Question to the Cabinet Office:

To ask His Majesty's Government how many times since the 2021 Census the Office for National Statistics (ONS) has (1) varied a published official statistic, (2) reverted a statistic to “development stage", and (3) downgraded a forecast; and how often the ONS has published data since April 2021 on (a) quarterly economic growth, and (b) migration statistics.

The information requested falls under the remit of the UK Statistics Authority.

Please see the letter attached from the National Statistician and Chief Executive of the UK Statistics Authority.

The Rt Hon. the Lord Blunkett

House of Lords

London

SW1A 0PW

14 October 2024

Dear Lord Blunkett,

As National Statistician and Chief Executive of the UK Statistics Authority, I am responding to your Parliamentary Question asking how many times since the 2021 Census the Office for National Statistics (ONS) has (1) varied a published official statistic, (2) reverted a statistic to “development stage", and (3) downgraded a forecast; and how often the ONS has published data since April 2021 on (a) quarterly economic growth, and (b) migration statistics (HL1172).

Changes or updates to published official statistics are sometimes required for various reasons. We use different terminology depending on the reason for the change or update. These terms are “correction of errors” and “revisions”.

Despite having quality control measures in place, mistakes may be found in our statistics. Correction of errors are amendments that are made to published statistics in response to the identification of mistakes following their initial publication. Since the 2021 Census (21 March 2021), we have published 3,763 statistical releases1 and made 577 corrections; however, the vast majority (553, or 96%) of these corrections were for minor errors which did not materially affect the interpretation or use of the statistics. The table below shows the breakdown by calendar year:

Revisions are updates to previously published statistics that improve quality by incorporating improved methods, additional data sources or statistics that were unavailable at the point of initial publication. Revisions should not be confused with the correction of errors; revisions are not published to correct a mistake. We do not hold the number of revisions made to official statistics in one centralised source, as these are a standard part of our process. Our Revisions and Corrections policies2 expand on the difference in more detail.

Accredited official statistics are a sub-set of official statistics that have been independently reviewed by the Office for Statistics Regulation and confirmed as complying with the standards of trustworthiness, quality and value in the Code of Practice for Statistics.

Official statistics in development are official statistics that are undergoing a development; they may be new or existing statistics, and will be tested with users, in line with the standards of trustworthiness, quality, and value in the Code of Practice for Statistics. The designation does not mean that the statistics are of poor quality and even though the statistics are going through development and testing, we are confident that they are useful.

Since 21 March 2021 there have been three instances where accredited official statistics have changed to “official statistics in development”. These are Employment in the UK (14 November 2023, Correspondence3), Gender identity, England and Wales: Census 2021 (12 September 2024, Correspondence4), and Annual Population Survey estimates (9 October 2024, Correspondence5).

We do not hold data on non-accredited official statistics that have become "official statistics in development".

There are also a small number of ONS outputs that have reverted from “accredited official statistics” to “official statistics” status, but these are not “official statistics in development”. In most cases the change in designation is at the request of the producer to signal to users that the statistics no longer comply fully with the standards in the Code of Practice for Statistics. The Office for Statistics Regulation maintains a list6 of all accredited official statistics that have been de-designated.

The ONS does not make forecasts, estimates or predictions about future events or trends.

Since April 2021, the ONS has released the latest data on quarterly economic growth on a quarterly basis in 28 publications of the GDP first quarterly estimate and GDP quarterly national accounts. Over the same period the ONS has published long-term international migration statistics on a bi-annual basis, six times in total. These releases contain revisions to improve the quality and reduce the uncertainty of previously published estimates by using more up to date data, in line with international best practice standards.

The ONS has published a range of further analysis and commentary on both topics, but those publications are based on previously published data first made available via the releases outlined above.

Yours sincerely,

Professor Sir Ian Diamond

1Including statistical bulletins, analytical articles, methodology papers and data tables.

2https://www.ons.gov.uk/methodology/methodologytopicsandstatisticalconcepts/revisions/guidetostatisTicalrevisions

3Exchange of letters between Ed Humpherson (OSR) and Alex Lambert and Darren Morgan (ONS) -

Office for National Statistics

4ONS letter to the OSR on Census 2021 gender identity estimates - Office for National Statistics

5Michael Keoghan to Siobhan Tuohy-Smith: Request to suspend APS accreditation – Office for

Statistics Regulation (statisticsauthority.gov.uk)

6https://osr.statisticsauthority.gov.uk/our-regulatory-work/assessment/cancelled-or-suspended-accreditations/