Professor Steve Horwitz at Saint Lawrence University made an excellent post on income mobility a few months back. As the ranks of the lowest income quintile swell with new immigrants and 18-year-olds moving away from home, the average incomes of the people who made up the lowest quintile in 1996 had increased 90.5 percent by 2005, according to a report from U.S. Department of the Treasury.

Horwitz also offers statistics on how bottom-quintile households today have far more in terms of material consumer goods than did the bottom-quintile households of past years.

UPDATE: A professionally successful reader offers his family and career as a real-life example.

In the late 1970′s I earned just over minimum wage working full time as I struggled to put myself through school. Last year, my W-2 compensation was just over $400,000. This year, it will be just over $200,000. (Do you think the Democrats will worry over my 50% cut in pay?) My wife and I are among of those who went from the lowest income quartile to the top quartile over the course of my career.
Today, our three children are in college. They all work part time at jobs making just over minimum wage. My son provides almost all his own support. We help him very little financially. He makes up one of the “households” in the lowest income quartile…I don’t feel sorry for him. Soon, he’ll start to climb. So will most of his peers in the bottom quartile. This is not a static situation; it’s a natural progression.