ONS decides to continue with inaccurate RPI calculation

Statistics agency chooses consistency over accuracy.

Against expectations and the recommendations of a number of influential economists, as well as its own consumer prices advisory committee, the ONS has decided not to change how the RPI – one of the two key indices measuring the rate of price inflation – is calculated.

The pressure to examine the index comes from the longstanding difference between the RPI and CPI measures of inflation. Except for the brief period in the midst of the recession, when both indices were recording deflation, RPI has consistently shown levels of inflation higher than CPI. Here's the chart for the last three years, for instance:


Some of that difference is due to the fact that the two indices measure subtly different things – RPI includes a broader measure of housing costs, for instance, and it ignores very high and low income households. But the ONS has known for a while that there is also a discrepancy caused by the different formulae used to calculate them.

The ONS began a consultation into whether and how it should eliminate this "formula effect", and has concluded that:

Use of the arithmetic formulation (known as the ‘Carli’ index formula) in the RPI is the primary source of the formula effect difference between the RPI and the CPI… This formulation does not meet current international standards.

So what's it going to do about it? Well, nothing:

The National Statistician also noted that there is significant value to users in maintaining the continuity of the existing RPI’s long time series without major change, so that it may continue to be used for long-term indexation and for index-linked gilts and bonds in accordance with user expectations.

Therefore, while the arithmetic formulation would not be chosen were ONS constructing a new price index, the National Statistician recommended that the formulae used at the elementary aggregate level in the RPI should remain unchanged.

The ONS will, however, develop a new measure of inflation, called RPIJ, which will use a different, better, mathematical formula.

The consumer prices advisory committee, a body which meets around five times a year to advise the ONS on measures of inflation, accepted that the ONS has a responsibility to make sure that there is a level of continuity in the RPI calculations which would be destroyed if there were a change to the formula. But, given the ONS also has a responsibility to compile those statistics "in line with best practice", CPAC concluded that not changing RPI would be "unsuitable".

On the other side, arguing for no change, were 332 of the 406 replies to the public consultation. The ONS said:

The large majority of responses did not address methodological issues but identified the impact that the changes implied… would have for them.

The competing requirements present a tricky path for the ONS to follow, but it does feel like it has picked the wrong option at this point. The job of the statistics agency is surely to produce accurate statistics, rather than statistics which are continually inaccurate in known ways. The fact that RPI is used to decide the value of, amongst other things, index-linked bonds is a reason for it to be correct, not for it to be artificially inflated.

As it stands, the ONS has decided to continue publishing a "measure" of inflation which has an accepted and understood upward bias of 1 per cent a year. It has done this, not because of any real statistical reasoning, but because greater accuracy would be bad for a majority of stakeholders. That seems like a bizarre abdication of its duty.

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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Could Labour lose the Oldham by-election?

Sources warn defeat is not unthinkable but the party's ground campaign believe they will hold on. 

As shadow cabinet members argue in public over Labour's position on Syria and John McDonnell defends his Mao moment, it has been easy to forget that the party next week faces its first election test since Jeremy Corbyn became leader. On paper, Oldham West and Royton should be a straightforward win. Michael Meacher, whose death last month triggered the by-election, held the seat with a majority of 14,738 just seven months ago. The party opted for an early pre-Christmas poll, giving second-placed Ukip less time to gain momentum, and selected the respected Oldham council leader Jim McMahon as its candidate. 

But in recent weeks Labour sources have become ever more anxious. Shadow cabinet members returning from campaigning report that Corbyn has gone down "very badly" with voters, with his original comments on shoot-to-kill particularly toxic. Most MPs expect the party's majority to lie within the 1,000-2,000 range. But one insider told me that the party's majority would likely fall into the hundreds ("I'd be thrilled with 2,000") and warned that defeat was far from unthinkable. The fear is that low turnout and defections to Ukip could allow the Farageists to sneak a win. MPs are further troubled by the likelihood that the contest will take place on the same day as the Syria vote (Thursday), which will badly divide Labour. 

The party's ground campaign, however, "aren't in panic mode", I'm told, with data showing them on course to hold the seat with a sharply reduced majority. As Tim noted in his recent report from the seat, unlike Heywood and Middleton, where Ukip finished just 617 votes behind Labour in a 2014 by-election, Oldham has a significant Asian population (accounting for 26.5 per cent of the total), which is largely hostile to Ukip and likely to remain loyal to Labour. 

Expectations are now so low that a win alone will be celebrated. But expect Corbyn's opponents to point out that working class Ukip voters were among the groups the Labour leader was supposed to attract. They are likely to credit McMahon with the victory and argue that the party held the seat in spite of Corbyn, rather than because of him. Ukip have sought to turn the contest into a referendum on the Labour leader's patriotism but McMahon replied: "My grandfather served in the army, my father and my partner’s fathers were in the Territorial Army. I raised money to restore my local cenotaph. On 18 December I will be going with pride to London to collect my OBE from the Queen and bring it back to Oldham as a local boy done good. If they want to pick a fight on patriotism, bring it on."  "If we had any other candidate we'd have been in enormous trouble," one shadow minister concluded. 

Of Corbyn, who cancelled a visit to the seat today, one source said: "I don't think Jeremy himself spends any time thinking about it, he doesn't think that electoral outcomes at this stage touch him somehow."  

George Eaton is political editor of the New Statesman.