We have covered the topic of the population a few times already. Parameters such as fertility per woman and population growth rates started their downward journey for most countries some time ago. Take the top four populous countries in the world, China, India, the US and Indonesia.
| China | India | US | Indonesia | |
| Population growth rate (%) (1963) | 2.46 | 2.06 | 1.44 | 2.66 |
| Population growth rate (%) (2019) | 0.355 | 1.01 | 0.455 | 1.1 |
| Child per woman (1963) | ~6 | 5.88 | 3.35 | 5.63 |
| Child per woman (2021) | 1.66 | 2.22 | 1.89 | 2.24 |
8 Billionth Child
But today is a special day. The United Nations considers 15th November 2022 as the official day of the birth of the 8th billionth child. It took 11 years for the number to go from seventh billion to eighth. And it will take another 15 years to reach ninth. Based on the UN estimates, the global population will peak somewhere between 10 and 11 billion.
The question is: how reliable is this UN estimate? The answer comes from a study published in 2001 by Nico Keilman. The publication explored 16 sets of population projections by the UN between 1951 and 1998 and concluded that they did a decent job of predicting population. Following are the Mean absolute percentage error (MAPE) of those studies.
| Base Year | MAPE |
| 1950I | 12.6 |
| 1950II | 11.2 |
| 1950III | 3.5 |
| 1960 | 1.8 |
| 1965 | 2.2 |
| 1970 | 1.5 |
| 1975I | 0.6 |
| 1975II | 0.2 |
| 1980I | 0.2 |
| 1980II | 0.2 |
| 1985I | 0.9 |
| 1985II | 0.9 |
| 1990I | 1.1 |
| 1990II | 0.6 |
| 1995I | 0.4 |
References
Population forecast: Gapminder
8 billionth child: BBC
The world’s population has reached 8 B. Don’t panic: The Economist
Keilman, N., Population Studies, 2001, 55, 149
