Looking into Pandora's Box: The Content of Sci-Hub and its Usage

Despite the growth of Open Access, potentially illegally circumventing paywalls to access scholarly publications is becoming a more mainstream phenomenon. The web service Sci-Hub is amongst the biggest facilitators of this, offering free access to around 62 million publications. So far it is not well studied how and why its users are accessing publications through Sci-Hub. By utilizing the recently released corpus of Sci-Hub and comparing it to the data of ~28 million downloads done through the service, this study tries to address some of these questions. The comparative analysis shows that both the usage and complete corpus is largely made up of recently published articles, with users disproportionately favoring newer articles and 35% of downloaded articles being published after 2013. These results hint that embargo periods before publications become Open Access are frequently circumnavigated using Guerilla Open Access approaches like Sci-Hub. On a journal level, the downloads show a bias towards some scholarly disciplines, especially Chemistry, suggesting increased barriers to access for these. Comparing the use and corpus on a publisher level, it becomes clear that only 11% of publishers are highly requested in comparison to the baseline frequency, while 45% of all publishers are significantly less accessed than expected. Despite this, the oligopoly of publishers is even more remarkable on the level of content consumption, with 80% of all downloads being published through only 9 publishers. All of this suggests that Sci-Hub is used by different populations and for a number of different reasons, and that there is still a lack of access to the published scientific record. A further analysis of these openly available data resources will undoubtedly be valuable for the investigation of academic publishing.


Introduction
Through the course of the 20th century, the academic publishing market has radically transformed. What used to be a small, decentralized marketplace, occupied by university presses and educational publishers, is now a global, highly profitable enterprise, dominated by commercial publishers 1 . This development is seen as the outcome of a multifactorial process, with the inability of libraries to resist price increases, the passivity of researchers who are not directly bearing the costs and the merging of publishing companies, leading to an oligopoly 2 .
In response to these developments and rising subscription costs, the Open Access movement started out to reclaim the process of academic publishing 3 . Besides the academic and economic impact, the potential societal impact of Open Access publishing is getting more attention 4,5 , and large funding bodies seem to agree with this opinion, as more and more are adopting Open Access policies 6-8 . These efforts seem to have an impact, as a 2014 study of scholarly publishing in the English language found that, while the adoption of Open Access varies between scholarly disciplines, an average of around 24 % of scholarly documents are freely accessible on the web 9 .
Another response to these shifts in the academic publishing world is what has been termed Guerilla Open Access 1 , Bibliogifts 10 or Black Open Access 11 . Or in short, the usage of semi-legal or outright illegal ways of accessing scholarly publications, like peer2peer file sharing, for example the use of #icanhazpdf on Twitter 10 , or centralized web services like Sci-Hub/LibGen 12 .
Especially Sci-Hub, which started in 2011, has moved into the spotlight in the recent years. According to founder Alexandra Elbakyan, the website uses donated library credentials of contributors to circumvent publishers' paywalls and thus downloads large parts of their collections 13 . This clear violation of copyright not only lead to a lawsuit by Elsevier against Elbakyan 14 , but also to her being called "the Robin Hood of Science" 15 , with both sparking further interest in Sci-Hub.
Despite this, there has been little research into how Sci-Hub is used and what kind of materials are being accessed through it. A 2014 study has looked at content provided through LibGen 10 . In 2016 Sci-Hub released data on ~28 million downloads done through the service 16 . This data was subsequently analyzed to see in which countries the website is being used, which publishers are most frequent 13 and how downloading publications through Sci-Hub relates to socio-economic factors, such as being based in a research institution 17 and how it impacts interlibrary loans 12 .
In March 2017 Sci-Hub released the list of ~ 62 million Digital Object Identifiers (DOIs) of the content they have stored. This study is the first to utilize both the data on which publications are downloaded through Sci-Hub, as well as the complete corpus available through them. This allows a data-driven approach to evaluate what is stored in the Sci-Hub universe, how the actual use of the service differs from that, and what different use cases people might have for Sci-Hub.

Data sources
The data on the around 62 million DOIs indexed by Sci-Hub was taken from the dataset released on 2017-03-19 18 . In addition, the data on the 28 million downloads done through Sci-Hub between September 2015 and February 2016 16 was matched to the complete corpus of DOIs. This made it possible to quantify how often each object listed in Sci-Hub was actually requested from its user base.

