General Interest FAQs
FAQs for Journals Considering Participation in PMC
What is PubMed Central?
PubMed Central (PMC) is the U.S. National Institutes of Health (NIH) free digital archive of biomedical and life sciences journal literature. Participation by publishers in PMC is voluntary, although participating journals must meet certain editorial and technical standards. PMC, itself, is not a publisher. Access to PMC is free and unrestricted.
Who operates PubMed Central?
PubMed Central was developed and is operated by the National Center for Biotechnology Information (NCBI), a division of the National Library of Medicine (NLM) at the U.S. National Institutes of Health (NIH).
Does any independent group oversee the operation of PubMed Central?
The PubMed Central National Advisory Committee, established in 1999, provides independent advice on the content and operation of PubMed Central. The Committee is responsible for establishing criteria for groups submitting material to the system, and ensuring that PubMed Central remains responsive to the needs of researchers, publishers, librarians, and the general public. Members of the Committee are appointed by the Director of the National Institutes of Health from the biomedical and information communities as well as the general public.
What is the connection between PubMed Central (PMC) and PubMed?
PubMed is a database of citations and abstracts for millions of articles from thousands of journals. It includes links to full-text articles at several thousand journal web sites as well as to most of the articles in PubMed Central.
PubMed Central (PMC) is an electronic archive of full-text journal articles, offering free access to its contents. PMC contains over half a million articles, most of which have a corresponding entry in PubMed.
PubMed does not have citations for certain types of PMC material, such as book reviews, that are considered out of scope for PubMed. These items constitute a small portion of the total PMC collection and there are no plans to include them in PubMed.
In addition, articles published prior to 1966 (and added to PMC via the Back Issue Digitization project) generally will be in PMC for several months before appearing in PubMed. Citations and links for these pre-1966 articles are added to PubMed one journal at a time, after all the back issues for that journal have been added to PMC.
How long has PubMed Central been in existence?
PubMed Central began operating in February 2000 with content from two journals: PNAS: Proceedings of the National Academy of Sciences and Molecular Biology of the Cell.
What journals are currently available in PubMed Central?
See the PMC Journal List for a list of currently available journals.
How current is the material in PubMed Central?
The currency and age of material in PubMed Central varies by journal. Many journals make their content available in PMC as soon as it is published. Others may delay release of content in PMC for anywhere from a few months to a few years after publication, but most provide free access to full text within a year of publication.
How far back in time does the archive reach?
NLM is digitizing the earlier print issues of many of the PMC journals in order to provide online access to the complete run of issues of these journals. PMC has material dating back to mid- to late-1800s or early 1900s for some journals.
How can I find out when PubMed Central adds a new journal to its list or adds a large number of back issues for an existing journal?
If you add your name to the PMC News list, we will notify you by email whenever PMC makes these kinds of additions. Please use the link above to add your name to the list. Sending a “subscribe” email message to PMC will not work.
Who may contribute to PubMed Central?
PubMed Central will accept material from any life sciences journal that meets NLM's standards for the archive. A journal must qualify on two levels: on the scientific and editorial quality of its content, and on the technical quality of its digital files. See How to Join PubMed Central for details.
Certain research funding agencies also have policies (NIH Public Access and Wellcome Trust Open Access) that designate PMC as the repository for articles arising out of research funded by them. In these cases, PMC will accept applicable articles directly from eligible researchers. These individuals frequently deposit their final, peer reviewed author manuscripts. Read about the differences between an author manuscript and the final published version of an article in PMC.
Does PubMed Central include research that has not been peer reviewed?
No, PubMed Central does not include any unreviewed research articles.
What types of material may be deposited in PubMed Central?
As an archive, PMC strives to collect and preserve everything that is published in a participating journal. It has a cover-to-cover digital copy of any early issues of a journal that come into PMC through NLM's digitization program. For more recent material, which a journal must supply in XML or SGML form, PMC accepts any editorial content that can be represented accurately with the NLM Journal Publishing XML DTD or a compatible DTD. In this context, “editorial content” refers to articles and article-like items, including book reviews, news items and obituaries.
Journals also contain what may be classified loosely as administrative content — editorial board and staff lists, instructions to authors, notices and announcements, and advertisements. At present, such content usually is available only in print or on an HTML page on a journal's web site. Few, if any, journals have it in XML form. We are developing XML tagging guidelines so that the administrative content can be included in the PMC archive as well. In the meantime, PMC will accept certain administrative items, if the journal publishes them in an article form and can provide suitable full-text XML. For example, see the instructions to authors that the Journal of Virology publishes as an article in its first issue of the year. PMC currently also accepts journal cover images.
For now, PMC will not accept promotional material for pharmaceutical or other products, even if presented in the form of an article. This policy may change when the guidelines for handling administrative content have been completed and it is possible to make a clear distinction for users between legitimate journal articles and promotional material.
In general, a participating journal must deposit in PMC the final, published version of an article as it appears on the journal's own web site. However, in the instance where PMC serves as the repository for a funding agency's access program, PMC will accept an author's final, peer reviewed manuscript of an article. See Who may contribute to PubMed Central?
