Two is not always better than one.

A new study shows that if you combine two disciplines in your dissertation, you can expect to earn less than you would otherwise in the year after finishing your doctorate.

Everyone, it seems, loves the idea of scholars interdisciplinary work. But does academe reward those — particular young scholars — who actually do it?

A new study, based on data from all people who earned Ph.D.s in 2010, suggests the opposite. In the year after earning their doctorates, those in the cohort who did interdisciplinary dissertations earned, on average, $1,700 less than those who completed dissertations in a single field. The study was conducted by Kevin M. Kniffin and Andrew S. Hanks, two postdoctoral fellows at Cornell University, and has been released by the Cornell Higher Education Research Institute.

Kniffin and Hanks used data from the Survey of Earned Doctorates, and focused on the more than 26,000 people who earned doctorates that year who are U.S. citizens. The income of new Ph.D.s, of course, varies by such factors as discipline, whether postdoctoral employment is within academe or outside it, and whether the first job after the Ph.D. is a postdoctoral fellowship. Kniffin and Hanks came up with their $1,700 gap by controlling for discipline, age, gender and ethnicity. They reasoned that because some disciplines are more likely than others to produce new doctorates who seek employment outside academe, they could address various differences in post-graduation patterns of various new doctorate holders.

The Survey of Earned Doctorates specifically asks if new Ph.D.s did a multidisciplinary dissertation, so that information was readily available for the study.

In non-academic life, Kniffin and Hanks write, there is evidence that employers reward people who can draw on varied experiences and areas of expertise. For for those who prepare for employment (in academe or in some cases out of academe) with a Ph.D., that does not appear to be the case. “The current value system in academia clearly imposes a cost on boundary spanning,” they write.

Via email, Kniffin said that interdisciplinary scholars may face a range of challenges in getting the best job — especially at the beginning of their careers. “For a department that’s hiring someone whose job will be to teach Intro courses, then certainly it seems plausible that an interdisciplinary dissertation could be viewed as a liability or, at least, a distraction when people are reviewing applications for a new hire,” he said.