But if I’m just using a Bayesian criterion to infer phylogeny, for example, I’m just going to cite Huelsenbeck and Rannala.  I’m not going to cite deep into the statistical literature.

In other words, it doesn’t matter how multifaceted any given academic is.  What matters is the development of stable citation communities.

Additionally, since this is an eigenfactor analysis, the volume of cross-discipline work is important.  For example, there’s a huge overlap between biology and statistics.  This isn’t because biologists are necessarily more interdisciplinary than classicists, but rather because there are significant fields of biology (phylogenetics, genomics, bioinformatics, etc) that are deeply statistical in nature and frequently involve development of new statistical inference methods.

A quick search of “phylogenetics” on Google Scholar parameterized to search only for this year yields ~20,000 papers.  A search of “genomics” for this year yields ~25,000 papers.  A search of bioinformatics yields ~27,000 papers.  These sorts of cross-discipline studies are extremely highly cited (upwards of thousands of citations per year in some cases).  Some of those connections on that figure probably represent hundreds of thousands of papers a year representing tends of millions of citation records, at the very least.  Ancient Philosophy studies simply doesn’t produce that sort of publication volume and is not central to either philosophical or classical studies in the same way, so it’s not going to show the fine-level detail you’re talking about, which represents only a handful of academics.  There’s nothing wrong with the analysis and there’s nothing wrong with Ancient Philosophy.  Don’t be so quick to judge.

Not very often, that’s how often.

And yeah, Classics really was just that isolated.  Art, too.

As for the real “dead-end” outliers like Biblical Studies or Folklore… well, these are probably the result of simply being hard-to-find or nonexistent in many universities.  Correct me if I’m wrong, but you just don’t see all that many people walking around with majors in Biblical Studies or Folklore.  Or even universities offering that list them as departments.

The data is from JSTOR.  I know that in my field many of the more interesting, experimental, and interdisciplinary-inclined journals are not represented in the JSTOR database.  It tends to have the old venerable journals, the heavyweights, which (for good or ill) tend to be conservative and move slowly.  And the majority of scholars in a given field are not publishing in them.

Some fields, like classics (and I imagine many others, like medieval studies), are in and of themselves interdisciplinary, i.e., scholars studying literature, history, language, art, archaeology, political thought, philosophy, etc… fall within one dept and share the similar/same graduate training.  Something to consider in analysis.  (For example, just try to explain the lack of a link between philosophy and classics that doesn’t exist in reality)

Also, in the humanities the book still reigns supreme in many disciplines.  So measuring with articles is not the whole picture.  I can think of several instances in which more interdisciplinary work appears in larger works, where there is more room to engage with other disciplines.