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.

Photo: Getty
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After Richmond Park, Labour MPs are haunted by a familiar ghost

Labour MPs in big cities fear the Liberal Democrats, while in the north, they fear Ukip. 

The Liberal Democrats’ victory in Richmond Park has Conservatives nervous, and rightly so. Not only did Sarah Olney take the votes of soft Conservatives who backed a Remain vote on 23 June, she also benefited from tactical voting from Labour voters.

Although Richmond Park is the fifth most pro-Remain constituency won by a Conservative at the 2015 election, the more significant number – for the Liberal Democrats at least – is 15: that’s the number of Tory-held seats they could win if they reduced the Labour vote by the same amount they managed in Richmond Park.

The Tories have two Brexit headaches, electorally speaking. The first is the direct loss of voters who backed David Cameron in 2015 and a Remain vote in 2016 to the Liberal Democrats. The second is that Brexit appears to have made Liberal Democrat candidates palatable to Labour voters who backed the party as the anti-Conservative option in seats where Labour is generally weak from 1992 to 2010, but stayed at home or voted Labour in 2015.

Although local council by-elections are not as dramatic as parliamentary ones, they offer clues as to how national elections may play out, and it’s worth noting that Richmond Park wasn’t the only place where the Liberal Democrats saw a dramatic surge in the party’s fortunes. They also made a dramatic gain in Chichester, which voted to leave.

(That’s the other factor to remember in the “Leave/Remain” divide. In Liberal-Conservative battlegrounds where the majority of voters opted to leave, the third-placed Labour and Green vote tends to be heavily pro-Remain.)

But it’s not just Conservatives with the Liberal Democrats in second who have cause to be nervous.  Labour MPs outside of England's big cities have long been nervous that Ukip will do to them what the SNP did to their Scottish colleagues in 2015. That Ukip is now in second place in many seats that Labour once considered safe only adds to the sense of unease.

In a lot of seats, the closeness of Ukip is overstated. As one MP, who has the Conservatives in second place observed, “All that’s happened is you used to have five or six no-hopers, and all of that vote has gone to Ukip, so colleagues are nervous”. That’s true, to an extent. But it’s worth noting that the same thing could be said for the Liberal Democrats in Conservative seats in 1992. All they had done was to coagulate most of the “anyone but the Conservative” vote under their banner. In 1997, they took Conservative votes – and with it, picked up 28 formerly Tory seats.

Also nervous are the party’s London MPs, albeit for different reasons. They fear that Remain voters will desert them for the Liberal Democrats. (It’s worth noting that Catherine West, who sits for the most pro-Remain seat in the country, has already told constituents that she will vote against Article 50, as has David Lammy, another North London MP.)

A particular cause for alarm is that most of the party’s high command – Jeremy Corbyn, Emily Thornberry, Diane Abbott, and Keir Starmer – all sit for seats that were heavily pro-Remain. Thornberry, in particular, has the particularly dangerous combination of a seat that voted Remain in June but has flirted with the Liberal Democrats in the past, with the shadow foreign secretary finishing just 484 votes ahead of Bridget Fox, the Liberal Democrat candidate, in 2005.

Are they right to be worried? That the referendum allowed the Liberal Democrats to reconfigure the politics of Richmond Park adds credence to a YouGov poll that showed a pro-Brexit Labour party finishing third behind a pro-second referendum Liberal Democrat party, should Labour go into the next election backing Brexit and the Liberal Democrats opt to oppose it.

The difficulty for Labour is the calculation for the Liberal Democrats is easy. They are an unabashedly pro-European party, from their activists to their MPs, and the 22 per cent of voters who back a referendum re-run are a significantly larger group than the eight per cent of the vote that Nick Clegg’s Liberal Democrats got in 2015.

The calculus is more fraught for Labour. In terms of the straight Conservative battle, their best hope is to put the referendum question to bed and focus on issues which don’t divide their coalition in two, as immigration does. But for separate reasons, neither Ukip nor the Liberal Democrats will be keen to let them.

At every point, the referendum question poses difficulties for Labour. Even when neither Ukip nor the Liberal Democrats take seats from them directly, they can hurt them badly, allowing the Conservatives to come through the middle.

The big problem is that the stance that makes sense in terms of maintaining party unity is to try to run on a ticket of moving past the referendum and focussing on the party’s core issues of social justice, better public services and redistribution.

But the trouble with that approach is that it’s alarmingly similar to the one favoured by Kezia Dugdale and Scottish Labour in 2016, who tried to make the election about public services, not the constitution. They came third, behind a Conservative party that ran on an explicitly pro-Union platform. The possibility of an English sequel should not be ruled out.  

Stephen Bush is special correspondent at the New Statesman. His daily briefing, Morning Call, provides a quick and essential guide to British politics.