Rice and Michigan State validate a five-part measure of drift from a scientist's PhD field

The measure keeps the doctoral field and uses it as the origin. Five items ask how closely a scientist's current professional life still lines up with that field: their department, their primary professional association, where they publish, how peers perceive their discipline, and how they identify themselves ^[7]. The score puts them on a continuum from the core of a discipline out to its frontier and past it ^[8]. The phys.org account frames the problem with a scientist who took a physics doctorate 25 years ago, now works on climate change, publishes in interdisciplinary journals and calls herself a climate scientist ^[22].

Three of those five items could in principle be read off records ^[7]. The other two are perceptions, and all five came from a questionnaire returned by 4,113 tenure-system science faculty at 83 US research universities ^[5], about 50 respondents per campus ^[1].

Of those respondents, 16.6% named a current discipline different from the one on their doctorate, roughly 683 people ^[9][2]. Around 83% stayed inside their original nominal label ^[9]. The 83% are the harder case. Among faculty who never formally switched, the scale still separated those whose work remained tied to the original field from those whose work had moved ^[10].

"Scientists don't necessarily stay in the same intellectual box throughout their careers," Pizzo said ^[11]. The survey found broader affiliation among faculty further out from graduate school, and the association was stronger among those with more cross-disciplinary research experience ^[12]. "Cross-disciplinary research experience was especially strongly associated with broader disciplinarity," Pizzo said ^[15].

That result is an association measured across faculty at different career stages, so it does not show individuals moving. Scientists who finished a doctorate 25 years ago trained in a different departmental world than those who finished five years ago. The survey also cannot say whether cross-disciplinary work pushes people toward a boundary or whether people already near one take that work on.

Pizzo and McCright's review of earlier surveys found disciplinary affiliation measured with only one or two indicators ^[17]. Researchers who study scientists have long grouped them by field of highest degree, by department, or by the discipline they name ^[18], and the authors report that those approaches miss real differences among people who technically share a field ^[19]. "Academic disciplines are useful categories, but they aren't impermeable containers," said McCright, a sociologist at Michigan State and the paper's corresponding author ^[14][3].

The measure appeared in PLOS One, and the use the authors name is research on scientists: studies of how a scientist's background shapes their views, behaviors and approaches to research ^[4][20]. Whether grant panels and bibliometric field classifications carry the same error is not something a survey of faculty self-reports can settle ^[5].