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A hidden global crisis of population undercounting threatens to undermine policies from school building to disease outbreak response, scientists have warned.
Fewer countries are carrying out comprehensive censuses while others have delayed publishing results, reflecting Covid-19 disruption, budget cuts, and falling trust in governments, researchers said in a paper published on Thursday.
Potential damage from the decline in demographic information is magnified because advances in computing and artificial intelligence have boosted the capacity to analyse and gain insights from big data sets.
The impact was likely to be “profound” because population data is the “denominator for nearly all economic and social activity”, said Jessica Espey, lead author of the paper published in Science on Thursday.
“[It dictates] where governments invest, how they invest, and, in democracies, how they allocate electoral representation,” said Espey, deputy director of the WorldPop research team at Southampton university.
Cuts in funding for statistics bodies compromise the available data and risk ‘‘large swaths of populations going uncounted and being excluded from public policy decisions,” she said.
Authorities have used censuses since ancient Roman times to learn more about the populations they govern. In the modern era, they are often done every ten years via self-reported household surveys and interviews. Work is carried out after data collection to estimate errors in coverage and content.
Countries home to 15 per cent of the world’s inhabitants failed to conduct a population and housing census during the 2020 round from 2015-2024, the researchers said. The sharp rise — up from 7 per cent during the previous round in 2010 — means that hundreds of millions of people are no longer being surveyed.
The problem is intensified because 24 countries accounting for a quarter of the world’s people that did censuses during the 2020 round had not yet published them as of July 2024, the paper said. In some cases, this was because of concerns about declining response rates and large margins of error.
An estimated one in three people from African countries were not counted during the 2020 census round, while conflicts in nations such as Lebanon, Syria and Yemen prevented or severely limited surveys there.
The data shortfalls tend to hit poorer countries hardest. Richer nations are also affected, with censuses increasingly failing to gather full information for certain demographic groups. Children are often undercounted, while research has suggested the US Latino population was understated by almost 5 per cent in 2020 — three times the rate for 2010.
“The 2020 US Census results highlighted a systematic undercount of ethnic minority groups with the potential for impacts upon their representation, funding, and services,” the paper says.
The census coverage drop reflects a wider decline in survey participation, said Melinda Mills, a demography and population health professor at Oxford university. Budgets have been cut for national statistical offices and programmes such as the US Demographic and Health Surveys, which track population health across scores of countries, Mills added.
Countries such as the Netherlands and Indonesia have responded to the difficulties by creating population registration systems based on national identification numbers, she said. Other nations had integrated new data types, AI models and mathematical tools. “It is rarely one magic data source or solution, but rather a cocktail of data sources from government and industry partners, coupled with advanced statistical methods, that are the future,” Mills said.
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