In recent discussions of how to shorten the time it takes to complete Ph.D.s (a pressing concern in the humanities, since many students take longer than a decade to finish), some have speculated that a key reason for the lengthy time to degree in recent years has been the terrible job market. Grad students see how dismal the job market is, the theory goes, and suddenly there is no rush to finish that last chapter or schedule a defense.

This theory is half-right, according to new research released by the Cornell Higher Education Research Institute.

The study -- by Jeffrey A. Groen of the U.S. Bureau of Labor Statistics -- found that that the impact on time to degree in the humanities and social sciences is seen three to six years after the job market changes in various academic disciplines. This suggests that those who delay completion due to the job market are those who are in the middle or just starting their graduate programs, and that they somehow adjust their timetables. (Or the impact may be on the professors who advise grad students, but the shifts in pressure they put on Ph.D. candidates to finish would appear directed at those just starting, not those nearing the finish line.)

Groen writes that a good understanding of these issues is key to efforts to help graduate students finish up more speedily. There is huge variation among disciplines in how long it takes to finish, and variation within disciplines. Groen notes that Ph.D. education is unlike various forms of professional education, where there are established norms of, say, four years for an M.D. or three for a J.D.

“The open-endedness of doctoral education allows doctoral students the opportunity to adjust their completion decisions to match the labor market,” he writes. And that in turn has led to the belief that students slow down completion if they see a bleak job market. But, as Groen notes, there was (prior to this study at least) “no credible evidence that [time to degree] is related to labor demand for new Ph.D.s.”

Groen based his study on data from the Survey of Earned Doctorates, a national database supported by the National Science Foundation. He studied the cohorts of those who earned doctorates from 1975 to 2008 in seven disciplines: anthropology, classics, economics, English, history, philosophy and political science. Those fields were not identical, in the years studied, for time to completion. Economics had the shortest mean time to degree, at just over 8 years, while anthropology, English and history were all over 11 years.

To measure labor demand, Groen used the job notices of the relevant disciplinary associations. He acknowledges in the paper that this is an “imperfect” measure that does not account for every opening. Still, most people who track job markets within disciplines say that these listings serve as a good, broad measure of trends.

The conclusion? Groen writes: “The results indicate that although current job listings are not associated with the probability of completion, job listings in prior years are associated with the probability of completion…. [T]he presence of an association with listings in prior years suggests than an effect operates through choices made by students earlier in their graduate programs, such as the dissertation topic and the research plan for the dissertation.”

Groen found the typical time lag for impact to be three to six years after a job market shift, with the strongest impact evident five years after a shift. The impact was most evident in anthropology, history and political science.

Several efforts are ongoing to cut time to degree for Ph.D. students. At the annual meeting of the Modern Language Association this month, a committee presented ideas for revamping the dissertation, and the president of the association called for time to degree rates to be cut in half.