Osborne's dynamic plan

How a technical change in Treasury forecasting could help scrap the 45p tax rate.

At the Treasury Select Committee yesterday, in between being quizzed by MPs angry at the extent of the pre-budget leaks, George Osborne revealed that he was planning to enable the OBR to make greater use of so-called "dynamic scoring" when they prepare their economic forecasts – but only when examining tax plans. It may not sound it, but if he made that change, it would be a huge coup for the right.

Dynamic scoring is the practice of including behavioural changes in economic forecasts. Without it, in a static model, changes to revenue after something like a tax hike are facile to calculate. If VAT at 17.5 per cent takes in (say) £175bn, then VAT at 20 per cent will take in £200bn. Similarly, if you are trying to calculate the effects on government revenues of spending £100m buying new trains for the east coast main line, then you can conclude that it will cost £100m – you buy the new trains, everyone carries on riding the line, and nothing changes.

What a static model says is that people are blind to the effect that government actions have when they are choosing what to do. Clearly, that is untrue. But it is also very easy to calculate, which is why it has stuck around for so long.

Dynamic models include all these changes of behaviour. So when looking at a dynamic model for rail investment, you can take into account the fact that nicer trains will make people more likely to travel, boosting ticket revenue; and when looking at a dynamic model for VAT rises, you bear in mind the fact that as prices rise, people buy fewer things, so that an 11 per cent rise in VAT won't lead to an 11 per cent rise in VAT revenue.

The problem for economists is that dynamic models are a lot harder to calculate. Not only are there far more variables to take into account, but you open yourself up to more avenues of attack from political opponents. The combined effect of all the assumptions you must make means that your conclusions can be deeply flawed if you get too many wrong, and, as the IFS says (pdf), can "[open] the door to large controversies if these guesses are made – or perceived to be made – in a politically biased way." While static models contain assumptions that are obviously false, dynamic models still contain assumptions, which can still be just as false. And unlike static models, we can't know which ones these are until it is too late.

So why does George Osborne want to introduce dynamic scoring into OBR models? Does he believe that the government's economists have uncovered a breakthrough understanding in behavioural responses to government intervention?

A clue can be found in HMRC's report into the 50p tax rate, which found that dropping the rate down to 45p would cost far less than expected, because of expected behavioural changes. Indeed, this sort of dynamic thinking is the cornerstone of the Laffer curve, the economic theory that, past a certain point, increasing tax rates reduces revenues.

What Osborne will be hoping is that allowing the OBR to make its models more dynamic still will strengthen the rationale for scrapping the 45p rate entirely, as well as for cutting corporation tax all the way down to 20p by the end of parliament.

Yet while the OBR will be "informed" by these new dynamic models when it comes to tax policy, they won't be taking account of the same information when examining the justification for government investment, where, far from strengthening Osborne's preferred policy, it would weaken it. If dynamic scoring is indeed implemented in this narrow fashion, Osborne will have scored a stealth victory for future Tory policy.

Money on the mind: A 19th century phrenology chart. Credit: Getty

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

David Cameron addresses pupils at an assembly during a visit to Corby Technical School on September 2, 2015. Photograph: Getty Images.
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Can Cameron maintain his refugee stance as he comes under attack from all sides?

Tory MPs, the Sun, Labour and a growing section of the public are calling on the PM to end his refusal to take "more and more". 

The disparity between the traumatic images of drowned Syrian children and David Cameron's compassionless response ("I don't think there is an answer that can be achieved simply by taking more and more refugees") has triggered a political backlash. A petition calling for greater action (the UK has to date accepted just 216 refugees) has passed the 100,000 threshold required for the government to consider a debate after tens of thousands signed this morning. Scottish Conservative leader Ruth Davidson has tweeted: "This is not an immigration issue, it's a humanitarian one, and the human response must be to help. If we don't, what does that make us?" Tory MPs such as Nicola Blackwood, David Burrowes, Jeremy Lefroy and Johnny Mercer have similarly appealed to Cameron to reverse his stance.

Today's Sun declares that the UK has "a proud record of taking in desperate people and we should not flinch from it now if it is beyond doubt that they have fled for their lives." Meanwhile, the Washington Post has published a derisive piece headlined "Britain takes in so few refugees from Syria they would fit on a subway train". Labour has called on Cameron to convene a meeting of Cobra to discuss the crisis and to request an emergency EU summit. Yvette Cooper, who led the way with a speech on Monday outlining how the UK could accept 10,000 refugees, is organising a meeting of councils, charities and faith groups to discuss Britain's response. Public opinion, which can turn remarkably quickly in response to harrowing images, is likely to have grown more sympathetic to the Syrians' plight. Indeed, a survey in March found that those who supported accepting refugees fleeing persecution outnumbered opponents by 47-24 per cent. 

The political question is whether this cumulative pressure will force Cameron to change his stance. He may not agree to match Cooper's demand of 10,000 (though Germany is poised to accept 800,000) but an increasing number at Westminster believe that he cannot remain impassive. Surely Cameron, who will not stand for election again, will not want this stain on his premiership? The UK's obstinacy is further antagonising Angela Merkel on whom his hopes of a successful EU renegotiation rest. If nothing else, Cameron should remember one of the laws of politics: the earlier a climbdown, the less painful it is. 

George Eaton is political editor of the New Statesman.