Gift That Keeps on Giving, or George Will Misleads

What is the gift that keeps on giving? For social commentators, otherwise known as the chattering class (thanks G. Will), it's the concept of the social ladder. Why? Because it works for both left and right and it's so vague you can make anything of it, as George Will does here

"America's economy is so dynamic that in any five-year period, approximately 45 percent of Americans move from one income quintile to another. Twenty percent move up from the bottom quintile in any 12-month period, and 40 to 50 percent move up over 10 to 20 years."

What are the ambiguities? Let me count the ways:

1. The distinction between "income" and "wealth/assets"--the former is more variable, due to bonuses, separation pay, lottery winnings, commissions, etc. while the latter is more stable and usually more socially significant. (I've seen reports of research that says when you compare black and whites of equal family wealth, differences in test scores evaporate.)
   
2. Using quintiles, or deciles (or whatever) means that every move up is matched by a move down which is why I say it works for both left and right. Mr. Will here uses "up"; in her recent book, Bait and Switch, Barbara Ehrenreich focuses on the "down".
3. The difference between individuals and society. The modal individual in our society has an income curve that starts low, based on entry level pay in his or her occupation, then rises to a peak, then falls, rapidly or gradually depending on retirement benefits, etc. If you could visualize society over time, it's rather like seeing a school of fish: some leaping into the air, some in the water, some unseen below the surface, lots of activity and churning.