Uptake of OA

From 2010 to 2014, 909 journals published at least one paper indexed as GHR. Figure 1 provides an overview of the frequency of different access categories at the journal (Fig. 1a) and paper level (Fig. 1b). Including both those with and without APCs, 18.8% journals and 18.6% papers are available through gold OA. While there are less gold OA journals with an APC, the percentage of papers published in these periodicals (12.0%) exceeds those in gold OA journals without an APC (8.6%), most likely because they are more renowned and have impact factors (IFs) (such as Lancet Global Health, PLOS Medicine and Global Health Action). The majority of journals (64.2%) are hybrid, meaning that authors can choose to publish research in closed access without financial cost or provide an APC and make the paper OA; still, only 6.8% of papers make use of the hybrid OA option. If immediate OA access is sought via the publisher, GHR researchers seem to choose gold journals over hybrid ones. On the paper level, 69.2% of all GHR publications are not available for free on the publishers’ website. However, 27.2% of toll accessed papers are self-archived (also called green OA) leaving a total of 42.0% of GHR papers only accessible through subscription or toll access.

Fig. 1 Percentage of journals (a) and articles (b) per type of access category Full size image

According to the archiving policy recorded by RoMEO, 84.0% of the 700 subscription and hybrid journals allow green OA, while 7.4% explicitly prohibit it (8.9% of the 700 subscription and hybrid journals were not graded by RoMEO). Among RoMEO-graded subscription and hybrid journals, we determined that 733 papers were self-archived in accordance to journal policy and 1139 were not self-archived, despite authors having the possibility of doing so according to the journal policy. This shows that 60.8% of papers that could have been self-archived were not. In a field where OA seems of practical and ethical importance for the sharing of knowledge promoting health equity, it is surprising that researchers do not make their papers available when they are legally able to do so without any cost; this suggest that authors might not be aware of green OA policies.

Cost of OA

Figure 2 presents the total APCs required for GHR publications over the 2010–2014 period, by publisher and OA category. The total fees amounted to US$1.7 million for 627 gold OA (APC) and hybrid papers; on average, authors paid US$2732 (SD = US$1090) to make their publication freely available on the publisher’s website. These APCs can be explained by many factors, such as the high scholarly capital associated with publishing in journals of big publishers (which are generally hybrid), as well as the presence of an oligopoly in the academic publishing system [40]. Such oligopolistic conditions create a limited market, reducing economic competition between publication houses and giving little incentive to decrease prices. More specifically, according to our findings, 93.4% of APCs were paid to journals owned by the 10 most prominent publishing companies. Elsevier alone accounts for 22.8% of the total APCs and charged the highest average gold APCs (on average US$4435 for 69 papers) among all publishers in the GHR set. Their APCs for 26 hybrid fees were lower and close to the GHR average at US$3271 per paper; nevertheless, Elsevier’s hybrid uptake remained low at 3.5%.

Fig. 2 Sum of gold and hybrid article processing charges per publisher Full size image

Mean OA fees in hybrid journals (US$3240 per paper) are higher than those in gold OA journals (US$2452), which is somewhat surprising given that the former group of journals already has revenues from subscriptions [43], while APCs are the main source of revenues of the latter. Historically, hybrid journals have justified this double income stream as a way to reduce subscription fees proportionally with the uptake of OA [44]. However, this fee reduction has been questioned given the lack of transparency of journal costs and the growing fees of both APCs and subscriptions [45]. This lack of transparency augments the possibility of a phenomenon of ‘double dipping’, in which journals profit from both revenue streams – APCs and subscriptions – without readjusting the price based on APC uptake [46]. Even though APCs are getting considerably expensive, they continue to be promoted by many important stakeholders and funders making gold and hybrid OA publishing a growing business [47].

Impact of OA

Figure 3 demonstrates the number of papers and the mean number of citations per type of OA. Articles categorised as delayed, green and hybrid OA are cited above average while toll access and gold OA papers are cited below average. Of particular interest is the difference between green OA (1.5) and toll access (0.7), which shows that self-archived papers receive more than twice as many citations as those hidden behind a paywall, which corroborates previous findings obtained in other fields [48, 49]. It should be noted that the green OA articles available on PubMed Central were cited more (1.9) than those deposited on other platforms (1.3).

