Journal Usage Half-Life :
“An analysis of article downloads from 2,812 academic and professional journals published by 13 presses in the sciences, social sciences , and the humanities reveals extensive
usage of articles years after publication. Measuring usage half life — the median age of articles downloaded from a publisher’s web site — just 3% of journals had half lives shorter than 12 months. While journal usage half lives were typically shorter for journals in the Health Sciences (median half life: 25-36 months), they were considerably longer for journals in the Humanities, Physics and Mathematics (median half life: 49-60 months). Nearly 17% (475) of all journals had usage half lives exceeding six years. This study illustrates substantial variation in the usage half lives of journals both within and across subject disciplines.”
URL : http://www.publishers.org/_attachments/docs/journalusagehalflife.pdf