Thanks for the link.

These stats just backup what I've always heard - the top 10%, 1%, whatever, is not static. Neither is the bottom 10%. Many people usually start their careers at the bottom (i.e. college student working part time) and then eventually make it into the middle class and plenty make it further than that. Of course, some never make it out of poverty.

I've heard otherwise that this mobility (which nobody denies exists) is about the lowest it has ever been and growing more static. I'm sure some searches about social mobility stats would bring up lots of stuff.

If you do a google search on mobility, you'll find papers that say a whole lot of different things - some that say it's gotten worse, some that say it's gotten better.

The biggest problem is data. It's not that great.

What are these numbers actually taken from? I'm betting the vast majority of this is counting the sale of a home or a one-time windfall (e.g. small inheritance, gambling winnings) as income for "a year", but I'm not going to buy the book just to see.

Russ Roberts has a fairly thorough treatment of composition effects impacting income statistics: https://medium.com/@russroberts/do-the-rich-capture-all-the-...