Wikipedia:Reliable sources
 | This page documents an English Wikipedia content guideline. Editors should generally follow it, though exceptions may apply. Substantive edits to this page should reflect consensus. |
 | This page in a nutshell: Each book, article, or other source needs to be credible for supporting the particular claim(s) it supports. In case of a dispute, editors need to be able to explain why they relied on that source. |
Wikipedia articles should be based on reliable, published sources, making sure that all majority and significant minority views that have appeared in those sources are covered (). If no reliable sources can be found on a topic, Wikipedia should not have an article on it.
This guideline discusses the reliability of various types of sources. The policy on sourcing is Wikipedia:Verifiability, which requires inline citations for any material challenged or likely to be challenged, and for all quotations. The verifiability policy is strictly applied to all material in the mainspace—articles, lists, and sections of articles—without exception, and in particular to biographies of living persons, which states:
Contentious material about living persons (or, in some cases, recently deceased) that is unsourced or poorly sourced—whether the material is negative, positive, neutral, or just questionable—must be removed immediately and without waiting for discussion.
In the event of a contradiction between this guideline and our policies regarding sourcing and attribution, the policies take priority and editors should seek to resolve the discrepancy. Other policies relevant to sourcing are Wikipedia:No original research and Wikipedia:Biographies of living persons. For questions about the reliability of particular sources, see Wikipedia:Reliable sources/Noticeboard.
Overview
Articles should be based on reliable, independent, published sources with a reputation for fact-checking and accuracy. This means that we publish only the analysis, views, and opinions of reliable authors, and not those of Wikipedians, who have read and interpreted primary source material for themselves. The following examples cover only some of the possible types of reliable sources and source reliability issues, and are not intended to be exhaustive. Proper sourcing always depends on context; common sense and editorial judgment are an indispensable part of the process.
Definition of a source
A source is where the material comes from. For example, a source could be a book or a webpage. A source can be reliable or unreliable for the material it is meant to support. Some sources, such as unpublished texts and an editor's own personal experience, are prohibited.
When editors talk about sources that are being cited on Wikipedia, they might be referring to any one of these four concepts:
- The piece of work itself (the article, book)
- The creator of the work (the writer, journalist)
- The publication that contains the work (the journal, newspaper)
- The publisher of the work (for example, Random House or Cambridge University Press)
Any of the four can affect reliability. Reliable sources may be published materials with a reliable publication process, authors who are regarded as authoritative in relation to the subject, or both. These qualifications should be demonstrable to other people.
Definition of published
Published means, for Wikipedia's purposes, any source that was made available to the public in some form. The term is most commonly associated with text materials, either in traditional printed format or online; however, audio, video, and multimedia materials that have been recorded then broadcast, distributed, or archived by a reputable party may also meet the necessary criteria to be considered reliable sources. Like text, media must be produced by a reliable source and be properly cited.
Additionally, an accessible copy of the media must exist. It is convenient, but by no means necessary, for the copy to be accessible via the Internet.
Context matters
The reliability of a source depends on context. Each source must be carefully weighed to judge whether it is reliable for the statement being made in the Wikipedia article and is an appropriate source for that content.
In general, the more people engaged in checking facts, analyzing legal issues, and scrutinizing the writing, the more reliable the publication. Sources should directly support the information as it is presented in the Wikipedia article.
Information provided in passing by an otherwise reliable source or information that is not related to the principal topics of the publication may not be reliable; editors should cite sources focused on the topic at hand where possible. For example, a publisher's web site is likely to be reliable for an author's identity, date of publication, etc., but not necessarily for a critical, artistic, or commercial evaluation of the work .
Age matters
Especially in scientific and academic fields, older sources may be inaccurate because new information has been brought to light, new theories proposed, or vocabulary changed. In areas like politics or fashion, laws or trends may make older claims incorrect. Be sure to check that older sources have not been superseded, especially if it is likely that new discoveries or developments have occurred in the last few years. In particular, newer sources are generally preferred in medicine.
Sometimes sources are too new to use, such as with breaking news (where later reports might be more accurate), and primary sources which purport to debunk a long-standing consensus or introduce a new discovery (in which case awaiting studies that attempt to replicate the discovery might be a good idea, or reviews that validate the methods used to make the discovery).
Sources of any age may be prone to recentism, and this needs to be balanced out by careful editing.
