How do population projections work?

It's getting crowded in here... or is it...? Image: AFP/Getty.

“Britain’s population set to grow by TWICE as much as the rest of Europe combined”, the Daily Express screamed a few weeks ago. By 2080, it warned, the UK population could hit 85m, up from around 65m at the moment.

Leaving aside the fact that by 2080 the entire Daily Express demographic will be long dead, I scoffed at the story, wondering what crazy nonsense the newspaper of discord will come up with next. But having looked into the claim, it turns out to be based on facts: the Office of National Statistics reckons that, by 2080, Britain will contain 84.6m people.

This made me wonder – how exactly was this number derived? Population projections are important, especially when it comes to issues of planning and infrastructure of the sort that CityMetric likes to cover.

Major transport projects, for example, take decades to plan and execute, and are built on timescales that would make The Vatican appear hasty. High Speed 2 is not expected to be fully operational until 2033; the Bakerloo Line extension, which has been under discussion for decades already, is currently planned for 2040 – making it likely that many of the people who are currently trying to make it happen will never get to ride on it.

But if these projects are to happen, then planners and politicians must have at least some idea of what they expect things to be like far into the future. And this starts with a population estimate: will the extra capacity be even needed? Will there be more or less people? How the hell is Transport for London supposed to know if more people will live on the Old Kent Road or in Camberwell several decades from now?

Embarrassing precedents


Unfortunately, history doesn’t suggest that we’ve ever been particularly good at projecting population changes.

In 1947, the US Bureau of the Census predicted that by the year 2000 there would be 163m people in the United States; in the event, it was 281m. Even if you take the Bureau’s top estimate, where both fertility and migration were expected to be “high”, it only predicted 200m – significantly lower than it turned out. And even if you cut the Bureau some slack about the fact that 50 years is a long time horizon to be working with, the same report also predicted that in 1970 there would be 177m Americans – still far less than the 203m there actually were.

Perhaps even more awkwardly, in 1928 Robert R Kuczynski wrote in the journal Foreign Affairs that, “At its present rate of increase, we are told, the world's population will have reached 5,000 millions [ie: 5bn] before the end of this century – 5,000 millions being at the same time the absolute maximum which the planet can sustain.”

He seemed absolutely convinced by that with Malthusian fervour. He was nearly 1bn out.

Even my favourite band, American punk rock veterans Bad Religion, called it a little wrong when they predicted in a track on 1996 album The Gray Race that the population would be 10[bn] in 2010. It was less than 7bn.

No doubt the study of populations has moved on significantly since the examples above, but it is hard to know for sure because it is literally a case of “only time will tell”. But can we anticipate just how wrong current projections will be?

This was a question that troubled researchers way back in 1991 who compared state population projections based on a number of different models. They found that there was broadly a linear correlation, which “found a very strong tendency for population forecast errors to grow approximately linearly with the forecast horizon”.

In other words, the further away you try to forecast, the more wrong you’re likely to be.

Keeping it simple

So, the big question: how exactly are these numbers figured out? Are the supposed experts just picking numbers out of the air?

It turns out that population forecasts are not particularly complex calculations,  based on assumptions relating to three sets of statistics: birth rates, death rates and migration.

A wide range: How world population changed from 1800 to 2010 (black and blue), and various models for how it could change in the future (red, orange, green). Image: Loren Cobb/Wikimedia, based on United Nations figures.

I spoke to David Voas, Professor of Population Studies at the University of Essex and he told me that:

“There are clearly limits to any 'scientific' forecasting, especially where human behaviour is involved.  The usual methods of population projection can be highly sophisticated, but basically they depend on processing a large amount of data on fertility and mortality and assumptions about the direction and pace of current trends.

“To put it another way, in stable developed societies in ordinary circumstances there's not a huge amount of uncertainty about how many people will die and how many will be born each year for the next few decades.  Of course we could be wrong – maybe people will suddenly decide that it's ideal to have three children, or only one – but these kinds of shifts don't tend to be rapid.  Similarly life expectancy will continue to rise, and we might be too optimistic or pessimistic about how rapidly, but the difference it makes to the total population is marginal.”

Essentially then, the tricky part is migration. I was curious as to how you would even begin forecasting migration. And how are potential cataclysmic events taken into account? How can you possibly predict the incidence of war, epidemic disease, and natural disasters, let alone their impact on populations? And what about the potentially transformative effects of climate change?

Professor Voas told me that demographers can estimate UK birth or death rates to within thousands or tens of thousands of accuracy. But trying to predict migration, following an event like the civil war in Syria, which is one of the big factors contributing to the current refugee crisis, is essentially “an awful lot of guesswork”.

