Richard Vedder and co-authors analyze the numbers.

More than one-third of current working graduates are in jobs that do not require a degree, and the proportion appears to be rising rapidly…60 percent of the increased college graduate population between 1992 and 2008 ended up in these lower skill jobs, raising real questions about the desirability of pushing to increase the proportion of Americans attending and graduating from four year colleges and universities.

I have reported on this research before, but the link is to a longer paper. The paper includes interesting references, including Edwin S. Rubinstein writing in 1998 on a forecast for job trends. It turns out that the Department of Labor at the time foresaw that jobs requiring on-the-job training, rather than a college education, would increase. And, of course, that does not even account for the jobs, such as physical therapists, that only require a college education due to licensing laws.