Why does PubMed Central contain less than the complete contents of some journals?
Most participating journals include all their content in PMC, but a few have chosen to deposit only their primary research articles. PMC also has agreements with certain publishers who deposit only those articles that fall under an open access or similar program covering selected articles from a range of journals. Examples of such programs are Blackwell Publishing's Online Open, Oxford Journals' Oxford Open, and Springer's Open Choice. For such programs, PMC may have only a few articles each from a number of different journals. (Note that these partial participation journals do not appear in the PMC Journal List.)
In addition, the NIH Public Access policy and the Wellcome Trust Open Access policy designate PMC as a repository for articles arising out of research funded by these organizations. Here again, PMC only has selected articles from many different journals and these journals are not included in the PMC journal list.
Does PubMed Central include articles written in languages other than English?
Almost all the material now in PMC is in English. A few journals in PMC publish material in more than one language. For instance, CMAJ, the Canadian Medical Association Journal, has articles in French and English. In this case, only the English material appears in PMC's primary presentation of an article — the HTML full-text display. However, the journal's PDF version of the article, which is also available in PMC, may contain material in French as well as English. For older issues of the journal, which have been scanned under NLM's digitization program, PMC has the complete contents of each issue. That includes articles published exclusively in French.
In order to provide fuller coverage of non-English language material, PMC must be able to ensure proper validation of the archival XML record in these languages. NLM is considering possible collaborations with national agencies in other countries, as well as other methods, to obtain the non-English language expertise needed to provide an adequate level of quality control for the PMC archive.
How is PubMed Central related to PMC International and portable PMC?
PMC International (PMCI) is a collaborative effort between NLM, the publishers whose journal content makes up the PMC archive, and organizations in other countries that share NLM's interest in archiving life sciences literature. The plan is that NLM will distribute content from PMC to other archives, with the permission of the participating publishers. The other archives will use this content to operate PMCI web sites that are similar to the U. S. PMC site. Portable PMC (pPMC) is a version of the PMC software that has been developed by NCBI for use by PMCI sites. Read more about PMCI and pPMC.
May a publisher provide only a subset of its articles or journal content to PubMed Central?
Every journal that is accepted into PMC is encouraged to deposit its complete contents (original research, review articles, commentaries, editorials, letters, news items, etc.) in order to create a credible digital archive of the journal. A journal may choose to exclude certain types of material but, in most cases, must deposit all its primary research content, at a minimum.
The exception to this minimum requirement occurs in the case where a publisher agrees to deposit all articles that fall under an open access or similar program covering selected articles from a range of journals. Examples of such programs are Blackwell Publishing's Online Open, Oxford Journals' Oxford Open, and Springer's Open Choice.
How soon after publication must articles be made available through PubMed Central?
Journals are encouraged to make their content viewable in PMC at the time of publication, or soon after, but may choose to delay release in PMC for up to a year or more. See the Deposit and Access Policies for further guidelines on acceptable delay periods.
Who controls copyright privileges for the material archived in PubMed Central?
Copyright to all material deposited in PMC remains with the publisher or individual authors, whichever is applicable. PMC is simply an archive and does not claim copyright on any material in the archive.
Can publishers continue to provide journal content on other sites in addition to PMC?
A publisher participating in PMC is free to distribute its journal content in any other manner, including through other web sites. In fact, PMC will provide a publisher a copy of its content from the archive, at any time, to be used however the publisher chooses.
In what electronic formats may data be submitted to PubMed Central?
A journal must provide PubMed Central the full text of articles in an XML or SGML format that conforms to an acceptable journal article DTD (Document Type Definition). The original high-resolution, digital image files must also be provided for all figures. A PDF may be submitted in addition to the XML/SGML version of an article, but not as the primary (or only) form. Supplementary material in the form of video, audio or data files may also be submitted. PMC does not accept articles in HTML format.
Does PubMed Central have its own DTD? Must data be submitted in this format?
NLM has a Journal Publishing XML DTD that any journal may use to submit its data. PMC will also accept data in other full-text article DTDs that are widely used in life sciences journal publishing.
Must a journal include PDF versions of its articles in PubMed Central?
PubMed Central prefers a journal to include a PDF version of its articles in the archive. PDFs are not required if a journal does not have them.
How can a journal be sure that PubMed Central will not alter the substance or meaning of submitted content?
PubMed Central does not change the content of submitted articles in any way. Experience to date suggests that participation in PMC may actually improve the quality of a journal's digital archival record, because PMC does an independent check of the accuracy of the XML/SGML and related files. The initial setup for a journal in PMC involves a thorough automated and manual review of the journal's content to ensure the accuracy of the material. The publisher is also asked to review its content in PMC before a journal is released to the public initially. PMC's checking includes a comparison of the content in PMC to that at the journal's own web site and/or to a print copy of the journal. When discrepancies are found, the publisher is asked to provide corrected files to PMC, precisely because PMC does not want to make any changes to the publisher's content itself. Content deposited after the journal is live in PMC is verified and corrected in a similar manner.
