seeking alpha:

Is there really a bubble in US higher education?
Today, one way or another, we’re going to find out! First, let’s define just what a bubble is:

An economic bubble exists whenever the price of an asset that may be freely exchanged in a well-established market first soars then plummets over a sustained period of time at rates that are decoupled from the rate of growth of the income that might be realized from either owning or holding the asset.

Here, we’ll consider the asset to be one year of college education at a four-year institution, whose price is given by the cost of tuition and any required fees for attendance.