Is This What Makes America Strong ? - There Are 5,000 Janitors in the U.S. with PhDs

My uncle the lobsterman has a PhD. But that doesn’t count since he got it when he was 74, and then in lobstering (marine biology, and his dissertation was on lobsters).

There are 18,000 parking lot attendants in the U.S. with college degrees. There are 5,000 janitors in the U.S. with PhDs. In all, some 17 million college-educated Americans have jobs that don't require their level of education. Why?
The data comes from a the Bureau of Labor Statistics, and can be seen here in handy, depressing chart form:

At the Chronicle, where the above chart was posted, Richard Vedder argues that maybe we place too much importance on higher education, citing a new study by the National Bureau of Economic Research:

This week an extraordinarily interesting new study was posted on the Web site of America's most prestigious economic-research organization, the National Bureau of Economic Research. Three highly regarded economists (one of whom has won the Nobel Prize in Economic Science) have produced "Estimating Marginal Returns in Education," Working Paper 16474 of the NBER. After very sophisticated and elaborate analysis, the authors conclude "In general, marginal and average returns to college are not the same." (p. 28)
In other words, even if on average, an investment in higher education yields a good, say 10 percent, rate of return, it does not follow that adding to existing investments will yield that return, partly for reasons outlined above.

Whatever some eggheads work out "college" to mean for people on paper can't really take into account the experience of going to college, but the numbers are pretty surprising nonetheless. So next time you see a custodian scribbling the proof to some unsolvable math problem on a chalkboard after hours, well, you know.