PMC's approach to archiving adds a further, and significant, level of quality assurance. Every time a user asks to see an article in PMC, the online (HTML) view of that article is created on the spot, directly from a copy of the archival files — XML, image files, etc. PMC does not maintain a static HTML display of an article. Thus, every person who requests and reads an article in PMC is verifying the integrity of the archived files.
How much work is required of a publisher to prepare journal content for PubMed Central?
Many journals already create XML or SGML versions of their articles as part of the journal production process. These journals must only arrange to transmit their XML/SGML files to PMC together with associated image files and, as appropriate, PDFs and supplementary data files. Some additional work may be needed, initially, to refine the journal's process for creating XML/SGML, if the submitted data does not satisfy PMC's technical standards..
A journal that does not currently produce XML or SGML versions of its articles would have to add this process to its production stream or contract with a vendor to create XML from the article source files.
What is the cost of participating in PubMed Central?
PubMed Central charges publishers nothing for including journal content in the PMC archive. A publisher is responsible for any costs it may incur in creating files that meet PMC's technical standards and transmitting them to PMC.
What does a journal gain by depositing its content in PubMed Central?
A journal gets the benefit of a permanent and freely accessible archive, managed by the National Library of Medicine, at almost no cost to the publisher — merely what it costs to provide PMC a copy of its material. More established journals also benefit from NLM's Back Issue Digitization program. Every journal can request from NLM and receive, free, a copy of its archived content at any time.
NLM's experience in digital journal archiving is evident in its development of the publicly available Journal Archiving and Interchange XML DTD. The DTD has been endorsed by the US Library of Congress and the British Library as a standard for digital journal archiving. It also has been adopted by a number of publishers and other archives. Continued development of the DTD and related tools is actively supported by an advisory committee of XML experts representing the publishing, archiving, and software development communities.
Participation in PMC usually improves the overall level of quality of a journal's archival files, as explained in the answer to a related FAQ. The journal also benefits from the integration of its full text with PubMed and the numerous other bibliographic and factual databases in NCBI's Entrez system, and the increased exposure that this brings.
Why is PubMed Central needed when many publishers already make their journals freely available on the web within a year of publication?
PubMed Central exists for two reasons, both of which arise from NLM's Congressional mandate: 1) to permanently preserve digital journal literature in the life sciences, and 2) to improve access to biomedical information for health professionals, researchers and the public.
PMC gathers the content from its diverse journal sources into a single repository, where it is stored in a uniform and well defined structured format, the NLM Journal Archiving and Interchange XML DTD. The common format makes it easier to work with the material and extend its utility in efficient ways, using computational techniques. It allows greater integration of the literature with related resources, such as the variety of databases available in NCBI's Entrez system. New features can be applied consistently across the collection in a scalable manner. Once a technique has been developed, there is little extra cost to handle increased amounts of content. Experience has shown that this integration of information resources leads users to new knowledge and stimulates scientific discovery.
PMC presents material to the user in a uniform style while still clearly maintaining the identity of each journal.
Why does PubMed Central require the deposit of complete articles, rather than linking to a journal site for full text?
NLM's journal abstract database, PubMed, already has links to full text at the online sites of thousands of journals that participate in the freely available LinkOut service. One of the primary goals of PMC is the creation of a digital archive of journal literature which, by definition, means the full text must be deposited in PMC. See the answers to the preceding questions to learn about some of the benefits of depositing content in PMC.
What kinds of links does PubMed Central provide from its site to a journal site?
PubMed Central displays a journal banner — a graphic supplied by the journal — at the top of every page that has content from the journal. Although the banner may not include commercial advertising, it can have links to various pages at the journal site. Some banners even provide a link from the full text of an article in PMC to the corresponding article at the journal site. See PLoS Biology, for example.
A journal has the option to include a link from PMC's general copyright notice to a more specific statement of terms and conditions of use posted on the journal site. PMC also offers the option of a journal home page that contains a brief description of the journal, as well as a list of links to the journal site. See Microbiology and Molecular Biology Reviews, for example.
What kinds of usage statistics does PubMed Central provide to participating journals?
Each publisher has password-controlled access to a web site that has usage reports for that publisher's journal(s). The reports, updated daily and aggregated by month, include counts of available articles, total access by type of page (table of contents, abstract, full-text HTML, PDF, etc.) unique IP addresses, and most frequently retrieved or cited articles. Line graphs of each measure supplement the reports. Any report may also be downloaded as a CSV file, for analysis with a spreadsheet package such as Microsoft Excel. PMC also provides a CSV file each month, with usage for the month at the article level.
PMC's usage reports generally contain all information called for in the COUNTER specification, except that PMC does not report use by specific institutions. NLM's privacy policy prevents the reporting of use at an individual or organizational level.
How does a journal join PubMed Central?
See How to Join PubMed Central.
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