Hajjem, Chawki and Harnad, Stevan
The Self-Archiving Impact Advantage: Quality Advantage or Quality Bias?
In astrophysics, Kurtz found that articles that were self-archived by their authors in Arxiv were downloaded and cited twice as much as those that were not. He traced this enhanced citation impact to two factors: (1) Early Access (EA): The self-archived preprint was accessible earlier than the publisher's version (which is accessible to all research-active astrophysicists as soon as it is published, thanks to Kurtz's ADS system). (Hajjem, however, found that in other fields, which self-archive only published postprints and do have accessibility/affordability problems with the publisher's version, self-archived articles still have enhanced citation impact.) Kurtz's second factor was: (2) Quality Bias (QB), a selective tendency for higher quality articles to be preferentially self-archived by their authors, as inferred from the fact that the proportion of self-archived articles turns out to be higher among the more highly cited articles. (The very same finding is of course equally interpretable as (3) Quality Advantage (QA), a tendency for higher quality articles to benefit more than lower quality articles from being self-archived.) In condensed-matter physics, Moed has confirmed that the impact advantage occurs early (within 1-3 years of publication). After article-age is adjusted to reflect the date of deposit rather than the date of publication, the enhanced impact of self-archived articles is again interpretable as QB, with articles by more highly cited authors (based only on their non-archived articles) tending to be self-archived more. (But since the citation counts for authors and for their articles are correlated, one would expect much the same outcome from QA too.) The only way to test QA vs. QB is to compare the impact of self-selected self-archiving with mandated self-archiving (and no self-archiving). (The outcome is likely to be that both QA and QB contribute, along with EA, to the impact advantage.)
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