Millions of people around the world are not being included in census and survey data, according to a study published in Science. This makes it harder for policymakers to understand the population they govern.
A team of researchers from the University of Southampton, UK, say that a crisis is unfolding, as more people decline to complete the surveys putting in danger the accuracy of the data collected. The authors suggest that the disruptions caused by the COVID-19 aggravated the problem, decreasing confidence in institutions and collapsing international support. They add that cuts to aid budgets from the USA, the UK and other European countries will worsen the situation.
“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,” said 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.”
This may affect decisions about where to build an hospital or allocate resources for schools. Access to accurate information is especially important during a crisis or a natural disaster. Censuses also provide the data that helps governments decide how to direct resources and anticipate future challenges and opportunities, such as an ageing population or a burgeoning younger one.
The problem is the the % of the world’s population covered by up-to-date censuses has declined. Additionally, some of the countries that carried out a census between 2015 and 2024 haven’t published their results.
Post-census surveys to assess the completeness of a census suggest a decline in accuracy and coverage. For example, the 2020 US Census undercounted the Latino population by 2.9 million people, while the 2022 South African census undercounted overall population by up to 31%. The UN estimates that one in three Africans were not included in the 2020 census.
The authors suggested that the COVID-19 pandemic disrupted traditional house-to-house interviews and impacted funding. The team also highlight a growing distrust in national governments, with some communities fearing immigration-related law-enforcement will use their data against them, and others worried about the threat of data leaks and cyber-attacks. “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,” said co-author Dr Dana Thomson from Columbia University.
It’s not all bad news, however. New technologies, such as AI-derived building footprints from satellite images, can support the planning and implementation of censuses and potentially reduce costs. There have been some recent successes using this method in multiple countries that WorldPop has supported, such as the Democratic Republic of the Congo.
“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,” said Professor Andrew Tatem, a coauthor of the paper. “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.”
Espey JM, Tatem AJ, Thomson DR. Disappearing people: A global demographic data crisis threatens public policy. Science. 2025 Jun 19;388(6753):1277-1280. doi: 10.1126/science.adx8683. Epub 2025 Jun 19. PMID: 40536961.