The best laid plans

So what does it mean for us a society, and for the planners and politicians who rely on these numbers? As far as I can tell, it means that population forecasts should come with something of a health warning. The projections may be the best information we have to go on – but there is still significant room for errors.

The office of London’s mayor, at least, appears to recognise this. In a report on what it expects the capital to be like in 2050, it paints a picture of the city with a population anywhere between 9.5m and 13.4m (both figures are significantly up from the 8.6m today). The report notes the difficulty of forecasting – but it also argues that, despite huge changes in the 20th century, things like the time people spend travelling each day has remained relatively consistent. There are areas in which our guesses are at least educated ones.

Nonetheless, could we fall into the trap of giving the projections too much credence? If the London population figures are predicated on the same assumptions as many similar forecasts, then can we be sure all factors are taken into account? While fertility, death and migration figures may support the assumption that the population will rise, won’t the capital’s housing crisis at some point start forcing people away?

And is it really right to assume that, despite changes in technology, public transport usage will remain static? What about emergent technologies like video conferencing, or even future ones like virtual reality? (I reached out to TfL to ask about how it makes its projections, but sadly no one got back to me.)

For the rest of us, I think the lesson is that we should remember to look beyond the headlines and ask how the numbers on which we rely are derived – and calibrate the credibility we afford them accordingly. Predicting population changes and planning for the future is hard. It doesn’t mean that we shouldn’t do it; but it does mean that we could still get it very wrong indeed.

James O’Malley tweets as @Psythor.


In South Africa's cities, evictions are happening despite a national ban

An aerial view shows a destroyed house in Lawley, south of Johannesburg, on April 20, 2020. The city has been demolishing informal structures on vacant land despite a moratorium on evictions. (Marco Longari/AFP via Getty Images)

On the morning of 15 July, a South African High Court judge ruled that the city of Cape Town’s Anti-Land Invasion Unit had illegally evicted a man when it destroyed the shack where he was living.

That afternoon, the Anti-Land Invasion Unit was out again, removing shacks in another informal settlement.

Evictions were banned in South Africa for nine weeks, after the national government placed the country under a strict Covid-19 lockdown in late March. At present, eviction orders are automatically suspended until the country moves to a lower “alert level” and can only be carried out with a special order from a judge.

Yet major cities including Cape Town, Johannesburg and eThekwini (created through the merger of Durban with several surrounding communities), have continued to use municipal law enforcement agencies and private security companies to remove people from informal housing. In many cases those operations have been conducted without a court order – something required under regular South African law.

Around 900 people were evicted from three informal settlements in eThekwini during the eviction ban, according to the Church Land Programme, a local NGO. Its director, Graham Philpott, says it’s also aware of evictions in other informal settlements.

While evictions aren’t a “new experience” in these communities, the NGO released a report on lockdown evictions because they were “so explicitly illegal”. “There was a moratorium in place,” Philpott says, “and the local municipality acted quite flagrantly against it. There’s no confusion, there’s no doubt whatsoever, it is illegal. But it is part of a trend where the eThekwini municipality has acted illegally in evicting the poor from informal settlements.”

Evictions also took place in Cape Town and Johannesburg during so-called “hard lockdown” according to local activists. In eThekwini and other municipalities, the evictions have continued despite restrictions. In Cape Town, authorities pulled a naked man, Bulelani Qholani, from his shack. That incident, which was captured on video, drew condemnation from the national government and four members of the Anti-Land Invasion unit were suspended. 

The cities say they’re fighting “land invasions” – illegal occupations without permission from the land owner.

“Land invasions derail housing and service projects, lead to the pollution of waterways, severely prejudice deserving housing beneficiaries and cause property owners to lose their investments over night,” Cape Town’s executive mayor, Dan Plato said in a statement. (Plato has also claimed that Qholani did not live in the shack he was pulled from and that he disrobed when municipal authorities arrived.)

South African municipalities often claim that the shacks they destroy are unoccupied. 

If they were occupied, says Msawakhe Mayisela, a spokesman for the eThekwini municipality, the city would get a court order before conducting an eviction. “Everything we’re doing is within the ambit of the law,” Mayisela says. But “rogue elements” are taking advantage of Covid-19, he added.

“We fully understand that people are desperately in need of land, but the number of people that are flocking to the cities is too much, the city won’t be able to provide housing or accommodation for everyone overnight,” he says. 

While eThekwini claims to be a caring city, local activists say the evictions show otherwise.

In one case, 29 women were evicted from shacks during the hard lockdown. With nowhere to go, they slept in an open field and were arrested by the South African Police Service for violating the lockdown, Philpott says.

“These evictions are dehumanizing people whose dignity is already compromised in many ways,” says S’bu Zikode, the president of Abahlali baseMjondolo, a community organization whose Zulu name translates to “the people of the shacks”. 

