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.

Getty
Show Hide image

What type of Brexit did we vote for? 150,000 Conservative members will decide

As Michael Gove launches his leadership bid, what Leave looks like will be decided by Conservative activists.

Why did 17 million people vote to the leave the European Union, and what did they want? That’s the question that will shape the direction of British politics and economics for the next half-century, perhaps longer.

Vote Leave triumphed in part because they fought a campaign that combined ruthless precision about what the European Union would do – the illusory £350m a week that could be clawed back with a Brexit vote, the imagined 75 million Turks who would rock up to Britain in the days after a Remain vote – with calculated ambiguity about what exit would look like.

Now that ambiguity will be clarified – by just 150,000 people.

 That’s part of why the initial Brexit losses on the stock market have been clawed back – there is still some expectation that we may end up with a more diluted version of a Leave vote than the version offered by Vote Leave. Within the Treasury, the expectation is that the initial “Brexit shock” has been pushed back until the last quarter of the year, when the election of a new Conservative leader will give markets an idea of what to expect.  

Michael Gove, who kicked off his surprise bid today, is running as the “full-fat” version offered by Vote Leave: exit from not just the European Union but from the single market, a cash bounty for Britain’s public services, more investment in science and education. Make Britain great again!

Although my reading of the Conservative parliamentary party is that Gove’s chances of getting to the top two are receding, with Andrea Leadsom the likely beneficiary. She, too, will offer something close to the unadulterated version of exit that Gove is running on. That is the version that is making officials in Whitehall and the Bank of England most nervous, as they expect it means exit on World Trade Organisation terms, followed by lengthy and severe recession.

Elsewhere, both Stephen Crabb and Theresa May, who supported a Remain vote, have kicked off their campaigns with a promise that “Brexit means Brexit” in the words of May, while Crabb has conceded that, in his view, the Leave vote means that Britain will have to take more control of its borders as part of any exit deal. May has made retaining Britain’s single market access a priority, Crabb has not.

On the Labour side, John McDonnell has set out his red lines in a Brexit negotiation, and again remaining in the single market is a red line, alongside access to the European Investment Bank, and the maintenance of “social Europe”. But he, too, has stated that Brexit means the “end of free movement”.

My reading – and indeed the reading within McDonnell’s circle – is that it is the loyalists who are likely to emerge victorious in Labour’s power struggle, although it could yet be under a different leader. (Serious figures in that camp are thinking about whether Clive Lewis might be the solution to the party’s woes.) Even if they don’t, the rebels’ alternate is likely either to be drawn from the party’s Brownite tendency or to have that faction acting as its guarantors, making an end to free movement a near-certainty on the Labour side.

Why does that matter? Well, the emerging consensus on Whitehall is that, provided you were willing to sacrifice the bulk of Britain’s financial services to Frankfurt and Paris, there is a deal to be struck in which Britain remains subject to only three of the four freedoms – free movement of goods, services, capital and people – but retains access to the single market. 

That means that what Brexit actually looks like remains a matter of conjecture, a subject of considerable consternation for British officials. For staff at the Bank of England,  who have to make a judgement call in their August inflation report as to what the impact of an out vote will be. The Office of Budget Responsibility expects that it will be heavily led by the Bank. Britain's short-term economic future will be driven not by elected politicians but by polls of the Conservative membership. A tense few months await. 

Stephen Bush is special correspondent at the New Statesman. He usually writes about politics.