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UK migration statistics lose their ‘National Statistics’ status as ONS confirms problems measuring EU and non-EU net migration

21 Aug 2019

New analysis from the Office for National Statistics shows that official data have been systematically underestimating net migration from EU countries, while overestimating non-EU net migration. ONS’ decision to remove the ‘National Statistics’ quality badge from their immigration and net migration statistics is a sensible move to help users understand that the figures are still not fully reliable, the Migration Observatory at the University of Oxford said today.

Over the past two years, ONS has been working to identify why the International Passenger Survey, a high-profile dataset that was widely used to assess the government’s attempts to meet its ‘tens of thousands’ net migration target, was inconsistent with other data sources.

In an important new report, ONS has concluded that official estimates of EU net migration to the UK from the mid-2000s until 2016 were too low. The precise size of the undercount is not yet known. However, an initial set of adjusted figures published in an ONS technical report have increased the official estimate of EU net migration by 16% or 29,000 for the year ending March 2016, which was the most recent period for which the adjustment was possible. This means an increase in the estimate of EU migration from 178,000 to 207,000 for the year ending March 2016.

The adjustments do not increase the estimate of the EU citizen population in the UK, which comes from a different data source and remains at 3,640,000 for 2018. ONS has not yet produced adjusted EU net migration figures for 2017 and 2018, and we cannot assume that EU migration post-referendum has necessarily been underestimated. This is because of sharp changes in migration patterns in the most recent period.

At the same time, ONS has concluded that estimates of non-EU net migration have been too high, primarily because the IPS underestimates the emigration of non-EU international students. Adjusted figures published today for non-EU net migration are 13% (or 25,000) lower than previous estimates in the year ending March 2016, and 8% or 18,000 lower for 2018.

These two corrections broadly cancel each other out. As a result, ONS’ assessment of overall net migration up to the year ending March 2016 is largely unchanged, increasing by 4,000 or 1% in that period.

Importantly, the adjustments published today do not yet close the unexplained gap between different data sources. The new figures are deemed experimental and it is possible that further ONS work will lead to more adjustments in the same direction.

Madeleine Sumption, Director of the Migration Observatory at the University of Oxford, said: “We have been pointing out for a while that something wasn’t quite right in the net migration statistics, and that the comparison of EU vs. non-EU net migration did not seem plausible. This matters because for the past 9 years the UK policy debate has been fixated on a single data source, which couldn’t bear the load that it was forced to carry. Whether the question is how to meet the net migration target or what to do about international students, the truth is that the data were simply not robust enough to be picked apart in such detail. The quarterly drumbeat of migration statistics that has become a feature of the UK migration debate arguably just overdramatised small changes in figures that were always quite uncertain.”

ONS has also said on a number of occasions that the net migration figures had been ‘stretched beyond their purpose’.

Sumption added: “Today’s report from ONS is an important step towards more useful figures. The story isn’t over, though – there is more work to do and it wouldn’t be surprising to see more revisions in the same direction in the future. The decision to label the statistics as ‘experimental’ makes sense, as it should help to convey to politicians and policymakers that the figures can’t be treated as the absolute truth and are still subject to a lot of uncertainty.”

The adjusted EU migration figures outlined in today’s report do not cover the most recent period after early 2016, because the DWP data used to produce the adjustment were not yet available for ONS to use. ONS notes that EU migration trends changed sharply after the referendum, and that its ‘best assessment’ is that overall net migration after 2016 may be ‘slightly lower’ than the published estimates.


Notes for editors:

  • Official statistics can be labelled as ‘experimental statistics’ when they are going through development and do not yet meet the quality standards required of ‘National Statistics’. National Statistics are expected to meet a set of requirements including a high degree of accuracy and reliability.
  • The technical report published today outlines a new methodology for producing the net migration statistics, which are due to be published tomorrow in full.

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