“It has reminded us that we are the people that do not count in our society.”

Municipal law enforcement and private security contractors hired by cities regularly fire rubber bullets, or even live ammunition, at residents during evictions. Some 18 Abahlali baseMjondolo activists have been killed since the organization was founded in 2005, Zikode says, most by the eThekwini Land Invasion Unit and Metro Police.

(Mayisela says that if city employees have broken the law, Abahlali baseMjondolo can file a complaint with the police. “There is no conclusive evidence to the effect that our members have killed them,”  he says.)

Other Abahlali baseMjondolo activists have been killed by what Zikode calls “izinkabi,” hitmen hired by politicians. Two eThekwini city councillors were sentenced to life in prison 2016 after they organized the killing of Thuli Ndlovu, an Abahlali baseMjondolo organizer. A member of the Land Invasion Unit who is currently facing a charge of attempted murder after severely injuring a person during an eviction remains on the job, Zikode says.

South Africa’s 1996 constitution is intended to protect the public from arbitrary state violence and guarantees a right to housing, as well as due process in evictions. But for Zikode, the South African constitution is a “beautiful document on a shelf”.

“For the working class and the poor, it’s still difficult to have access to court. You’ve got to have money to get to court,” he says. 

The actions by municipal law enforcement are breaking down social trust, says Buhle Booi, a member of the Khayelitsha Community Action Network, a community group in the largest township in Cape Town.

“There’s a lack of police resources and those very few police resources that they have, they use to destroy people’s homes, to destroy people’s peace, rather than fighting crime, real criminal elements that we see in our society,” Booi says.

For him, it’s a continuation of the practices of the colonial and apartheid governments, pushing poor people, most of whom are Black, to the periphery of cities.

Around one-fifth of South Africa’s urban population live in shacks or informal dwellings, according to a 2018 report by SERI. Many more live in substandard housing. City governments maintain that the shacks destroyed during anti-land invasion operations are unfinished and unoccupied. But Edward Molopi, a research and advocacy officer at SERI, says that this claim is an attempt to escape their legal obligations to get a court order and to find alternative accommodation for affected people. 

The roots of the current eviction crisis go back to apartheid, which barred non-white people from living in cities. Between the 1940s and 1970s, tens of thousands of people were forcibly relocated from neighbourhoods like Johannesburg’s Sophiatown and Cape Town’s District Six to remote townships.

In the 26 years following the end of apartheid, deepening economic inequality and rampant unemployment have limited access to formal housing for millions of South Africans. Government housing programs have mostly focused on building small stand-alone homes, often on the peripheries of cities far from jobs and amenities.

While these well-intentioned projects have built millions of homes, they’ve failed to keep up with demand, says Marie Huchzermeyer, a professor at the Centre for Urbanism & Built Environment Studies at the University of the Witwatersrand in Johannesburg. Government-funded housing projects “will never on it’s own be enough,” she says. “It has to be accompanied by land release.”

Government policies call for the “upgrading” of informal settlements and the formalization of residents’ occupation. But “there are still very, very, very few projects” of that nature in South Africa, Huchzermeyer says. “Even if it’s an informal settlement that’s been around for 20 years, there still seems to be a political wish to punish people for having done that.” The government wants people to go through the formal process of being given a house, she says – and for them to be thankful to the government for providing it.

At the municipal level, change will require “real leadership around informal settlement upgrading and around ensuring that land is available for people to occupy,” she says. 

Despite the end of enforced racial segregation, spacial apartheid remains a factor in South Africa. There are few mixed-income neighbourhoods. Those who can afford to often live behind walls in sprawling low-density suburbs, while the poor live in overcrowded slums and apartment buildings.

The creation of the apartheid city “didn't happen by chance,” says Amira Osman, a professor of architecture at the Tshwane University of Technology. “It was a deliberate, structured approach to the design of the city. We need a deliberate, structured approach that will undo that.”

Since last fall, Johannesburg’s Inclusionary Housing Policy has required developments of 20 or more units to set aside 30% of those units for low-income housing.

The policy, which faced significant opposition from private developers, won’t lead to dramatic change, says Sarah Charlton, a professor at the Centre for Urbanism and Built Environment Studies, but it is “an important and significant step.”

Zikode isn’t optimistic that change will come for shack dwellers, however.

“People in the high positions of authority pretend that everything is normal,” he says. “They pretend that everyone is treated justly, they pretend that everyone has homes with running water, that everyone has a piece of land – and hide the truth and the lies of our democracy.”

Jacob Serebrin is a freelance journalist currently based in Johannesburg. Follow him on Twitter.