In a new paper, a group of MIT researchers argue that science is producing PhDs in far greater numbers than there are available tenured jobs for them to fill.

The authors, engineers Richard C. Larson, Navid Ghaffarzadegan, and Yi Xue, start out by noting that

The academic job market has become more and more competitive nowadays, less than 17% of new PhDs in science, engineering and health-related fields find tenure-track positions within 3 years after graduation.

But why? Are we simply producing too many PhDs nowadays? Larson et al. approach this question by borrowing a concept from epidemiology: R0 (R nought), known as the basic reproduction number. In the context of an infectious disease, R0 is the average number of people who are newly infected by the disease by each existing patient. Influenza, for example, has an R0 of about 1.2 1.6. If R0 is greater than 1, the disease will spread exponentially.

Larson et al. define the academic R0 as the total number of PhD graduates created by (supervised by) the average tenure-track academic (i.e professor) over the course of the professors career. If this number is greater than 1, more PhDs will be created than there are tenured posts for them all to occupy assuming that the number of tenured professors is roughly constant.

It turns out that the R0 at MIT is approximately 10. MIT produces some 500 PhDs per year, and it has 1000 faculty. So each faculty member produces 0.5 students per year. Since the average faculty members career at MIT spans 20 years, each faculty member produces 10 PhDs in total.

By using the same approach, Larson et al. say that the R0 across the whole field of engineering in the USA is 7.8. But this varies across specialties. Mining and Architectural Engineering both have a sustainable R0 of just 1, while Environmental Engineering (ironically) is the gas-guzzler of the bunch, with an R0 of 19.

Larson et al. conclude that

Our back-of-the-envelope calculations suggest that R0 for the entire engineering field is 7.8, which implies that in a steady state, only 1/7.8 (i.e. 12.8%) of PhD graduates in engineering can attain academic positions in the USA the system in many places is saturated.

In demography, any living population eventually meets a ceiling of limited resources. Similarly in academia, the growing PhD population will eventually hit the natural ceiling of limited tenure-track positions. In some fields, it already has hit that limit the oversupply must move to nonacademic positions or be underemployed in careers that require lesser degrees.

Read more:
Does Science Produce Too Many PhD Graduates?