A very smart student asked me a question I didn't know the answer to (19c Chinese life expectancy), then went and found the answer (under 45 until mid-20c) himself. Better, the whole site, known as the Historical Atlas of the 20th Century, by librarian Matthew White, is a real procrastinator's dream, with all kinds of demographic and political data in map forms. Great teaching materials for modernists.
He's got some interesting alternate histories, as well, including the"what if all the separtists won?" map, the"what if Australia had been colonized by Muslims like Indonesia?" map, and the"20c Middle Earth" map (including the Hobbits' Autonomous Socialist Republic of the Shire).