The statistics agency has published a blog post explaining why GDP estimates are regularly revised, how the process works, and what steps are being taken to sharpen the accuracy of UK economic growth data.
The gap between a first GDP estimate and the figure that eventually sticks is smaller than many people might expect. The mean absolute revision between the UK’s first quarterly GDP estimate and the same figure three years later is around 0.28 percentage points, the figures show — and the average revision between first and third estimates since around 2006 has been just minus 0.01 percentage points. Small, in other words. But those revisions still matter when they shift the story of how the economy performed.
The ONS post sets out why those changes happen at all. The first quarterly estimate is published roughly 25 to 40 days after the quarter ends, using about 80 per cent of output data — enough for a timely picture, but not a complete one. By the second estimate, coverage rises to around 93 per cent of output data, with additional expenditure and income figures added. From there, further quarterly releases and the annual Blue Book — which can take up to three years to finalise a given year’s GDP — layer in more detailed source data, updated seasonal adjustment, and methodological improvements including alignment with international standards.
Revisions around the COVID-19 period have been larger than typical. According to analysis by the National Institute of Economic and Social Research, 2020 Q2 GDP growth was revised up by around 0.5 percentage points in later Blue Book updates, and 2021 Q2 by around 1.1 percentage points. The Office for Budget Responsibility noted that cumulative real GDP growth since 2020 was revised up by around 0.5 percentage points in Blue Book 2024, with the bulk of that concentrated in 2022. ONS attributes much of this to new methods such as double deflation — using separate deflators for outputs and intermediate inputs — and updated input-output structures as more detailed sectoral data became available.
The ONS is clear that revisions are not usually corrections of errors. They are a planned part of the process, driven by late business survey responses, newly available VAT data, updated weights, and benchmarking. Unplanned corrections for identified errors are classified separately and are relatively rare.
So what does any of this mean for Kent?
GDP revisions can shift the Bank of England’s read on the economy, which in turn influences interest rate decisions affecting mortgage and loan costs for households across the county. Kent County Council, Medway Council, and NHS Kent and Medway Integrated Care Board all plan budgets against national economic forecasts; a revised picture of past growth can alter the perceived fiscal room available in future spending rounds. Businesses in logistics, tourism and manufacturing — sectors with a significant presence along the M20 corridor and the Channel crossings — may also adjust investment decisions based on reported national growth rates, making the reliability of early estimates a practical concern rather than a statistical abstraction.
The Office for Statistics Regulation oversees the handling of GDP revisions to ensure transparency and support user confidence. National Statistician Sir Ian Diamond has stated publicly that revisions are a normal part of the process and that ONS is investing in data quality and communication — including detailed blogs and technical notes — to maintain trust in the figures.
Source: @ONS