A review by the Office for Statistics Regulation (OSR) has examined a persistent pattern in recent GDP data, with stronger growth in the first half of the year than in the second. While there is currently no statistical evidence that this pattern reflects a problem with seasonal adjustment, OSR considers it important that producers and users remain alert to it and continue to monitor developments closely.
The work was prompted by concerns from some users and media commentators about the effectiveness of seasonal adjustment in the post‑pandemic period. Recent quarterly and monthly GDP statistics published by ONS show stronger growth in the first part of the year, reflecting at least in part a series of one‑off events – for example, activity being brought forward in anticipation of increased tariffs.
Current statistical tests show no evidence of significant residual seasonality in quarterly or monthly GDP, and ONS’s approach is consistent with internationally recognised practice. However, because emerging seasonal patterns can take several years to detect using standard methods, it is important to keep an open mind. Early signs of change may not yet be visible in the statistical tests, so continued vigilance and transparency remain essential.
To strengthen ONS’s approach going forward, OSR has recommended that ONS should:
- Seek external assurance on its approach, particularly on the detection of emerging seasonal signals.
- Continue increasing transparency around its methods and uncertainties.
- Complete work to rebuild and stabilise the specialist team responsible for seasonal adjustment.
Ed Humpherson, DG Regulation, said:
“It remains essential for both ONS and users of GDP statistics to keep an open mind as newly emerging patterns in the data evolve.
“ONS’s proactive engagement with our recommendations, and its commitment to enhancing the scrutiny of seasonal adjustment processes, will help ensure the continued trustworthiness of these key statistics.”
Compliance review of Treatment of Seasonality in Quarterly GDP statistics – March 2026
Notes to editors
- Here is OSR’s final economics statistics report published in November 2025. This followed the initial review published in April 2025.
- Here is ONS’s strategic improvement update. OSR responded to this in December 2025.
- The Office for Statistics Regulation (OSR) provides independent regulation of all official statistics produced in the UK, and aims to enhance public confidence in the trustworthiness, quality and value of statistics produced by government. OSR regulates statistics by setting the standards official statistics must meet in the Code of Practice for Statistics. We ensure that producers of official statistics uphold these standards by conducting assessments against the Code. Those which meet the standards are given accredited official statistics status, indicating that they meet the highest standards of trustworthiness, quality and value. We also report publicly on systemwide issues and on the way that statistics are being used, celebrating when the standards are upheld and challenging publicly when they are not. OSR is independent from government ministers, and separate from producers of statistics, including the Office for National Statistics (ONS).
- OSR’s Director General, Ed Humpherson, reports directly to the Chair of the UK Statistics Authority Board. The Director General, and OSR, have wide discretion in highlighting good practice and reporting concerns with the production and use of statistics publicly. OSR’s work is overseen by the Board’s regulation committee (made up of non-executive directors, and with no statistical producer in attendance). OSR’s budget is proposed by the Board’s regulation committee and endorsed by the Board.
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