The latest work also delves into how papers become free to read.
To be certain, he says, one would need to check whether researchers citing the studies have access to paywalled content.
Priem says that one limitation of the study is that its samples included only articles with DOIs, which aren’t always used by publishers in the arts and humanities disciplines and in the developing world.
As tensions over the costs of institutional subscription packages grow between universities and publishers, the finding that roughly half of recently published research may be available to read for free could “tip the scales toward cancellation for some institutions”, the study says. “In the next few decades, we’re going to be seeing nearly all the literature available freely.” An earlier version of this story stated that free-to-read articles are cited 18% more than paywalled articles; in fact, the comparison is with the average for all articles for a given subject area and publication year.
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In this sample, 28% of articles were free-to-read, predicting a total of 19 million such articles in the literature.
Of papers published in 2015 — the most recent year examined — 45% were freely available, which suggests that newer articles are more likely to be open.
The study authors say theirs is the first broad analysis of the state of open research since a 2014 report produced for the European Commission.
But the two analyses employed different methods: the earlier one used automated software to search online for papers drawn at random from the Scopus database.
Around half the content being accessed was published in the past two years, says Priem.
The study, which hasn’t yet been peer-reviewed, is “careful and extensive”, says Ludo Waltman, deputy director of the Centre for Science and Technology Studies at Leiden University in the Netherlands who edits the Journal of Informetrics.