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Re: Does the arXiv lead to higher citations and reduced publisher downloads?

Kristin Antelman wrote:

Data I collected for philosophy, political science, engineering and mathematics do not support this hypothesis that OA causes more citations for better articles only (given that one uses overall citations as a rough measure of quality).
The data that Kristin illustrates do not show causation, only association. Articles available freely from repositories are associated with a higher frequency of citations. I have no contention with this claim, and everyone since Steve Lawrence (Nature, 2001) has backed this observation. What I am arguing, however, is that the likely (and primary) cause of the citation advantage is not increased access, but some quality differential, leading to better articles being deposited in the arXiv. In our manuscript, we argue that if OA-as-cause is present, its scope is severely limited to highly-cited articles. How can we say this?

If increased access was the cause of increased citations in our data, we should see a significant and positive correlation between fulltext article downloads from the arXiv and the number of citations an article receives. The rationale is that article repositories increases readership, some of which leads to increased citations (this is the argument that SPARC, Harnad, Suber and others use to justify the use of archives). Now please take a look at Figure 3 in our paper (http://arxiv.org/pdf/cs.DL/0603056). Notice that this positive association only applies to highly-cited articles (note: the inverse log of 2.5 is about 316 downloads).

In order to argue for causation one must be able to describe and measure the mechanism by which the cause takes place. Antelman (and others) demonstrate only the association between open access and citations, and infer that open access must be the cause. In our paper, we test the Open Access postulate, the Early View postulate, and a Quality Differential postulate. Of these three we feel that the Quality Differential is the strongest explanation for the data. We do not rule out Open Access completely, but the data do suggest that if access is responsible for increased citations, this effect may only take place for already highly-cited articles.

--Phil Davis