Vanishing Populations: Millions Are Missing From Global Census Counts

Foreign aid cuts will make the ongoing ‘quiet crisis’ even worse, according to experts.

Researchers warn that millions of people worldwide are missing from census and survey data, leaving policymakers without crucial information about the populations they are responsible for.

They describe a ‘quiet crisis’ emerging as response rates fall and concerns grow over the reliability of the data.

Pandemic and policy erosion deepen the issue

In a paper published in Science, researchers from the University of Southampton and Columbia University highlight a ‘perfect storm’ of disruptions caused by the COVID-19 pandemic, declining public trust in institutions, and a breakdown in international support.

They explain that recent cuts to foreign aid by the USA, the UK, and several other European countries are likely to make the problem even worse.

“Lack of census data compromises all areas of public administration, but we don’t see these statistics in the same way as other vital infrastructure, like bridges or roads,” says Dr Jessica Espey, lead author of the paper from the University of Southampton and Deputy Director of its WorldPop research team, which provides data on population distribution, demographics and dynamics.

“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 stakes of being uncounted

Decisions about where to build hospitals or how to distribute resources for schools depend on knowing how many people live in each area and who they are. This kind of information becomes especially critical during emergencies, such as disease outbreaks or natural disasters.

Censuses, which have been used by governments since Roman times, provide these essential data. They help authorities allocate resources effectively and plan for future challenges, whether it involves an ageing population or a growing younger one.

But the percentage of the world’s population covered by up-to-date censuses, conducted every ten years, has declined. Additionally, 24 of the 204 countries that carried out a census between 2015 and 2024, representing a quarter of the world’s population, haven’t published their results.

Census post-enumeration surveys, which independently assess the completeness of a census, suggest a decline in accuracy and coverage. The 2020 US Census likely undercounted the US Latino population by 2.9 million people, while the 2022 South African census undercounted its overall population by up to 31%. The UN estimates that one in three Africans were not counted in the 2020 census round.

Accuracy gaps in post-census checks

The COVID-19 pandemic disrupted traditional house-to-house interviews and impacted funding. Researchers also highlight growing distrust in national governments, with some communities fearing immigration-related law enforcement or AI-supported decision-making will use their data against them, and others worried about the threat of data leaks and cyberattacks.

In February of this year, the Trump administration cut support for the Demographic and Health Surveys (DHS) program, which provided vital data on populations across 90 countries for four decades, often filling gaps left by lack of census data. Other countries like the UK, France, and the Netherlands have reallocated development assistance to defense spending, reducing both direct assistance to countries and also to UN agencies that provide support on censuses and surveys.

A paradox of data abundance

“We live in an era of seemingly unlimited data, yet some of our most essential demographic information is deteriorating, introducing known and unknown bias into decision making,” says co-author Dr Dana Thomson from Columbia University.

The researchers say new technologies, such as AI-derived building footprints from satellite images, can support the planning and implementation of censuses and potentially reduce costs, pointing to recent successes in multiple countries that WorldPop has supported, such as the Democratic Republic of the Congo.

They also say governments need to do more to build trust, demonstrate how census data affects people’s daily lives and be transparent about how this data is used to inform decisions.

Professor Andrew Tatem, a coauthor of the paper who leads WorldPop at Southampton, says: “In an era of growing challenges, from climate change to economic inequality, accurate population data is not a luxury – it is essential infrastructure for healthy, resilient, functioning societies.

“The current undercounting of populations creates a negative feedback loop, leaving governments with less accurate information on the communities most in need. This threatens both statistical accuracy and the very foundations of equitable governance.

“By combining technological innovation with renewed public trust and international cooperation, we can ensure that everyone is counted – and everyone counts.”

Reference: “Disappearing people: A global demographic data crisis threatens public policy” by Jessica M. Espey, Andrew J. Tatem and Dana R. Thomson, 19 June 2025, Science.
DOI: 10.1126/science.adx8683

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