Prevalence of Open Access publishing
V.A Traag 
Description
Open Access publishing is one of the pillars of Open Science. Whereas traditional academic publishing charges a fee for reading a publication, Open Access publications are free to read, not only by scientists, but also by the general public. In addition to being free to read, most definitions of Open Access also require publications to be reusable (Suber 2012).
There are various models of Open Access publishing. Hybrid Open Access journals publish both Toll Access, where readers have to pay a fee, and Open Access articles. Some journals publish all articles Open Access, this is called Gold Open Access. If no fee is charged for publishing in such an only Open Access journal, this is called Diamond Open Access. If a publication in a journal is also deposited in a publication repository, for instance a university repository, and is made available openly, this is called Green Open Access. Finally, some articles are freely available from the website of the publisher, but have no licence attached to them, so it is not clear whether the article will remain freely available in the future and under what conditions it can be used. This is sometimes called Bronze Open Access. For an overview of the typology see (Robinson-Garcia, Costas, and Leeuwen 2020).
In summary, we have the following types of Open Access:
- Green
- Article that is deposited in an Open Access repository.
- Gold
- Open Access article in a journal that publishes only Open Access articles.
- Diamond
- Open Access article in a journal that publishes only Open Access articles.
- No publishing fee, i.e. no APC
- Hybrid
- Open Access article in a journal that also publishes Closed Access articles.
- Typically charges an APC
- Bronze
- Article that is accessible without paywall from a publisher.
- No licence attached, unclear whether article will remain freely available in the future and under what conditions it can be used.
Note that the different Open Access statuses are not necessarily mutually exclusive. In particular, any article can be both Green Open Access and any other type of Open Access. Similarly, Diamond Open Access is a subtype of Gold Open Access, so that every Diamond Open Access article is also Gold Open Access.
We are here interested in the extent to which articles are published Open Access. Tracking such an indicator over time could provide some idea of whether how the uptake of Open Access publishing develops. We can split out the overall uptake of Open Access publishing per type of Open Access to understand the developments in more detail.
Books and other material can also be published Open Access, but Open Access publishing has not yet been taken up frequently in book publishing (Grimme et al., n.d.). The book publishing landscape is also quite scattered and challenging. Books, especially monographs, play an important role in various fields in the humanities and social sciences. Also including books in studies of Open Science is therefore particularly relevant for these fields. However, we do not (yet) include a metric for Open Access books here.
There are some recurrent questions around Open Access publishing. Some questions concern effects of Open Access publications, for instance whether Open Access increases the impact of publications. Other questions focus on effect on Open Access, for instance whether certain Open Access mandates increasing Open Access publishing. By measuring the overall uptake of Open Access publishing, this indicator can help answer such questions.
Metrics
Number/% of Open Access journal publications (per OA type)
By counting he overall number of Open Access publications, we get a first impression of the overall uptake of Open Access publishing. If Open Access publishing becomes more widespread, we expect to see more Open Access publications, and hence, by counting the number of Open Access publications, we may get some idea of the overall uptake of Open Access publishing.
This metric is expected to scale with the overall number of publications, and we therefore call it a size-dependent metric.
One limitation of simply counting the number of Open Access publications is that it may partly reflect the general trends of publishing. For instance, suppose we observe an increase in the number of Open Access publications. We could then conclude that Open Access publishing has become more widespread. In terms of the sheer amount of scientific knowledge that has become openly available, this is observation seems to be quite right. However, suppose that the increase in Open Access publications is simply proportional to the overall increase in total number of publications. This may then indicate that overall, the chance of a paper being published Open Access has remained the same. This may indicate that, for instance, researchers have not become more likely to publish Open Access. What viewpoint is more relevant depends on the context. For this reason, we therefore also describe a metric of the % of Open Access publications.
We can count the number of Open Access publications based on different selections. For instance, we may want to select only publications within a particular country, institution, field of science or publication year. We do not describe here how to make such selections, we here merely clarify how to count the Open Access publications, given a particular set of publications. As explained in the Description, we can distinguish between different types of Open Access publications: Hybrid, Gold, Diamond, Green and Bronze. We will clarify how to measure these aspects of Open Access publishing.
Measurement
For each publication we need to measure whether it is Open Access at all, and if so, what specific type(s) of Open Access it is. In order to be able to do this, we need to know whether the publication is deposited in one or more publication repositories (for Green OA) and know whether the article is directly available from the publisher. In the latter case, we also need to be able to know whether the journal itself is fully Open Access or whether it is a hybrid journal. In addition, if it is a fully Open Access journal, we need to determine whether the journal charges any publishing fees (APC), if it does not, we can classify it additionally as Diamond Open Access.
