A premature diagnosis of cost disease?

After cuts in state funding, the most popular theory to explain the rapid increase in college tuition seems to be cost disease:

Baumol's cost disease (also known as the Baumol Effect) is a phenomenon described by William J. Baumol and William G. Bowen in the 1960s.[1] It involves a rise of salaries in jobs that have experienced no increase of labor productivity in response to rising salaries in other jobs which did experience such labor productivity growth. This seemingly goes against the theory in classical economics that wages are closely tied to labor productivity changes.

I've never felt entirely comfortable with the way this explanation fits (or fails to fit) the data. It always seemed to me that the tremendous increase in very low-priced adjunct labor would more than balance out the flat productivity gains.

If this post by Paul Campos of Lawyers, Guns and Money is accurate, the theory is even more at variance with the facts that I thought. ( Campos also has some interesting things to say about the drop in state funding explanation.)

Everyone is aware that the cost of going to college has skyrocketed since [fill in any date going back to the middle of the last century]. Why has this happened? This post is about one possible explanation, that turns out not to have any validity at all: increases in faculty salaries. In fact, over the past 40+ years, average salaries for college and university faculty have dropped dramatically.

Salaries have increased, sometimes substantially, for a tiny favored slice of academia, made up of tenured professors at elite institutions, some professional school faculty (business, law, medicine), and most especially faculty who have moved into the higher echelons of university administration. Such examples merely emphasize the extent to which the economics of the New Gilded Age have infiltrated the academic world: the one percent are doing fabulously well, and the ten percenters are doing fine, while the wretched refuse of our teeming shores will adjunct for food.

Numbers:

Average salary for all full-time faculty in degree-granting post-secondary institutions (this category includes instructors and lecturers, as well as all ranks of professors) in constant 2012-13 dollars:

1970: $74,019

2012: $77,301

These figures, of course, give a very incomplete picture of the economic circumstances of the actual teaching faculty in America’s institutions of higher education.

One of the more astonishing statistics regarding the economics of our colleges and universities is that, despite the fantastic increase in the cost of attending them, there are now on a per-student basis far fewer full-time faculty employed by these institutions than was the case 40 years ago. Specifically, in 1970 nearly 80% of all faculty were full-time; by 2011, more part-time than full-time faculty were employed by American institutions of higher learning (note that the former category does not include graduate students who teach).

While comprehensive salary figures for part-time faculty aren’t available, it’s clear that their salaries are on average vastly lower than those of full-time faculty (and of course when it comes to who does the bulk of the actual teaching at many schools, the designations “full-time” and “part-time” have a distinctly Orwellian flavor). If we assume that “pat-time” faculty earn one-third as much as their full-time counterparts — and this seems improbably optimistic, given that the average compensation for part-time faculty for teaching a three-credit course is around $2,700 — that would mean that in 1970 average salaries for college and university faculty were nearly 30% higher, in real dollars, than they are today.

This an astonishing figure, given that, in the last 40 years, tuition at private colleges has more than tripled, while resident tuition at public institutions has nearly quadrupled.