With Plan S coming into effect earlier this year, there has been much discussion regarding the potential benefits and challenges associated with open access. It has been suggested that open access articles are available to a larger audience than those published behind paywalls, leading to increased visibility, readership and impact. Citations are often used to measure these factors. However, a number of studies have failed to reach a consensus on whether an open access citation advantage exists.

Dr Isabel Basson and colleagues aimed to address this question by applying three measures of citation advantage:

• normalised citation score (NCS) – indicates if an article received the expected number of citations and corrects for subject area and publication year
• citedness – whether articles were cited by individuals other than the authors within 2 years of publication
• most frequently cited – the percentage of publications in the most frequently cited 1%, 5% and 10% of articles in each subject area.

The study, published in Scientometrics, used open access labels in the Web of Science (WoS) metadata to identify open access articles published in journals listed in the Directory of Open Access Journals and compared measures of citation advantage with subscription journal articles. Limiting the articles to English-language only to avoid a potentially confounding effect of language, the authors identified over 3.6 million articles of which 87.3% were published in subscription journals and 12.7% were published open access. The proportion of open access versus subscription journal articles varied considerably with individual subject areas.

Basson and colleagues reported results for the three measures of citation advantage:

• NCS –a relationship between NCS and access status was found in 76 (30%) of the 250 WoS subject areas investigated. An open access citation advantage was only seen in one subject area; in the remaining 75 subject areas subscription journal articles showed a citation advantage.
• Citedness – a relationship between citedness and access status was seen in fewer than half of subject areas, only 4 of which showed an open access citation advantage.
• Most frequent cited – the citation advantage favoured subscription journal articles rather than open access journal articles in the majority of subject areas.

Across all measures of citation advantage, only six of the 250 subject areas in WoS were reported to experience an open access citation advantage compared with subscription journal articles.

This study was one of the first to use open access labels in the WoS metadata to investigate citation advantage with access status. Overall, the authors conclude that access status accounts for little of the variability in the number of citations an article receives and suggest that other factors need to be considered when explaining variation in citation.

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