There are some numbers floating around the internet, allegedly drawn from Publishers Weekly (but referencing a now-defunct link to a PW Daily installment), that show the number of publishers over time starting in the late 1940s.  The numbers are intriguing, however, because when they are charted they exhibit an exponential growth curve.

Of course, there is a legitimate question as to how many of the later “publishers” are actually one-off enterprises set up to sell a single author’s book or set of books, in which case an apples-to-apples comparison might show a more reasonable growth curve.  For example, PW’s 2002 numbers show that the big five New York publishers accounted for nearly half of the market, while Andre Schiffren at the Washington Post reported in 2000 that the top 20 publishers accounted for 93 percent of sales.  Perhaps the growth curve is largely about the extension of the lower margin of a very tight power law distribution.

Anyone have more reliable numbers?