It is difficult to measure exactly how many papers have been downloaded. As of January 1, 2015, we estimate that 3,173,000 papers have been downloaded, and people have visited 3,551,000 times. This is not counting downloads and visits made by “robot” readers from sites such as Google and Yahoo, and it does not count partial downloads or failed attempts to download.
Many of our readers are students and professors on the academic schedule. Readership usually dips during spring holiday, final exams and summer vacation in U.S. and European universities.