Skip to main content

Population Projections: Breaking Down the Assumptions

Although the pace of world population growth has declined, it has not stopped and future projections remain uncertain. Further, the amount of uncertainty is significant: The difference between the United Nation’s high and low estimates for 2050 is 2.5 billion people. The assumptions that go into them are therefore very important to understand.

Date & Time

Jun. 5, 2012
12:00pm – 2:00pm ET


5th Floor, Woodrow Wilson Center
Get Directions


“The seventh billion [person] was added in 12 years, and that could be the story for the eighth billion – and that gets people who think that growth has stopped,” said Carl Haub, senior demographer at the Population Reference Bureau. Haub was joined by Hania Zlotnik, former director of the UN Population Division, and Rachel Nugent of the University of Washington’s Department of Global Health on June 5 to speak about the assumptions behind the UN population projections. While each of the panelists noted the utility of projections, they also cautioned against seeing them as inevitable.

Meeting the Projections

As a former top official in the UN’s Population Division, Zlotnik spoke about how much is riding on the projections. “The experts tell me that to feed nine billion people, living better than the standards of living that we have today, one needs to increase agricultural production or all the production of food by about 70 percent and that is a challenge, but it might be feasible. But if the numbers go higher…I think it’s impossible,” she said. 

The medium variant projection by the UN that gets the world to that nine billion figure is not a given – it builds in expected action on and improvement of many demographic indicators. Zlotnik pointed to the global unmet need for family planning, for example, which “is especially high in the high fertility countries,” and suggested that the current rate of increase in contraceptive use is insufficient. 

She calculated the number of years it would take many of these countries to meet their unmet need at their current rate of uptake and found “the number of years for a lot of these poorer countries that have high fertility would be very long – 40 years, some of them, 80 years, 100 years – because the increased contraceptive prevalence has been so small.” At that rate, population growth in these countries will far surpass the UN medium variant.

The perception that population growth is no longer an issue contributes to the problem, Zlotnik said. People see that only 18 percent of the world population lives in countries with high population growth and assume “there’s no longer a population problem.” But she emphasized the power of exponential growth, arguing that even a small proportion growing at a rapid rate can have a large impact. 

Questioning Assumptions

Haub pointed out several instances where assumptions in the methodology behind the projections create uncertainty. 

For example, there is a lack of data in many low-income countries. “A date, let’s say 2000, 2005 – it’s the past, but it may be a projection. It may be based on a census in 1990,” he said. If it’s wrong, that error may not be corrected until another census, but it will still be relied on for country-level projections. 

He also noted that certain assumptions about desired family size sometimes do not bear out on the ground. One of the key methods to slowing population growth is to provide women and couples with themeans to choose how many children they wish to bear. But in many fast-growing countries, women wish to have large numbers of children. In Niger, for example, women say their ideal family size is over nine children. Such women are less likely to use contraception, no matter how accessible it is, as they value larger families.

“It has been – I guess conventional is a good word – to assume that birth rates are going to come down the way they did in the rich countries,” Haub noted. But there has been a “stall” for many developing countries, which he suggests is caused by fast initial uptake from urban women followed by much slower uptake by rural women. These dynamics, however, are relatively new and therefore are not always well incorporated into current projections.

The Economic Impact of Population Changes

While Haub and Zlotnik looked at the assumptions made before the projections are made and the importance and means to reach these projections, Nugent focused on the economic implications of lower fertility and the demographic transition.

She suggested that increased control over fertility can positively impact a country’s economy. Women are given the opportunity to “invest their time in acquiring skills and investing time in the labor market and that affects their earnings…[and] their ability to control resources and make decisions within the household” as they spend less time caring for children, she said.

The labor market changes as well, as fewer children are born into a given generation. This can reduce “demand on economic resources [and] demand on environmental resources,” and the increased investment in human capital allowed by smaller family sizes can lead to a healthier population.

Nugent concluded by pointing out key areas of intervention most likely to decrease both fertility and mortality and allow countries to reap the positive economic benefits of fertility decline. She suggested a focus on “complementary investments in education and health,” especially with regard to “poor and marginalized populations,” which can in fact impact the country as a whole. Finally, she recommended focusing on proven “evidence-based programs [and] service-delivery programs.”

Educating Policymakers

Each of the panelists cautioned against relying on population projections without taking action to make them come true. 

“Maybe the best thing to do if you’re giving a presentation is to show the UN’s constant fertility variant first and scare people half to death and then say, ‘but if 117,000 things go right, [the medium variant projection] is what will happen,” said Haub, addressing the common tendency to view the UN projections as destiny. 

Similarly, Nugent warned against viewing the demographic transition as inevitable. “There’s a certain sense… that [the demographic dividend] is kind of an automatic thing that happens, and that really has to be addressed,” she said, adding that “it’d be quite interesting to show some scenarios of what would need to be done…in order to get some benefits from that dividend.” (See also Elizabeth Leahy Madsen’s recent article about this very topic.)

Zlotnik reiterated that the UN does not in fact know what the future will bring. “It’s not that we know what the world is going to do, but we hope that [the projections] will get the message out – if this doesn’t happen, you’re in trouble.”


Hosted By

Environmental Change and Security Program

The Environmental Change and Security Program (ECSP) explores the connections between environmental change, health, and population dynamics and their links to conflict, human insecurity, and foreign policy.  Read more

Thank you for your interest in this event. Please send any feedback or questions to our Events staff.