South Africa: 4.3% more people than the UN expected in 2017 — mostly because the UN underestimated how many people already lived there
The 2017 projection for 2023: 60.6M; the UN now estimates 63.2M, 2.6M more. The bars separate the sources of this gap.
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A population projection is built from four parts: how many people live there at the start, how many will be born, how many will die and how many more will arrive than leave. The UN has since estimated each part anew, which shows where the projection went wrong. Here the total missed, mostly because of one part. the UN later put the 2015 population 1.43M higher; migration added 1.19M more people than expected.
A bar is how much one part moved the total against the projection: right means more people than projected, left means fewer; the number is the size of the move. More births and fewer deaths add people; fewer births and more deaths take them away. “2015 population higher / lower”: the UN later estimated the population the projection started from differently from what it assumed then. The last bar is the total; the parts add up to it within a small residual.
- UN 2017 projection for 2023
60.6M
- UN 2024 estimate
63.2M
- Population in 2015: in the projection → estimated now
55.3M → 56.7M
- Births 2015–2023: assumed → estimated now
9.26M → 9.4M
- Deaths 2015–2023: assumed → estimated now
4.41M → 4.53M
- Net migration 2015–2023, arrivals minus departures: assumed → estimated now
+420k → +1.61M
- Residual of the calculation
−48.1k
The UN 2017 projection for 2023 against the UN 2024 estimate. The gap is split along the population balance: the 2015 population (estimated now minus the one the projection started from), then births, deaths and net migration over 2015–2023 (estimated now minus assumed; for deaths the other way round, since more deaths mean fewer people). Residual −48.1k: rounding and the five-year periods of older projections. Chosen: a projection of at least 8 years off by 4% or more, where one part made at least 45% of the gap.
Both the projection and the current figure are UN estimates: in countries without full registration of births and deaths they come from a model, not a count.
A question for this picture
Which of these could have been known when the projection was made?