OA impact advantage beyond self-selection

Travis Metcalfe, The Citation Impact of Digital Preprint Archives for Solar Physics Papers, Solar Physics, Volume 239, Issue 1-2 (December 2006) pp. 549-553.  (Thanks to Michael Kurtz via Stevan Harnad.)

Abstract:   Papers that are posted to a digital preprint archive are typically cited twice as often as papers that are not posted. This has been demonstrated for papers published in a wide variety of journals, and in many different subfields of astronomy. Most astronomers now use the arXiv.org server (astro-ph) to distribute preprints, but the solar physics community has an independent archive hosted at Montana State University. For several samples of solar physics papers published in 2003, I quantify the boost in citation rates for preprints posted to each of these servers. I show that papers on the MSU archive typically have citation rates 1.7 times higher than the average of similar papers that are not posted as preprints, while those posted to astro-ph get 2.6 times the average. A comparable boost is found for papers published in conference proceedings, suggesting that the higher citation rates are not the result of self-selection of above-average papers.

From the conclusion: 

Despite the slower adoption by the solar physics community, digital preprint archives boost the citation rates of posted papers to twice the level of unposted papers, a conclusion first noted in the comprehensive study of Schwarz and Kennicutt (2004). The evidence suggests that, like many other subfields in astronomy, the citation rate is elevated from the improved visibility of the paper rather than from self-selection by authors choosing to post above-average papers. Unlike other subfields, solar physicists maintain an independent preprint archive which also boosts citation rates, though the broader user-base of astro-ph provides a larger boost.

If citation rates track the assimilation of new results by the community, then astro-ph seems to be the best single form of communication available. Editors who want to maximize the impact of their journals should encourage authors to post their preprints to astro-ph. Authors in solar physics, where astro-ph is currently underutilized, should consider the advantages that other subfields have already discovered.