Poli sci and department sizes
Via Henry Farrell and Chris Blattman, an article showing consistent disparities across disciplines in student-faculty rations (technically majors-faculty ratios), with poli sci consistently turning up as an extreme case of too few faculty for too many students, followed by econ and psych. As Blattman puts it, this has direct bearings on "why your economics and politics professors seem to have so little time for you."
I was going to post that, in addition to the explanations discussed in those two posts, there was likely to be convergence in absolute department sizes-- certainly, once a university has determined to maintain or create a department (thereby getting into the measurable pool in the first place), there's good reason not to follow a strict proportionality rule that allows faculty size to fall to 1 or 2. You don't want a single sabbatical to destroy the department's course offerings in a year, for example. This will skew the results away from proportionality between enrollments and faculty sizes. But then I clicked through and read the paper itself, and it covers this under "minimum effective size." I would add to the paper's discussion that there's also a considerable degree of organizational isomorphism-- the kind of thing that is a "department" has a size that's somewhat more than two and somewhat fewer than 100, and there will tend to be both functional and normative pressure keeping departments at within-a-near-order-of-magnitude similar absolute sizes, regardless of student enrollment. This, again, means that low-enrollment departments won't be allowed to shrink too far-- and high-enrollment departments won't be allowed to grow too much.
The paper's got kind of a funny-- funny strange as well as funny ha-ha-- when its authors turn to explaining the apparent departure from the economists' prediction of faculty sizes that are proportionately responsive to student demand by saying that there might be politics afoot. Really! You don't say?