmingly sad. But it was also moving and inspiring.

Local poet Tony Walsh brought brief respite from the pain when he recited "This is the Place", his ode to the city and its people. The first verse went:

This is the place In the north-west of England. It’s ace, it’s the best

And the songs that we sing from the stands, from our bands

Set the whole planet shaking.

Our inventions are legends. There’s nowt we can’t make, and so we make brilliant music

We make brilliant bands

We make goals that make souls leap from seats in the stands

On stage, everyday political foes became temporary allies. Labour leader Jeremy Corbyn, home secretary Amber Rudd, Lib Dem leader Tim Farron, Mayor of Greater Manchester Andy Burnham and house speaker John Bercow all brushed shoulders. Their message was clear: "we are Manchester too."

The vigil lasted a little over half an hour. On other occasions, a crowd this size in the centre of Manchester would give authorities reason for concern. But not this time. Everyone was in their best behaviour. Only a few were drinking. 

As Mancunians made their way home, I went over to a family that had been standing not far from me during the vigil. The two children, a boy and a girl, both not older than 10, were clutching their parents' hands the whole time. I asked dad if he will give them a few extra hugs and kisses as he tucks them in tonight. "Oh, absolutely," he said. "Some parents whose children went to the concert last night won't ever get to do that again. It's heartbreaking."

Felipe Araujo is a freelance journalist based in London. He writes about race, culture and sports. He covered the Rio Olympics and Paralympics on the ground for the New Statesman. He tweets @felipethejourno.

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