Resolving DOIs
The corresponding information for the publisher, the year of publication, as well as the journal in which it was published was gotten from doi.org, using the RubyGem Terrier (v1.0.2, https:// github.com/Authorea/terrier). Acquiring the metadata for each of the 62 million DOIs in Sci-Hub was done between 2017-03-20 and 2017-03-31. In order to save time, the DOIs of the 28 million downloads were then matched to the superset of the already resolved DOI of the complete Sci-Hub catalog. In both cases, DOIs that could not be resolved were excluded from further analysis, but they are included in the dataset released with this article.

Tests for over-& under-representation
For each publisher, the number of papers downloaded was compared to the expected number of downloads, given the publishers' presence in the whole Sci-Hub database. For this the relative contribution to the database was calculated for each publisher, excluding all missing data. The number of actual downloads was then compared to the expected number of downloads using a binomial test. All p-values were corrected for multiple testing with False Discovery Rate 19 and post-correction p<0.05 were accepted.

Resolving the Sci-Hub DOIs
For the 61,940,926 DOIs listed in the Sci-Hub data dump, a total of 46,931,934 DOIs could be resolved (75.77%). Manual inspection of the unresolvable 25% shows that nearly all of these could not be resolved as they are not available via doi.org, and are not a technical error in the procedure to resolve them (i.e. lack of internet connection). For the data on the downloads done through 21,515,195 downloads could be resolved out of 27,819,965 total downloads (77.34%).

The age of publications in Sci-Hub
To estimate the age distribution of the publications listed in Sci-Hub, and which fraction of these publications is actually requested by the people using Sci-Hub, the respective datasets were tabulated according to the year of publication, see Figure 1. While over 95% of the publications listed in Sci-Hub were published after 1950, there is nevertheless a long tail, reaching back to the 1619 edition of Descriptio cometae 20 .
As a general trend the number of publications listed in Sci-Hub increases from year to year. Two notable exceptions are the time periods of the two World Wars, at which ends the number of publications dropped to pre-1906 and pre-1926 levels, respectively (red bars in Figure 1).
When it comes to the publications downloaded by Sci-Hub users, the skew towards recent publications is even more extreme. Over 95% of all downloads fall into publications done after 1982, with ~35% of the downloaded publications being less than 2 years old at the time they are being accessed (i.e. published after 2013). Despite this, there is also a long tail of publications being accessed, with articles published even in the 1600s being amongst the downloads, and 0.04% of all downloads being made for publications released prior to 1900.

Which journals are being read?
The complete released database contains ~177,000 journals, with ~60% of these having at least a single paper downloaded. The number of articles per journal likely follows an exponential function, for both the total number of publications listed on Sci-Hub as well as the number of downloaded articles (see Supplementary Figure S1), with <10% of the journals being responsible for >50% of the total content in Sci-Hub. The skew for the downloaded content is even more extreme, with <1% of all journals getting over 50% of all downloads.
Contrasting the 20 most frequent journals in the complete database with the 20 most downloaded ones (Figure 2), one observes a clear shift not only in the distribution but also in the ranking, with the most abundant journal of the whole corpus not appearing in the 20 most downloaded journals. In addition, chemical journals appear to be overrepresented in the downloads (12 journals), compared to the complete corpus (7 journals), with no other discipline showing an increase amongst the 20 most frequent journals.

Are publishers created equal?
Looking at the data on a publisher level, there are ~1,700 different publishers, with ~1,000 having at least a single paper downloaded. Both corpus and downloaded publications are heavily skewed towards a set of few publishers, with the 9 most abundant publishers having published ~70% of the complete corpus and ~80% of all downloads respectively (see Supplementary Figure S2).
Given the background frequency in the complete corpus, the download numbers were compared to the expected numbers using a binomial test. After false discovery rate correction for multiple testing, 982 publishers differed significantly from the expected download numbers, with 201 publishers having more downloads than expected and 781 being underrepresented. Interestingly, while some big publishers like Elsevier and Springer Nature come in amongst the overly downloaded publishers, many of the large publishers, like Wiley-Blackwell and the Institute of Electrical and Electronics Engineers (IEEE) are being downloaded less than expected given their portfolio ( Figure 3).

