Writing About Population Projections: Beware

by Carl Haub, senior demographer, Population Reference Bureau

It’s quite common to see reports such as “The United Nations projects that world population will be 9.3 billion in 2050,” a perfectly true statement. Many readers will most likely take that at face value and move on. But they should be asking questions! There are over 200 countries in the world with birth rates from 1.1 children per woman (in Taiwan) to 7.6 (in Niger). In most of those countries, it is the future course of the birth rate that will largely determine population size. The projection of 9.3 billion is just the sum of all the country-level population projections. What should those readers ask? For starters: What does the United Nations assume will happen to all those birth rates over the next few decades?

For countries with high birth rates, it has long been the convention to assume that the total fertility rate will decrease steadily to two children per woman (or fewer); and that essentially is what has happened in today’s wealthier, low-birth-rate countries such as Germany, South Korea, and Spain. The UN, the U.S. Census Bureau International Programs Center, and many national statistical offices make this assumption. The UN is careful to point out that its projections assume that the use of family planning will spread, resulting in lower birth rates. It is also often assumed that very low birth rates in industrialized countries will “recover” and rise. Readers almost never know these assumptions.

As one might imagine, the real world often doesn’t cooperate. Take, for example, Nigeria. The UN projects that Nigeria’s population will rise from 170 million today to 390 million in 2050 and then on to 730 million in 2100—although that’s a long, long way off. But what does the UN assume about Nigeria’s birth rate? That it will decline to about 3 children per woman by 2050, from just under 6 today. But, as demographic surveys taken in the 2000s, including a very recent one, have shown, birth rate decline in Nigeria is not taking place.

The UN actually produces three major projections, not just the “medium variant” quoted here thus far. Its “constant fertility (birth rate) variant” shows what would happen if the current Nigerian birth rate were to continue unabated: 504 million in 2050 (not 390 million). No one really expects the country’s birth rate to remain at today’s level for almost 40 years, but looking at different scenarios reminds us that there is definitely more than one possible outcome for population growth.

Trying to cram all of this into a headline is, of course, a virtual impossibility, and putting too much detail into an article can be counterproductive. But explaining the assumptions from which projections result can definitely be far more informative than not doing so. Along the way, additional factors such as future death rates and trends in migration can also affect countries’ demographic futures. But that is a blog post for next month!

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