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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Why Theresa May can't end speculation of an early general election

Both Conservative and Labour MPs regard a contest next year as the solution to their problems. 

One of Theresa May’s first acts as a Conservative leadership candidate was to rule out an early general election. After a tumultuous 2015 contest and the EU referendum, her view was that the country required a period of stability (a view shared by voters). Many newly-elected Tory MPs, fearful of a Brexit-inspired Ukip or Liberal Democrat surge, supported her on this condition.

After entering Downing Street, May reaffirmed her stance. “The Prime Minister could not have been clearer,” a senior source told me. “There won’t be an early election.” Maintaining this pledge is an important part of May’s straight-talking image.

But though No.10 has wisely avoided publicly contemplating an election (unlike Gordon Brown), the question refuses to die. The Conservatives have a majority of just 12 - the smallest of any single-party government since 1974 - and, as David Cameron found, legislative defeats almost inevitably follow. May’s vow to lift the ban on new grammar schools looks to many like an unachievable task. Former education secretary Nicky Morgan and former business minister Anna Soubry are among the Tories leading the charge against the measure (which did not feature in the 2015 Conservative manifesto).  

To this problem, an early election appears to be the solution. The Tories retain a substantial opinion poll lead over Labour, the most divided opposition in recent history. An election victory would give May the mandate for new policies that she presently lacks.

“I don’t believe Theresa May wishes to hold an early election which there is evidence that the country doesn’t want and which, given the current state of the Labour Party, might be seen as opportunistic,” Nigel Lawson told today’s Times“If, however, the government were to find that it couldn’t get its legislation through the House of Commons, then a wholly new situation would arise.”

It is not only Conservatives who are keeping the possibility of an early election alive. Many Labour MPs are pleading for one in the belief that it would end Jeremy Corbyn’s leadership. An early contest would also pre-empt the boundary changes planned in 2018, which are forecast to cost the party 23 seats.

For Corbyn, the possibility of an election is a vital means of disciplining MPs. Allies also hope that the failed revolt against his leadership, which Labour members blame for the party’s unpopularity, would allow him to remain leader even if defeated.

Unlike her predecessors, May faces the obstacle of the Fixed-Term Parliaments Act (under which the next election will be on 7 May 2020). Yet it is not an insurmountable one. The legislation can be suspended with the backing of two-thirds of MPs, or through a vote of no confidence in the government. Alternatively, the act could simply be repealed or amended. Labour and the Liberal Democrats, who have demanded an early election, would struggle to resist May if she called their bluff.

To many, it simply looks like an offer too good to refuse. Which is why, however hard May swats this fly, it will keep coming back. 

George Eaton is political editor of the New Statesman.