The World Bank have asked themselves this question and here is what they found: almost 87 percent of their policy reports were never cited (ht Patricia Morita Sakowski).
If you're, like me too
lazy busy to read the WB report, you can check Christopher Ingraham's piece in the Washington Post.
Nearly one-third of their PDF reports had never been downloaded, not even once. Another 40 percent of their reports had been downloaded fewer than 100 times. Only 13 percent had seen more than 250 downloads in their lifetimes. Since most World Bank reports have a stated objective of informing public debate or government policy, this seems like a pretty lousy track record.
ps. If you would like to track your own citations, you could subscribe to Google Scholar Citations.