The "open access citation advantage" refers to the observed trend where research articles published in open-access journals or made openly accessible tend to receive more citations compared to articles behind paywalls or traditional subscription-based journals. This phenomenon has been documented in various studies across different academic disciplines.
As main conclusion, we found that funded research articles are generally more cited than unfunded ones, but the open access citation advantage in relation to the paywalled modality is higher for the unfunded articles. This open access citation advantage is strong both across fields and over time and come mainly from hybrid gold modality and the author self-archiving in open access repositories (green).
With regard to this study’s results, it supports the sustainability of the APC model; the OA articles have been keeping growing exponentially in quantity, with a higher citation performance leading to a citation advantage not only being sustained over time but also widening in some fields.
So, even though effects found here are more modest than reported elsewhere, given the conservative treatments of the data and when viewed in conjunction with other OACA studies already done [2,12], the results lend support to the existence of a real, measurable, open access citation advantage with a lower bound of approximately 20%;
Comparing the average relative citation impact of different access categories, the OACA is corroborated: Papers hidden behind a paywall were cited 10% below world average (ARC = 0.90), while those that are freely available obtain, on average, 18% more citations than what is expected (ARC = 1.18). However, citation impact differs between the different manners in which papers are made available for free: those that are only available as Green OA (ARC = 1.33) and Hybrid OA papers (ARC = 1.31) are cited the most with an impact of more than 30% above expectations, those available as Bronze are cited 22% above world average, while papers published as Gold OA obtain an ARC of 0.83. This constitutes an average relative citation impact of 17% below world average and 9% below that of articles hidden behind a paywall. Figure 5 below describes these findings.
While controlling for journal impact and publication date, we find that the OA status of an article increases the citation rate for that article by approximately one citation per year.
The results of this study show the positive impact of OA on the citation count. Likewise, the growth of OA articles in APC OA journals has been increasing exponentially. Moreover, it reflects that articles with online free access have more citations as compared to the articles without free online access, irrespective of the fact that those are published in the same OA journals.
On average, departments that published more OA content saw a greater citation advantage. The study results, and the literature reviewed, also indicated that some disciplines may have a greater citation advantage than other disciplines.
Results obtained from the present study establishes that in Library Science discipline, non-OA journals have greater citation impact, “citations per paper”; “citations per author”, “h-index”, “g-index”, “hI norm” and “hI annual” than OA journals. Out of 116 journals (58 non-OA and 58 OA) indexed in Scimago which published 23,528 and 19,773 papers, respectively, the citation percentage of non-OA journals (77.74%) was found to be greater than OA (22.26%) journals. The result obtained in the current study is completely different from the earlier studies (Antelman, 2004; Norris et al., 2008; Hajjem et al., 2005; Pourret et al., 2020) which were carried in other disciplines such as medicine, geochemistry, psychology, biology and ecology.
While we found only a single subject area (‘Art’) in which OA journal articles experienced a citation advantage on this measure, they found this for a larger number of subject areas (36 out of 249 for which ‘Art’ experienced the strongest advantage), but in the majority of subject areas (173) they find an OA citation disadvantage on this measure.
We found high risk of bias in nearly 98% of the included studies (Fig 2). High risk of bias/low validity in the population domain was often due to a poorly described sample or use of too narrow a sample to support the conclusions drawn. Few studies provided justification for their sample size.
Characteristics of research topics are believed to be determining in predicting their citation potentials. A good example may be observed in ‘hot’ topics, which are believed to easily acquire more citations and more papers than those dealt with in cold fields, as there are more papers focusing on similar topics [45]. Among other instances, to name, there are exciting and popular topics [46,47], controversial topics versus those contributing to scientific progress [83], fundamental versus super-specialised subjects with narrower audience [82] and finally positive and statistically significant versus negative outcomes [48]. Accordingly, it seems that important subject matters may acquire fewer citations, while popular, hot or trivial topics are more likely to gain more citations. Given the ‘self-selectivity postulate’, it would be probable that the OACA is a resultant of authors’ selectivity of topics with a high citation potential.
One such bias is the selection postulate, which suggests that authors may be more likely to make only their most impactful studies open access, leading to a skewed representation of the overall impact of open access articles. Additionally, there may be social or cultural biases that influence who cite OA articles and how frequently they are cited (Hanel et al., 2018). For instance, certain disciplines or geographical regions may be more likely to value or prioritize open access publishing.
The evidence here suggests that green OA, despite delays in access, enjoys a significant advantage in citation rates over gold OA, possibly due to enhanced discoverability. This result should play a role in the decision making of libraries, policy makers and other institutions as they consider the future of scholarly publishing.
The study's second aim shows that OA Citation Advantage applies to the type as well as the number of citations. OA articles consistently achieve a more diverse set of citations than non-OA articles. OA therefore enhances the interdisciplinarity of work.
By analysing large-scale bibliographic data from 2010 to 2019, we found a robust association between open access and increased diversity of citation sources by institutions, countries, subregions, regions, and fields of research, across outputs with both high and medium–low citation counts. Open access through disciplinary or institutional repositories showed a stronger effect than open access via publisher platforms.
In conclusion, our empirical study suggests that articles published as hybrid Gold open access on the journal site are associated with higher citation rates than subscription, self-archived, or otherwise openly accessible articles. Hybrid Gold open access articles are more likely to be cited by peers than subscription articles published in the same journal in the ‘Clinical Medicine’ discipline. Further studies are required to examine any hybrid Gold open access citation advantage trends across other areas and disciplines, as well as other data sources.
