My thanks to those who pointed to Steve Lawrence's work, based on conference articles in computer science and related disciplines:
http://www.neci.nec.com/~lawrence/papers/online-nature01/ Online or Invisible?, Steve Lawrence, NEC Research Institute An edited version appears in: Nature, Volume 411, Number 6837, p. 521, 2001: http://www.nature.com/nature/debates/e-access/Articles/lawrence.html Free online availability substantially increases a paper's impact. An excerpt: "The results are dramatic, showing a clear correlation between the number of times an article is cited and the probability that the article is online. More highly cited articles, and more recent articles, are significantly more likely to be online, in computer science. The mean number of citations to offline articles is 2.74, and the mean number of citations to online articles is 7.03, an increase of 157%." If these dramatic results (for conference articles in computer science and related disciplines) could be confirmed in other unrelated disciplines, then the evidence would become even more compelling. Another question: has anyone obtained evidence that the impact factors for open-access journals have increased across time, in comparison with competing toll-access journals? Jim Till University of Toronto
