The UK’s gender pay gap has been underestimated for more than 20 years, according to research that could raise fresh questions about the quality of data used to inform key pay decisions across the UK.
The findings, released in the British Journal of Industrial Relations on Monday, suggest that, since 2004, the Office for National Statistics (ONS) had failed to properly account for the fact that it received more data from larger employers, when it reported its annual survey of hours and earnings (Ashe).
It meant the survey gave undue weighting to large businesses, where pay was higher and the difference in pay between men and women was generally smaller. As a result, it gave too little to smaller private businesses, particularly surrounding pay and representation for women.
That resulted in the ONS consistently underestimating the gender pay gap by a “small but noteworthy” margin of one percentage point, the research paper said.
The research paper’s lead author, Prof John Forth from the Bayes Business School at City St George’s, University of London, said the data collected in this annual survey “has far-reaching consequences across our society, informing everything from official pay recommendations for doctors and nurses to anti-poverty measures like the national minimum wage. It is, therefore, crucial that the data is a true representation of wages and earnings in modern Britain.”
The flawed data may have influenced key pay decisions. The Ashe survey is used by the Low Pay Commission to monitor the impact of the minimum wage, and by the Office for the Pay Review Bodies to help determine public sector pay settlements. It is the latest blow to the ONS, which has struggled with mounting problems that have forced it to delay or cancel several of its releases in recent months
The ONS did not immediately respond to the Guardian’s request for comment but told the Financial Times that the survey’s sampling and weighting was under review and that the agency had improved its approach to the survey since 2024 in a way that would address some of the issues raised in the report.
“Weighting schemes are just one aspect of the methodology of a complex survey such as Ashe, and we regularly scrutinise these methods to ensure they continue to be relevant and aligned to best practice,” the ONS added.
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Forth said he welcomed the ONS review. “We encourage them to look at how the data can be made more representative of jobs in all types of organisations, so that the issues we observed can be addressed.”