Discussion
Earlier investigations into the data provided through Sci-Hub and LibGen focused large on either on the material being accessed 13 or on the data stored in these resources 10 . This study is the first to make use of both the whole corpus of Sci-Hub as well as data on how this corpus is being accessed by its users.
Why Sci-Hub? Comparing actual usage with the background set of articles shows that articles from recent history are highly sought for, giving some evidence that embargoes prior to making publications Open Access seem to become less effective. These findings are in line with prior research into the motivations for crowd-sourced, peer2peer academic file sharing 21 . While embargoes have impact on the use of those publications 22 , these hurdles are being surpassed more and more by Black Open Access 11 , as provided by Sci-Hub.
While a good part of the literature available through Sci-Hub seems to be rarely accessed, the long tail of, publications, especially older ones, seems to be put to use -albeit at a lower frequency. With DOIs that are unresolvable due to issues on publishers' sides 23 , and with Open Access publications that disappear behind accidental Who's reading?
Looking at the disproportionately frequented journals, one finds that 12 of the 20 most downloaded journals can broadly be classified as being within the subject area of chemistry. This is an effect that has also been seen in a prior study looking at the downloads done from Sci-Hub in the United States 12 . In addition, publishers with a focus on chemistry and engineering are also amongst the most highly accessed and overrepresented. While it is unclear whether this imbalance comes due to lack of access by university libraries, it's noteworthy that both disciplines have a traditionally high number of graduates who go into industry. The 2013 Survey of Doctorate Recipients of the National Center for Science and Engineering Statistics (NCSES) of the United States finds that 50% of chemistry graduates and 58% of engineering graduates move to private, for-profit industry while only 32% and 27% respectively stay at educational institutions 25 . In comparison, in the life sciences these numbers are nearly switched, with 52% of graduates staying at educational institutions, which presumably offer more access to the scientific literature.

Non solus. Or at least not completely
The prior analysis of the roughly 28 million downloads done through Sci-Hub showed a bleak picture when it came to the diversity of actors in the academic publishing space, with around 1/3 of all articles downloaded being published through Elsevier 13 . The analysis presented here puts this into perspective with the whole space of academic publishing available through Sci-Hub, in which Elsevier is also the dominant force with ~24% of the whole corpus. The general picture of a few publishers dominating the market, with around 50% of all publications being published through only 3 companies, is even more pronounced at the usage level compared to the complete corpus, perpetuating the trend of the rich getting richer. Only 11% of all publishers, amongst them already dominating companies, are downloaded more often than expected, while publications of 45% of all publishers are significantly less downloaded.

Supplementary materials
Supplementary Figure  Click here to access the data

Conclusions
The analyses presented here suggest that Sci-Hub is used for a variety of reasons, by different populations. While most usage is biased towards getting access to recent publications, there is a subset of users interested in getting historical academic literature. Compared to the complete corpus, Sci-Hub seems to be a convenient resource, especially for engineers and chemists, as the overrepresentation shows. Lastly, when it comes to the representation of publishers, the Sci-Hub data shows that the academic publishing field is even more of an oligopoly in terms of actual usage when compared to the amount of literature published. Further analysis of how, by whom and where Sci-Hub is used will undoubtedly shed more light onto the practice of academic publishing around the globe.

Data availability
All the data used in this study, as well as the code to analyze the data and create the figures, is archived on Zenodo as Data and Scripts for Looking into Pandora's Box: The Content of Sci-Hub and its Usage (DOI, 10.5281/zenodo.472493) 26 .
In addition the analysis code can also be found on GitHub at http://www.github.com/gedankenstuecke/scihub.

Competing interests
The author uses SciHub regularly in his own research. Otherwise the author declares no competing financial, personal, or professional interests.

Grant information
The author(s) declared that no grants were involved in supporting this work. The analysis of shadow libraries usage data is not a trivial matter, and requires some caution, especially when someone tries to understand the processes that produce these usage numbers. The article is very modest in its aims, and hopes to present only a very basic analysis of the Sci-Hub usage, but I believe more could have been done in terms of the analysis, and more caution should have been used in when offering explanations.

