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.Susquehanna University, along with many other universities, emphasizes interdisciplinary. We even require all students to take an interdisciplinary course.
A couple notes:
1. Mid-career salaries may be higher for those who's dissertations emphasized interdisciplinarity.
2. Given the market for Ph.D.s is not a representative market, this doesn't necessarily translate into what happens for those with bachelor's degrees.
Those notes aside, I thought this was a fascinating result.