“Exposed: Shocking Truth about the Reliability of UK Migration Statistics!”

Statisticians question the accuracy of official data underpinning UK government policies after the latest migration figures fell significantly outside analysts’ expectations.

Last week, experts were puzzled when the Office for National Statistics reported that net migration had peaked 606,000 in 2022. While that figure marked a record for the UK, it also represented a relative flatness from the previous two quarters, far from the jump analysts had expected.

While upward revisions to previous estimates have contributed to the gap between expectations and official data, experts point to another factor: the ONS’s decision to reform the way it calculates migration data.

“THE ONS is starting to transform the way these [migration] the statistics are estimated and it’s very transparent about it, but it’s quite complicated and technical,” said Alan Manning, a professor at the London School of Economics and former chair of the Migration Advisory Committee, which advises the government.

“Did the stock figure just go up because they’re changing methodology or because of something underlying?”

The disparity between the official figures and analysts’ projections has sparked debate among experts, with some questioning the suitability of the UK’s new methodology, which underpins government policy, for the purpose.

Net migration is calculated by estimating how many people migrate to the UK for at least one year and subtracting the number of long-term residents emigrating abroad.

The ONS had previously based its migration estimates on a questionnaire conducted at airports such as Heathrow and Manchester called the International Passenger Survey. However, it has bypassed major gateways to other parts of the country, such as Luton and Leeds.

The department has long admitted the the approach was flawed. In 2019, the data was stripped of the “national statistic” stamp of approval after the survey revealed it systematically underestimated the EU and overestimated the EU’s net migration.

Since April 2021, the ONS has produced an “experimental” migration dataset using administrative data, such as visas and tax records, along with statistical modeling and other surveys.

Madeleine Sumption, director of the University of Oxford’s Observatory on Migration, pointed to the potential limitations of the new approach.

“Administrative data sources have many advantages, but they are also less transparent,” he said. “There are a lot of tricky technical issues that affect the estimates in ways that aren’t always easy to predict.”

Uncertainty about the accuracy of migration data presents a challenge for policy makers and statisticians, who rely on them to produce population estimates between censuses.

Simon Briscoe, a former statistical adviser to the House of Commons Public Administration Select Committee dealing with migration, said the “rough and ready” figures used in the new data collection system were “almost meaningless”. .

“To have sensible policies to fill gaps in labor markets and make sure there are enough staff in the NHS we need accurate data and we don’t have it.”

The Home Office declined to comment.

The ONS relies on a data mosaic to estimate the main migration statistic. Calculating non-EU numbers is easier because people in this group require visas, while many EU citizens have stable status and can therefore travel without one.

However, the ONS has yet to adjust to the fact that not everyone who has been granted a visa should be counted in the statistics. Some visa holders stay less than a year, while others don’t come at all.

Measuring emigration from the UK is also challenging because people can leave before their visa expires.

Recent methodology changes show how count changes can substantially affect the stock number.

For example, Ukrainian refugees were previously considered long-term migrants. But 39,000 people were removed from the latest estimates based on data suggesting some stayed in the UK for less than a year.

Measuring asylum seekers is also challenging as this group is not typically reflected in Home Office border systems data. For the first time this year they have been included in migration statistics, with figures based on the number of complaints registered.

The ONS acknowledged that its methods were “clearly experimental and in development” but insisted on confidence that the statistics were “the best possible estimates from the available data”.

He added that they were supported by many sources, including the 2021 census, using methods developed in consultation with industry experts.

“These new methods are based on actual travel patterns, rather than respondents’ stated intentions. While this provides a more accurate picture of migration in general, it takes time to get a full picture of people’s behavior.”