An anonymous reader writes: A new study of books and music for sale on Amazon shows how copyright makes works disappear. The research, available at http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2290181 is described in the abstract: "A random sample of new books for sale on Amazon.com shows three times more books initially published in the 1850’s are for sale than new books from the 1950’s. Why? A sample of 2300 new books for sale on Amazon.com is analyzed along with a random sample of 2000 songs available on new DVD’s. Copyright status correlates highly with absence from the Amazon shelf. Second, the availability on YouTube of songs that reached number one on the U.S., French, and Brazilian pop charts from 1930-60 is analyzed in terms of the identity of the uploader, type of upload, number of views, date of upload, and monetization status. An analysis of the data demonstrates that the DMCA safe harbor system as applied to YouTube helps maintain some level of access to old songs by allowing those possessing copies (primarily infringers) to communicate relatively costlessly with copyright owners to satisfy the market of potential listeners.