Open Peer Review
During the analysis, I think the logic of Sci-Hub allows us to distinguish between two processes: the one that the collection, and one that the collection. Articles get into the Sci-Hub collection produces consumes when someone bumps into a paywall, and turns to Sci-Hub to circumvent it. This means that the corpus of Sci-Hub is indicative of works that have limited accessibility. When analyzing the corpus, the distribution of publishers, and topics, one should look at it from this perspective, and check, for example the open access policies of the most highly represented publishers, or journals, and analyse the results not just within the sci-hub universe, but against the whole population of articles/journals/publishers/topics, including those with widespread open access policies.
The download numbers, on the other hand, represent the demand for an article. I would argue that articles with only 1 download only inform about the accessibility (someone met a paywall, and downloaded the article from sci-hub), while articles with more than 1 downloads actually suggest some things about the demand (how many individuals were interested in that article/discipline).
On that note I missed the geographic analysis, especially as some data on the location of the download was also available in the original dataset.
Regarding the interpretation of the data. I think the analysis in the Who's reading? section is not substantiated by the data in any manner. On the contrary, while the data covers all downloads, across all the globe, the interpretation relies on a US census. I don't think that is appropriate. Local usage is structured and explained by local characteristics of higher education, research, and economy. One should not generalize a US explanation to the whole dataset.
The analysis in the section is also misleading. It makes claims about the academic publishing Non solus space in general, while the sci-hub data is biased, as it only contains articles with accessibility problems. Articles, journals and publishers with no accessibility problems are probably missing from, or are heavily underrepresented in the dataset, thus one cannot come to any conclusion on the state of academic publishing. Take the case of PLOSone as an example, on why the current analysis is flawed.
publishing. Take the case of PLOSone as an example, on why the current analysis is flawed.
As a result, the validity of the overall conclusions is limited.

Is the work clearly and accurately presented and does it cite the current literature? Yes
Is the study design appropriate and is the work technically sound? Partly

If applicable, is the statistical analysis and its interpretation appropriate? Partly
Are all the source data underlying the results available to ensure full reproducibility? Yes

Are the conclusions drawn adequately supported by the results? Partly
No competing interests were disclosed.

Competing Interests:
I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above. Bastian Greshake has done a good job in presenting his argument and providing supporting documentation. He may want to consider: Mark Ware's 2015 STM Report noted below in regards to the research behaviour & motivation, as there may be information in this report that help further augment why SciHub is used & who is "reading". Greshake's graphs readily illustrate the points he is making regarding regarding the represented journals & publishers. His use of the publicly available data and noting both where the data is located and scripts used in order to perform his study lend to the transparency of his study. Lastly, these findings are of use and interest to librarians and information scientists as well as to product and resource developers looking to develop mechanisms to counter the "SciHub phenomena."

If applicable, is the statistical analysis and its interpretation appropriate? Yes
Are all the source data underlying the results available to ensure full reproducibility? Yes In general, this is a clearly written and argued paper on a developing topic affecting the scholarly communications ecosystem. The author has engaged with much of the recent literature on the topic of which we are aware. The underlying data is freely available and thus possible to replicate. The quantitative analysis proceeds logically and is easy to understand. There are a few areas where we would like to see discussion expanded (noted below) though overall this paper is a very valuable contribution to the literature on this topic.

