[SamReidHughes]

One problem with comparing those stats across nations is that having centuries of stability will make those stats look a lot worse. Right after a big event like WW II, much of your lot in the world was the result of bad luck -- there were lots more highly-capable poor people, who were likely to move up in life, or whose children were (because of inherited personality traits). A few generations later, a lot of them have moved up, and social mobility will be smaller. You'd expect Singapore to have more social mobility than white America, for this reason alone.

There are also other factors that can help or hurt, like everybody living in the same city.