Millions of people are missing from official population data.

Researchers from the University of Southampton and Columbia University warn that this data gap is undermining government planning and resource allocation, leading to "political underrepresentation" and "inadequate resource allocation."

The study blames falling census response rates on a "perfect storm" of factors, including the Covid-19 pandemic, reduced international aid, and growing public distrust in government.

Dr Jessica Espey, lead author and deputy director of the University of Southampton’s WorldPop research team, said: "When groups are not counted, they can be left off the policy agenda.

"That political underrepresentation and the inadequate resource allocation that follows can have pernicious effects."

The paper, published in Science, highlights that the 2020 US census missed nearly three million Latino residents, while South Africa’s 2022 census undercounted its population by up to 31 per cent.

It also notes that 24 countries have not published census results from surveys conducted between 2015 and 2024.