An average of nearly 10,000 copies of every book published is downloaded from filesharing sites, according to a new study by Attributor.  The study examined a sample of 913 popular titles and 25 filesharing sites.  Fiction titles were actually among the least affected titles, with an average of around 6,000 copies downloaded per title; business and investing titles were the category most likely to be illegally downloaded, with over 13,000 per title. 

The top two filesharing sites, and, each accounted for around a third of downloaded titles, with the #3 site,, accounting for a much lower 7.4% share of book downloads.

Extapolating to the entire U.S. book market, the study estimated that the illegal downloads represented between $2.75 and $3 billion worth of content, equivalent to around 10% of the market.  Unaddressed is the question of how many of those copies actually represented a willingness to buy that was diverted to downloading, or whether, as some have argued, the increased exposure from the downloads actually contributed to increased sales.