Having a "clubby" culture is one explanation, but another factor could be that the NYRB just gets very high profile contributors. For example Zadie Smith has written essays for the NYRB, while also being the subject of reviews. Does this mean Zadie Smith is a part of the club? Or that NYRB is just able to get high profile authors like Smith to write for them?
I'm sure you could run the same experiment with e.g. prestigious math journals. There is probably a significant overlap between authors and reviewers.
I'm sure you could run the same experiment with e.g. prestigious math journals. There is probably a significant overlap between authors and reviewers.