Fig. 3 Citation impact and number of papers per access category Full size image

Hybrid articles were cited 37% more than the average GHR paper and twice as much as toll access articles, which supports the previous findings that OA broadens citation impact. However, one has to keep in mind the paramount fees for hybrid publishing, while self-archiving comes at no charge to the author and a higher increase in impact. Although proper IT infrastructure and human resources are necessary to ensure an organised, indexed and sustainable repository, studies show that such costs are meager compared to subscription or gold and hybrid OA (e.g. [35, 50]). Articles published in gold OA journals remained cited 40% below the average GHR paper, with no difference between APC and non-APC journals. The fact that the impact of gold OA papers is lower than those published in subscription journals (green, hybrid, toll) can be partly explained by the fact that prestigious journals are largely subscription journals, while many gold OA journals are younger and, thus, are not as prestigious. Journal prestige is an important confounding factor that limits this type of study [51]. Results for delayed OA and other papers are based on as few as 49 and 16 papers, respectively. Given this limited number, results are inconclusive.

Usage of GHR papers varied according to the socioeconomic situation of countries (Fig. 4). Indeed, 3.1% of the 42,479 citing WBA category-cited paper combinations came from low-income countries, 8.5% from lower middle-income, 20.0% from upper middle-income and 68.4% from HICs. Such underrepresentation of researchers from LMICs is well-known [52, 53]. Analysing the average share of citing countries per paper, researchers from low-income countries were, on average, 29.0% and 46.9% more likely to cite papers from gold OA journals with and without an APC and 8.6% more likely to cite a green OA paper, while they were underrepresented on papers citing hybrid (–37.4%) and toll access papers (–15.0%). The underrepresentation of LMICs on papers citing hybrid papers show that, even with availability on the publisher’s website, such articles are rarely considered by LMIC researchers. This may simply be the result of subscription journals not traditionally being accessible and thus researchers are not in the habit of searching in such resources. The results for HICs suggest that the type of access has less influence on HIC authors. However, they are underrepresented on papers citing articles published in gold OA journals with (–16.8) and without (–5.8) APCs, which might again be explained by the lower prestige of these journals in comparison to many traditional subscription-based journals.

Fig. 4 Over- and underrepresentation of citing countries by World Bank Atlas (WBA) country classification (a, low-income countries; b, lower middle-income; c, upper middle-income; d, high-income countries) and access category. Numbers in parentheses represent the number of papers cited by each country category as well as the number of citing WBA category-cited paper combination Full size image

Limitations

The first limitation of this study pertains to the calculation of green OA articles at the paper level. After we compiled the number of PubMed articles that were freely available in green OA format, we performed a manual search on Google to assess other articles that may be freely accessible. We used the author’s name and the title of the article, and then looked at the top ten results to find a green OA article. We found many articles on institutional repositories, publicly based repositories and social media sites. However, there may be some available research that was simply not found by our search method.

The second limitation is regarding the calculation of costs (APCs) paid by authors. In cost calculations, we did not include waivers or institutional discounts. Waivers can be given to cover part or all of APCs where funding is limited, especially in the case where a researcher is affiliated to an institution in a LMIC. Waivers are generally granted on a case by case basis and are not made public. Institutional discounts were also not included in our calculation because they are quite variable based on institution and year. In our study, APC costs were gathered in 2016, but APCs were paid before that time and thus may have been different – most likely slightly lower due to inflation. Given all these factors, the total APCs may be slightly overestimated herein.

The third limitation pertains to the categorisation of citing papers written by authors from different countries once per WBA country group. This decision was made because it is not possible to know how much contribution each author made to the paper. We could (1) fractionalise by number of authors or country group according to WBA classification or (2) count once for each author or country group. Since we analyse on the country level (or country group according to WBA) we do not wish to risk punishing papers with multiple authors that are in more than one country groups.

The fourth limitation is that we decided to compare average citation rate of different access levels without controlling for IF. We decided not to include the IF as it is a flawed indicator already overused in the scientific community [54]. It is also discipline-specific and not readily comparable between fields. Additionally, in this specific study, the majority of the 909 journals published only one or a few papers; such an analysis would be performed on very small amounts of data. However, herein, we did make the logical assumption that closed journals will most likely have more prestige because prestige is built with time, something that is not yet acquired with novel OA journals. Yet, there is no empirical evidence-based research to validate this last assumption.