“But in general, [economist Wendy Stock of MSU-Bozeman] said, she was struck by how little her study was able to explain. Most of the variation in time-to-degree, she said, must be related to factors that can’t easily be measured, like students’ motivation and creativity, and faculty members’ mentorship styles.”
Ah, economists. Motivation, creativity and mentorship as ‘unmeasurables’. But, of course, it is an interesting and important question (at least, to me): What would it take to speed the overall pace of Ph.D. completion?