[notahacker]

The description of this suggests the analysis is a lot less plausible than the actual figure:

- Birthrates are assumed to fall linearly all the way to zero, despite an abundance of reasons why that's obviously not likely to be the case

- If I'm reading it correctly, countries' birth rate declines are estimated as a discrete property of arbitrary HDI labels rather than a function of actual HDI score. Which in practice means that minor threshold differences decide whether birthrates in a country to fall sharply across one decade and less sharply in another

- Small islands are given equal weight to China and India in gauging an HDI-bracket's average birth rate

- The HDI brackets aren't even copied correctly, and thus many ultra wealthy territories like Bermuda and Gibraltar are placed in the "low HDI" bracket. That probably means the model massively underestimates the YoY decline in birthrates in low development countries (which I suppose at least works in the opposite direction to incorrect assumptions made about birthrates dropping to zero)

- There's really no justification at all for projecting a death rate that varies between ~1 and ~15 per 1000 as a uniform 8 per 1000, especially not when data on population age distributions and life expectancies exists. (The only saving grace is that it isn't that far from the figure for India and China which have a disproportionate effect on the model)