E-prints and journal articles in astronomy: a productive co-existence

Are the e-prints (electronic preprints) from the arXiv repository being used instead of journal articles? We show that the e-prints have not undermined the usage of journal papers from the four core journals in astrophysics. As soon as the journal article is published, the astronomical community prefers to read it and the use of e-prints through the NASA Astrophysics Data System drops to zero. This suggests that most astronomers have access to institutional subscriptions and that they choose to read the journal article. In other words, the e-prints have not undermined journal use in this community and thus currently do not pose a financial threat to publishers. Furthermore, we show that the half-life (the point at which the use of an article drops to half the use of a newly published article) for an e-print is shorter than for a journal paper.