I feel like there's a seam in this article. It starts talking about elevators, then goes to apartments. While it's semi-natural to assume $NumElevators is proportional to $numAptBuild, it strikes me as odd that a place that would probably have a significant amount of old construction would have fewer elevators, and older countries would have more old construction. As such, I would more expect the situation to be like, say, Boston, with a lot of new buildings that have nice elevators, and a lot of older, 4-6 story buildings that are entirely walk-ups.