Hence, this requires (1) data on publication repositories; (2) data on published articles; and (3) data on journals. Fortunately, much, but not all, of this information is integrally available from some existing datasources.
By looking at the percentage of Open Access publications, we get an idea of the uptake of Open Access publishing as a practice. That is, it provides an indicator of the likelihood that a publication is published Open Access. If this percentage increases, it suggests that scholars are more often publishing their work Open Access. Unlike the Number of Open Access publications, this metric does not scale with the overall number of publications, and is therefore called a size-independent metric.
We can study the percentage of Open Access publications based on different selections. For instance, we may want to select only publications within a particular country, institution, field of science or publication year. We do not describe here how to make such selections, we here merely clarify how to calculate the percentage of Open Access publications, given a particular set of publications.
Datasources
Unpaywall
Unpaywall is a database that contains information about online locations of scholarly publications and the Open Access status of these locations (Piwowar et al. 2018). Unpaywall is organised on the basis of DOIs and is limited to Crossref DOIs. For each DOI, information about online locations and Open Access status is provided based on scraping journal websites and publication repositories. Sometimes, information from Unpaywall may be incorrect (Piwowar et al. 2018), so there is room for improvement.
There are some particular limitations regarding Green Open Access. First, Unpaywall may not be able to track all publication repositories. Hence, it might be that some publications are in reality Green Open Access, but Unpaywall may have missed the repository from which it is available. Second, even if Unpaywall has located a repository from which the publication is available, it is difficult to ascertain whether it is the same version as the published version, or whether there are still some differences.
Unfortunately, Unpaywall does not record whether a journal charges an APC or not, and so we cannot determine whether an article is Diamond Open Access. Please see the indicator on Journal Open Access journals.
Unpaywall can easily be used through an API, as illustrated below.
import requests
doi = '10.7717/peerj.4375'
email = 'unpaywall_01@example.com'
url = f'https://api.unpaywall.org/v2/{doi}?email={email}'
response = requests.get(url)
doi_info = response.json()Please note that the online API is rate-limited, and for bulk access, it is highly preferable to download the complete dataset and process it locally. Unpaywall provides a field is_oa, which indicates whether the article is Open Access. In addition, it provides the field oa_status, which clarifies the type of Open Access (limited to gold, hybrid, bronze, green and closed). However, this assigns a publication to only one Open Access type, while an Open Access publication can in principle be both Green Open Access and any other type of Open Access.
Instead of using the Unpaywall provided Open Access status, we can also define Open Access status explicitly. This in particular allows us to define multiple Open Access statuses for a single paper. We can do that as illustrated below.
oa_green = False
oa_gold = False
oa_hybrid = False
oa_bronze = False
for location in doi_info['oa_locations']:
if location['host_type'] == 'repository':
oa_green = True
elif location['host_type'] == 'publisher':
if doi_info['journal_is_oa']:
oa_gold = True
else:
if location['licence']:
oa_hybrid = True
else:
oa_bronze = TrueTo facilitate interaction with the Unpaywall API there are also supporting packages available in Python (https://pypi.org/project/unpywall/) and R (https://cran.r-project.org/package=roadoi).
Once we know the Open Access status of each publication, we can easily calculate the percentage, simply as the number of publications out of the total that are Open Access. Additionally, we can do this for each separate Open Access type. We could for example refer to the % Green OA or % Gold OA. Note that percentages may not add up to 100%, but the total may also even exceed 100%, because publications can have both a Green Open Access status and another Open Access status. For that reason, you should not report percentages of Open Access statuses in a cumulative fashion (e.g. not in a stacked bar chart), in particular not when reporting on Green Open Access.
Known correlates
There is a large ongoing debate whether Open Access publishing increases the citation impact of publications, known as the so-called Open Access citation advantage. A recent systematic review on the topic suggests that the evidence is inconclusive (Langham-Putrow, Bakker, and Riegelman 2021).
References
Reuse
Citation
@online{apartis2024,
author = {Apartis, S. and Catalano, G. and Consiglio, G. and Costas,
R. and Delugas, E. and Dulong de Rosnay, M. and Grypari, I. and
Karasz, I. and Klebel, Thomas and Kormann, E. and Manola, N. and
Papageorgiou, H. and Seminaroti, E. and Stavropoulos, P. and Stoy,
L. and Traag, V.A. and van Leeuwen, T. and Venturini, T. and
Vignetti, S. and Waltman, L. and Willemse, T.},
title = {Open {Science} {Impact} {Indicator} {Handbook}},
date = {2024},
url = {https://handbook.pathos-project.eu/sections/1_open_science/prevalence_open_access_publishing.html},
doi = {10.5281/zenodo.14538442},
langid = {en}
}