From The Hole in Our Collective Memory: How Copyright Made Mid-Century Books Vanish, Rebecca J. Rosen, the Atlantic website.
Last year I wrote about some very interesting research being done by Paul J. Heald at the University of Illinois, based on software that crawled Amazon for a random selection of books. At the time, his results were only preliminary, but they were nevertheless startling: There were as many books available from the 1910s as there were from the 2000s. The number of books from the 1850s was double the number available from the 1950s. Why? Copyright protections (which cover titles published in 1923 and after) had squashed the market for books from the middle of the 20th century, keeping those titles off shelves and out of the hands of the reading public.
Heald has now finalized his research and the picture, though more detailed, is largely the same: “Copyright correlates significantly with the disappearance of works rather than with their availability,” Heald writes. “Shortly after works are created and proprietized, they tend to disappear from public view only to reappear in significantly increased numbers when they fall into the public domain and lose their owners.”
…Heald says that the WorldCat research showed, for example, that there were eight times as many books published in the 1980s as in the 1880s, but there are roughly as many titles available on Amazon for the two decades. A book published during the presidency of Chester A. Arthur has a greater chance of being in print today than one published during the time of Reagan.
Check out the graphs back at the article, which makes it pretty clear — books that are in copyright but older than a decade or two are largely inaccessible to readers.
(Well, except perhaps via libraries, those pre-internet hubs of ‘file sharing’ in ways publishers would rather us not. And to the extent that ebooks are replacing print books, libraries no longer will be able to provide this service of providing access to in-copyright but out-of-print texts. )