[The authors] analyzed a hand-curated set regarding 45 years’ worth of articles (5,664 total) in four top humanities journals -- Critical Inquiry, New Literary History, PMLA and Representations. They took into account each author’s college or university affiliation at time of publication, Ph.D.-granting institution and gender. Some 3,547 authors were represented, from 344 Ph.D. institutions and 721 authorial institutions.
Regarding Ph.D.-granting institutions, the top 20 percent of universities represented in the sample account for 86 percent of the articles, and the top 10 universities represented alone account for 51 percent: Ph.D.s from Columbia, Cornell, Johns Hopkins, Harvard, Princeton, Stanford and Yale Universities and the Universities of Chicago, Oxford, and California, Berkeley, wrote 2,866 of 5,664 articles.
Authors with Ph.D.s from just Yale and Harvard account for 20 percent of all articles.
Why is this not surprising? Because in many humanities fields there are no real disciplinary standards, other than what the anointed deem worthy. Philosophy suffers from some of this too, though I would be surprised if it were to the degree found in the literary fields, but perhaps that is wishful thinking.