Usage by other sources
How accepted and high-quality reliable sources use a given source provides evidence, positive or negative, for its reliability and reputation. The more widespread and consistent this use is, the stronger the evidence. For example, widespread citation without comment for facts is evidence of a source's reputation and reliability for similar facts, whereas widespread doubts about reliability weigh against it. If outside citation is the main indicator of reliability, particular care should be taken to adhere to other guidelines and policies, and to not unduly represent contentious or minority claims. The goal is to reflect established views of a topic as far as we can determine them.
Some types of sources
Many Wikipedia articles rely on scholarly material. When available, academic and peer-reviewed publications, scholarly monographs, and textbooks are usually the most reliable sources. However, some scholarly material may be outdated, in competition with alternative theories, controversial within the relevant field, or largely ignored by the mainstream academic discourse. Try to cite current scholarly consensus when available, recognizing that this is often absent. Reliable non-academic sources may also be used in articles about scholarly issues, particularly material from high-quality mainstream publications. Deciding which sources are appropriate depends on context. Material should be attributed in-text where sources disagree.
Scholarship
- Prefer secondary sources – Articles should rely on secondary sources whenever possible. For example, a paper reviewing existing research, a review article, monograph, or textbook is often better than a primary research paper. When relying on primary sources, extreme caution is advised. Wikipedians should never interpret the content of primary sources for themselves ().
- Reliable scholarship – Material such as an article, book, monograph, or research paper that has been vetted by the scholarly community is regarded as reliable, where the material has been published in reputable peer-reviewed sources or by well-regarded academic presses.
- Dissertations – Completed dissertations or theses written as part of the requirements for a doctorate, and which are publicly available (most via interlibrary loan or from ProQuest), can be used but care should be exercised, as they are often, in part, primary sources. Some of them will have gone through a process of academic peer reviewing, of varying levels of rigor, but some will not. If possible, use theses that have been cited in the literature, supervised by recognized specialists in the field, or reviewed by independent parties. Unfinished dissertations are generally not reliable sources. Masters dissertations and theses are considered reliable only if they can be shown to have had significant scholarly influence. Some theses are later published in the form of scholarly monographs or peer reviewed articles, and, if available, these are usually preferable to the original thesis as sources.
- Citation counts – One may be able to confirm that discussion of the source has entered mainstream academic discourse by checking what scholarly citations it has received in citation indexes or lists such as DOAJ. Works published in journals not included in appropriate databases, especially in fields well covered by them, might be isolated from mainstream academic discourse, though whether it is appropriate to use will depend on the context. The number of citations may be misleading if an author cites themselves often.
- Isolated studies – Isolated studies are usually considered tentative and may change in the light of further academic research. If the isolated study is a primary source, it should generally not be used if there are secondary sources that cover the same content. The reliability of a single study depends on the field. Avoid undue weight when using single studies in such fields. Studies relating to complex and abstruse fields, such as medicine, are less definitive and should be avoided. Secondary sources, such as meta-analyses, textbooks, and scholarly review articles are preferred when available, so as to provide proper context.
- POV and peer review in journals – Care should be taken with journals that exist mainly to promote a particular point of view. A claim of peer review is not an indication that the journal is respected, or that any meaningful peer review occurs. Journals that are not peer reviewed by the wider academic community should not be considered reliable, except to show the views of the groups represented by those journals.[note 1]
- Predatory journals – Predatory journals are of very low quality and have only token peer-review, if any. These journals publish whatever is submitted if the author is willing to pay a fee. Some go so far as to mimic the names of established journals (Journal hijacking).[1][2][3][4][5] The lack of reliable peer review implies that articles in such journals should at best be treated similarly to self-published sources.[note 2] If you are unsure about the quality of a journal, check that the editorial board is based in a respected accredited university, and that it is included in the relevant high-quality citation index—be wary of indexes that merely list almost all publications, and do not vet the journals they list. ()
- Preprints – Repositories like arXiv, medRxiv, bioRxiv, and Zenodo host non-peer-reviewed self-published sources. These include preprints, which are preliminary versions of articles intended for later publication in peer-reviewed journals, as well as other materials like lecture notes and informal expository writing. These materials are seldom reliable sources, and they are not permitted for medical content. However, they sometimes meet the criteria for acceptable use of self-published sources, and links to such repositories can be used as open-access links for papers which have subsequently been published reliably.
News organizations
News sources often contain both factual content and opinion content. News reporting from well-established news outlets is generally considered to be reliable for statements of fact (though even the most reputable reporting sometimes contains errors). News reporting from less-established outlets is generally considered less reliable for statements of fact. Most newspapers also reprint items from