8 billion and counting: How accurate are population estimates?

While Canada’s population counts and estimates are cross-referenced with precision, countries like India, Afghanistan and Lebanon are held back from achieving any up-to-date population counts at all (Getty Images/ Danny Lehman)

World Population Day has been marked every July 11 since 1987, when humanity hit the five-billion population milestone.

Canada’s own population just broke the 40-million mark, according to the Statistics Canada population clock, and the United Nations predicts that the total number of humans on the planet reached a whopping eight billion in November last year. But how accurate are these estimates?

“Highly accurate,” says King's University College at Western University professor of demography Don Kerr. At least that’s the case for Canada and the other G7 countries, whose advanced economies allow them to maintain excellent birth, death and immigration records. When it comes to some of the world’s other countries, the United Nations is navigating decades-long census delays, unreliable registries, or even a total absence of any population reporting at all. The latest margin of error for the world population estimate is plus or minus two per cent, compared to Canada’s rather precise 0.3 per cent.

AIMING FOR PRECISION

Canada’s accuracy is achieved by “an enormous level of demographic expertise at Statistics Canada,” says Kerr. “Canada’s five-year census is a luxury,” he explains. Since most countries have 10-year censuses at best, the Canadian system allows for a tighter margin of error.

While Canada’s population clock is modelled according to last year’s trends, the country’s real population measures are the demographic estimates released by Statistic’s Canada’s Centre for Demography on a quarterly and annual basis.

“One of the main reasons for their accuracy,” says Laurent Martel, director of the Centre for Demography at Statistics Canada, “is to fulfill the ‘Federal-Provincial Fiscal Arrangement Act’ used by Finance Canada to distribute annual transfer payments to the provinces and territories.” The demographic estimates are included in a formula to determine how that $88-billion fund is divided, he says.

As a major driver for the Canadian economy, it is imperative that the accuracy of the estimates be evaluated and maintained.

“We benchmark our demographic estimates on each census,” Martel explains, “to monitor accuracy on a five-year basis, and the numbers are very close, proving their high quality.”

Kerr agrees. “Canada also has very accurate estimates of census coverage error, and when the difference between the estimate and the results of the most up to date census is calculated, it typically comes in around 0.3 per cent every five years,” he says.

Canada’s demographic estimates for the first quarter were released at the end of June, and the Canadian population as of April 1, 2023, was 39.8 million, just shy of the population clock’s milestone two months later. This number is still based on data from the 2016 census, but demographic estimates using the 2021 census will be released in September 2023.

WORKING WITH AN INCOMPLETE PICTURE

When it comes to global population estimates, “152 out of 237 countries reporting to the United Nations had a population census or population registrar as recent as 2015,” Kerr explains.

While Canada has begun working with its 2021 census, other countries are experiencing setbacks. “India, the world’s largest country, with an estimated population of 1.4 billion, is still trying to complete a 2020 census that was held up by logistical problems from the COVID-19 pandemic,” says Kerr.

For Nigeria, the largest country in Africa, the UN is working with a 2006 census. The last time Afghanistan had a census was in 1979. For Lebanon, it was 1932.

Patrick Gerland, the UN’s chief of population estimates, confirms the difficulty in producing an accurate number in some cases. “The political situation of a country like Lebanon has prevented a census,” he says. “Likewise, the Democratic Republic of Congo hasn’t been able to do a census since 1917.”

For countries torn by war and political unrest, the UN relies on limited data and assumptions must be made. “This includes humanitarian situations, like those in Syria and Yemen,” says Gerland, “because you have millions of displaced people and refugees.”

The factors included in the UN’s margins of error vary tremendously by time and place. “In some countries there is a period of relative dysfunction which eventually changes to a more peaceful recovery phase,” says Gerland.

For example, China ended its one-child policy in 2016, but up until that point, many children were not being reported out of fear of penalty. “In this case, the only way to figure out how many children were alive in China was to wait until they grew up,” he says. Eventually, they appear in both the census and the education statistics, so there are two independent data sources to work with, enabling more accurate projections.

On global population estimates, Martel thinks the UN is doing outstanding work regardless of the large margin of error. “When providing either population estimates or population projections, they are putting in a lot of effort to do the best job possible,” he says.

Nevertheless, there are limits to what is possible. As Kerr puts it, “the UN has the best number available, but estimating that we hit the total of eight billion people last November is highly uncertain. It could have happened in 2021, or even 2020. Perhaps even sometime this year. Or it might not happen till next year.

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