Though the publish-or-perish model still reigns in academia, there is great potential in encouraging tenured professors to publish OA by supplementing the costs through institutional grants and other incentives wrapped into a tenure agreement. Perhaps through this model, as Gargouri et al. have suggested, the longstanding publish-or-perish doctrine will give way to an era of "self-archive to flourish." (32)
First, the data reveal evidence that shows the highest important relation to citation advantage is advance publication of accepted articles.
As shown in Fig. 5, for all the groups, the average number of twitter and facebook of OA articles is 2.8–3.4, which is slightly more than the number of non-OA articles, when the ratio of OA articles to non-OA articles is 1.27–1.48. OA articles attract a litter more social media attention than non-OA articles.
This study finds that OA links tend to generate more article visits than paid content links on social media platforms. On average, OA links receive twice as many clicks as paid content links. In particular, when the post does not indicate that a linked article is OA, there is an obvious drop in performance against the clicks on links indicating the OA status. As confirmed in many previous studies, OA articles attract more downloads, social media attention, and citations than non-OA articles; we find that the OA effect also applies for links to scholarly articles. OA links receive more clicks than paid content links, which means the articles attract more readers.
Our study demonstrates a significant positive correlation between article Twitter mention and citation score. It provides further evidence that social media engagement can be beneficial to the dissemination of academic information. It also suggests that the open-access status of an article may increase Twitter mentions and help increase an article’s social media engagement.
About the reasons why there is no OA advantage or even OA disadvantage at journal level, we believe that is the personal motivation of each author individually that leads him/her to try to improve the visibility and access of its works. For this purpose, it uses the green access as well as comments on blogs and social networks. For these authors, there is an advantage of citation at the paper level. However, by adding the impact of many authors in a journal, the fact that it is an open access journal makes the responsibility for dissemination diluted between the publisher and the group of authors, causing some of them to consider that the task of dissemination must rest exclusively on the journal. In this way, subscription journals benefit from its subscriber network and at the same time from the effort of many of its authors to facilitate access through the greenway.
Our results show that contrary to this belief, paying high costs does not necessarily increase impact of publications. First, large publishers with high impact are not the most expensive in terms of APCs. Second, publishers with highest APCs are not necessarily the bests in terms of impact. Correlation between APCs and impact is moderate.
There is a high degree of variability in uncitedness for the case of journals, but in half of the 316 disciplines considered in the present study the average uncited rate is higher than 47% at two years after publication. The disciplines with the highest uncited rates correspond to Humanities, while the lowest uncitedness is observed in Life Sciences (especially in Chemistry and Materials) and Health Sciences. As for access modality, the uncited rates in the group of OA journals are generally higher than those in the group of paywalled ones, at least when it is not distinguished by journal visibility. Specifically, in 65% of disciplines the uncited rate is higher within the OA journals, while in 29% of cases uncitedness is higher in the paywalled ones.
With respect to the correlation between uncitedness and the so-called “OA citation advantage”, some considerations can be made. We do not find any strong correlation between OA and uncitedness. This is important because it provides new evidence in the debate about OA citation advantage. Within the group of most cited journals (Q1 and top 10%), OA journals generally have somewhat lower uncited rates. This could be due to the OA citation advantage effect. Papers published in the most widely distributed journals receive more citations when they are published openly. This OA citation advantage effect would also reduce the uncited rate in this group of top journals. This is because a part of the papers that would not receive any citation within a paywalled journal could now receive some citations when they are distributed in OA.
Something similar is observed within the journals with lowest visibility. In the last quartile (Q4), uncitedness is again somewhat lower in the case of the OA journals. This group corresponds to those journals for which many institutions do not have a subscription, and therefore OA facilitates visibility and impact. Unfortunately, institutions that cannot maintain full subscriptions to publishers first drop the subscription to this group of least read and cited journals.
However, in the intermediate quartiles (Q2 and Q3) no differences are observed between access modalities in relation to the uncited rate. Within the group of journals in intermediate positions in the rankings by impact factor, there is no observed OA citation advantage, at least in relation to a possible reduction of the uncited rate. This seems to indicate that access modality is not a determining factor for reading a paper, at least in the group of journals with a medium perceived quality.
In general, the citation advantages measured with the H-index, JIF and CPP were very similar in APC and non-APC OAJs. Quartile rank, however, indicated that APC journals tended to have a higher impact than non-APC journals. This pattern was reversed in our subclass analysis, which found no significant difference between APC and non-APC journals in terms of quartile rank, whereas citation impact measured with the H-index, JIF and CPP was significantly greater in non-APC journals. Our subclass comparisons showed a statistically significant difference between APC and non-APC OAJs at the field level. In other words, for APC OAJs we found no difference in citation impact among subclasses considering three metrics (JIF, H-index and CPP), but did find differences for non-APC OAJs.
The results show that Sci-hub indexes the majority of scientific publications as the share of non-OA publications available in Sci-hub increased from 55 to 76% between 2009 and 2019. This progression negatively affects the OACA. Thus, publications in fully OA journals receive on average more citations than their equivalents accessible by subscription (non-OA), on the condition that the latter are not available in Sci-hub. We observed the same trend for publications in hybrid journals; OA publications in these journals receive on average more citations than non-OA ones. As for publications in OA journals, in hybrid journals the OACA is less if subscription-based articles are available in Sci-hub. Therefore, this study showed for the first time, on a large-scale randomized analysis, that the OACA does exist, and that the development of the dark route of open access tends to reduce it.