Does Science Produce Too Many PhD Graduates?

By Neuroskeptic | February 18, 2015 3:24 pm

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, the 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 (i.e. supervised by) the average tenure-track academic (i.e professor) over the course of the professor’s 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 member’s 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.

r0_academicLarson 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.

The Malthusian logic of this argument is compelling, but it makes a lot of assumptions. Firstly, it ignores international students, and academics whose careers span multiple disciplines. These issues, however, probably all cancel out at the global level.

A more fundamental problem, however, is that Larson et al.’s approach assumes that every PhD graduate wants to become a tenured professor. In fact, some (maybe most?) PhD graduates choose to leave academic research. They don’t compete for tenured jobs. Given this, the ‘steady state’ academic R0 must be higher than 1 – perhaps a lot higher.

Larson et al. note this “opting out” issue, but they don’t give any estimates for how many people opt out or what the ideal R0 must therefore be. Until we know that, we won’t know how excessive the production of PhDs is.

ResearchBlogging.orgLarson RC, Ghaffarzadegan N, & Xue Y (2014). Too Many PhD Graduates or Too Few Academic Job Openings: The Basic Reproductive Number R 0 in Academia. Systems research and behavioral science, 31 (6), 745-750 PMID: 25642132

  • Douglas Summers-Stay

    Getting a PhD in one of these fields usually means that you like doing research and want to be a researcher. But in a lot of cases, that’s easier to do in industry or (in my case) working in a government lab than at a university, where you also have teaching responsibilities. You can still explore, you can still publish papers, you can still work with graduate students.

    • Neuroskeptic

      Yes, that’s true. It’s part of the “opting out” problem that I mentioned in the post (even though people like you are not opting out of science, just opting out of tenured professorships.)

  • feloniousgrammar

    I think the problem is not enough funding for independent research, which I’m convinced we need a LOT more of.

  • Anonymouse

    Even if you stay in academia, you can just be a permanent post-doc researcher and not a professor, at least in Germany.

  • Suzanna Wood

    Very interesting analysis. Could something similar be done for post-docs? One might argue that a substantial amount of “opting-out” happens once the PhD is awarded, with those with more intention to pursue an academic career opting to take a post-doc position. What about doing the same analysis for the number of 1st post-docs per tenured academic?

    • John Licato

      Exactly right…it would be nice to see data on how many people want to go the phd->postdoc->faculty route and fail or succeed.

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  • Ed Trollope

    The R0 calculation is laughably flawed, because it would only hold true if all PhD graduates remained at MIT to “infect” further students. Calculating the R0 of a disease by first discarding from your dataset all carriers that didn’t pass on that disease is nonsense.

  • Marcus Kaiser

    Concerning opting out, I had a look at the numbers for Germany some time ago (see image below). The table contains the number of awarded PhD in 2001, the percentage of these PhDs that are interested in an academic career, and the percentage of people who will get a professorship out of the ones that are interested. Looking at the range of subjects, biology, chemistry, physics, mathematics, computer science, psychology, and engineering, chances for those that are interested in an academic career are below 15% in general and below 5% for biology and chemistry.

    These numbers do not take into account international job applicants or the recent surge in PhD numbers due to the German Excellence Initiative. So I would expect lower percentages now.

    More information (unfortunately only in German) can be found at

    • Neuroskeptic

      Thanks very much! So these results suggest that, although the majority of PhDs do not want an academic career, there are still not enough jobs even for the ones who want one?

      • Marcus Kaiser

        Yes! It also highlights differences between disciplines. Even though more maths PhDs are interested in an academic career than physics PhDs (45% vs 25%), their chances to become professor are twice as good. Presumably this is linked to the R0 value in that maths professors produce fewer PhDs than physics professors.

  • CaliforniaMC

    Context. Are people willing to move to find the career? International positions? be adaptable. Everyone wants to live in Miami and Los Angeles but, that’s probably not going to happen.

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  • oh7dp

    This is OLD news. People have been pointing this out since the 80s. Most PhD in physics, chemistry, math and bio have been heading out of the academy, often involuntarily. There have been a few bright spots from time to time in specialties, but they quickly become jammed up.

    There have been endless discussions about this and people have written about the need for “academic birth control” but nothing changes. The kids still go to grad school with hope and the schools have no financial interest in turning them away, just so they can pay higher wages to someone else. Would you?

  • reasonsformoving

    “In fact, some (maybe most?) PhD graduates **choose** to leave academic research.”

    Th operative word here being rather fishy.

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  • Vincent Granville

    I created my own independent research lab, self-funded thanks to my business activities. The irony is that despite having a PhD in statistics, I did not even need a high school degree to get hired, since I am the guy making the hiring decision. I also granted tenure to myself a while back. My research is applied and state of the art, in data science for business problems. It is published in my blog reaching out to millions of practitioners each year, rather than in obscure journals. Turnaround is much faster than in academia, and job security is very high. Salary is also multiple times that of a typical university professor. A lot of what I do is automated.

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  • ohwilleke

    Has it not occurred to the authors that many PhDs in engineering find good lifetime jobs outside academia actually doing rather than teaching. R0 of 1 might make sense a few fields of science with no practical applications, but not in fields that have economic applications in the real world.

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  • non_sig

    Maybe there are not too many PhD-students… I mean, it is (too a large degree) a matter of politics how many PhD-positions are available in comparison to other more advanced positions.
    PhD-students are cheap, so I would guess that some funding agencies would rather fund 2 PhD-student than one post-doc position (which can be about the same expenses, depending on circumstances).
    I don’t think that is very intelligent, though it might work out in some cases. But if they are would not plan this way, why is the situation like that?
    I also think that a lot of PhD-students are deciding to leave because of the outlook…

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Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.


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