Specific Criticisms:
The abstract brings up the question of who uses Sci-Hub and why. However, there is relatively little discussion of this in the paper. By our reading of the literature, the question has not been rigorously addressed to date. But some have taken steps toward an answer. Specifically Travis, (2016) is a data point worth discussing < >. (The survey had a http://www.sciencemag.org/news/2016/05/survey-most-give-thumbs-pirated-papers large response rate but should be viewed with the skepticism that would normally apply to any "open" internet survey.) The Supplementary Figures are worth incorporating into the text. S2, in particular, is an informative chart. The Supplementary Figures are worth incorporating into the text. S2, in particular, is an informative chart. It should be improved by matching the colors for each publisher in the legend. That is, "other" should appear as the darkest blue in both bars, rather than being assigned different shades of blue as it is presently. That will allow readers to observe the important differences easily.
Your methods section should include some additional discussion of what you mean by "expected number of downloads for each publisher." You are using "expected" in a mathematical sense that diverges from the word's everyday meaning, so you should spell this out for the reader.
We find the use of the term "Black Open Access" in the discussion section puzzling. "Guerilla open access" is more widely used, as suggested by Google Trends < https://trends.google.com/trends/explore?q=%22black%20open%20access%22,%22guerilla%20open%20access%22 >. Additionally, there are important issues of "respectability politics" to consider here; there are vocal OA advocates and practitioners who condemn Sci-Hub and do not want the OA movement to be associated with it or with copyright violation. Using the word "black" may be interpreted as implying that Sci-Hub is compatible with so-called green and gold OA publishing. Librarians in particular are loath to associate Sci-Hub with the OA movement, due to professional norms that often include upholding intellectual property restrictions on ethical grounds (e.g., < >, http://crln.acrl.org/content/78/2/86.full < >. https://thewinnower.com/papers/3489-signal-not-solution-notes-on-why-sci-hub-will-not-open-access On the other end of the spectrum, Sci-Hub's supporters and sympathizers may object to negative connotations conjured by the term "black." None of the above comments are meant to imply that your usage of "Black Open Access" is wrong. However, if you are going to use the less familiar term, you should explain why and note that this is a contested issue. In the Introduction section, your remarks on Sci-Hub's legal status are well made, but another aspect of this is the fact that credential sharing is explicitly prohibited by many publishers (and some libraries) in their terms of use. This is worth mentioning. Elsevier's and Wiley's Terms are clear on this issue. < > < https://www.elsevier.com/legal/elsevier-website-terms-and-conditions > http://onlinelibrary.wiley.com/termsAndConditions Due to the ambiguous legality of copying factual and educational works under various copyright regimes, we prefer the terms "potentially illegal" or "likely illegal" when describing Sci-Hub's activities. A recent ruling in India, for instance, suggests that Sci-Hub may not violate the law in that country. < https://hughstephensblog.net/2016/09/27/the-indian-high-court-decision-on-delhi-universitys-copy-shop-a-pyrrhic-victo > Also in the Introduction, the citation for the sentence discussing #icanhazpdf refers to Cabanac, 2015. However, #icanhazpdf is mentioned in that article only in passing. A more thorough analysis can be found in Gardner & Gardner, 2015. < > http://eprints.rclis.org/24847/ Bodó deserves to be cited, but there are better sources on long-term changes in the academic publishing industry. Thompson (2005)  We have read this submission. We believe that we have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however we have significant reservations, as outlined above. So far it is not well studied how and why its users are accessing publications through Sci-Hub. This isn't necessarily true. The last year has seen a lot of articles pop up in the science communication and library literature about SciHub and the whys and hows of its use, including last year's widely shared Science article by John Bohannon, which you briefly mention. This statement should be a bit tempered.
Speaking of the whys of Sci-Hub, you discuss the founder's description of how it is done but did not include any discussion from her about why she chose to develop the database. Her main occupation is as a scientist and she chose to develop SciHub because of being unable to access the literature in her field. I think that story is a compelling backdrop to your own research here.
Again, Bohannon's Science article from April 2016 "Who's downloading pirated papers? EVERYONE," gets very little mention in your paper. In any case, it certainly warrants a bit more discussion in your work. What did Bohannon do right in his analysis? Wrong? How does your work build on or diverge from his findings? In addition to Bohannon's work, there have been a number of scholarly communication experts who have explored and written about they hows and whys of Sci-Hub usage, particularly in the library and information science field. I think a review of some of that literature would really help to ground your work.

The analyses presented here suggest that Sci-Hub is used for a variety of reasons, by different
You argue that your study shows that users use Sci-Hub for a "variety of reasons" but I don't populations. know that your research really supports that. Certainly you've shown what is being accessed and revealed interesting findings in terms of disciplinary, publisher, and publication date distribution, but your results can hardly be said to reveal the underlying motivations of users accessing materials from Sci-Hub. You posit some interesting theories that could explain the numbers you found (lack of access because of lack of well-funded institutional affiliation, etc.), but they are just that: theories. I'd be a bit more cautious in the conclusions you draw from your data, as interesting as they may be.

Is the work clearly and accurately presented and does it cite the current literature? Partly
Is the study design appropriate and is the work technically sound?