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.

Getty Images.
Show Hide image

Voters are turning against Brexit but the Lib Dems aren't benefiting

Labour's pro-Brexit stance is not preventing it from winning the support of Remainers. Will that change?

More than a year after the UK voted for Brexit, there has been little sign of buyer's remorse. The public, including around a third of Remainers, are largely of the view that the government should "get on with it".

But as real wages are squeezed (owing to the Brexit-linked inflationary spike) there are tentative signs that the mood is changing. In the event of a second referendum, an Opinium/Observer poll found, 47 per cent would vote Remain, compared to 44 per cent for Leave. Support for a repeat vote is also increasing. Forty one per cent of the public now favour a second referendum (with 48 per cent opposed), compared to 33 per cent last December. 

The Liberal Democrats have made halting Brexit their raison d'être. But as public opinion turns, there is no sign they are benefiting. Since the election, Vince Cable's party has yet to exceed single figures in the polls, scoring a lowly 6 per cent in the Opinium survey (down from 7.4 per cent at the election). 

What accounts for this disparity? After their near-extinction in 2015, the Lib Dems remain either toxic or irrelevant to many voters. Labour, by contrast, despite its pro-Brexit stance, has hoovered up Remainers (55 per cent back Jeremy Corbyn's party). 

In some cases, this reflects voters' other priorities. Remainers are prepared to support Labour on account of the party's stances on austerity, housing and education. Corbyn, meanwhile, is a eurosceptic whose internationalism and pro-migration reputation endear him to EU supporters. Other Remainers rewarded Labour MPs who voted against Article 50, rebelling against the leadership's stance. 

But the trend also partly reflects ignorance. By saying little on the subject of Brexit, Corbyn and Labour allowed Remainers to assume the best. Though there is little evidence that voters will abandon Corbyn over his EU stance, the potential exists.

For this reason, the proposal of a new party will continue to recur. By challenging Labour over Brexit, without the toxicity of Lib Dems, it would sharpen the choice before voters. Though it would not win an election, a new party could force Corbyn to soften his stance on Brexit or to offer a second referendum (mirroring Ukip's effect on the Conservatives).

The greatest problem for the project is that it lacks support where it counts: among MPs. For reasons of tribalism and strategy, there is no emergent "Gang of Four" ready to helm a new party. In the absence of a new convulsion, the UK may turn against Brexit without the anti-Brexiteers benefiting. 

George Eaton is political editor of the New Statesman.