Wikipedia:Reliable sources

Wikipedia articles should be based on reliable published sources. This page is a guideline, not a policy, and is mandatory only insofar as it repeats material from policy pages. The relevant policy on sources is Wikipedia:Attribution.

Any material that is challenged or likely to be challenged needs a source, as do quotations, and the responsibility for finding a source lies with the person who adds or restores the material. Unsourced or poorly sourced edits may be challenged and removed at any time. Sometimes it is better to have no information at all than to have information without a source.

Why use reliable sources?

Sources are used:

• To support an assertion made in an article. Sources used in this manner should be directly referenced for the point that is being supported.
• To give credit to the source, to avoid the appearance of plagiarism or copyright violations. See Wikipedia:Copyrights.

Using reliable sources assures the reader that what is being presented meets the Wikipedia standards for verifiability, originality, and neutrality. Accurate citation allows the reader to go to those sources and gives appropriate credit to the author of the work.

Assessing the reliability of the sources used in an article allows the editor to caveat the statements made, identifying where weaknesses are present and where there may be alternative positions on a statement, with a qualitative opinion presented on the relative arguments based on the quality of sources.

If all the sources for a given statement or topic are of low reliability, this suggests to the reader that the content be treated with a degree of skepticism, and to the editor that the material may not be suitable for inclusion in Wikipedia.

Exceptional claims require exceptional sources

Certain red flags should prompt editors to examine the sources for a given claim.

• Surprising or apparently important claims that are not widely known.
• Surprising or apparently important reports of recent events not covered by reputable news media.
• Reports of a statement by someone that seems out of character, embarrassing, controversial, or against an interest they had previously defended.
• Claims not supported or claims that are contradicted by the prevailing view in the relevant academic community. Be particularly careful when proponents say there is a conspiracy to silence them.

Exceptional claims should be supported by multiple credible and verifiable sources, especially with regard to historical events, politically-charged issues, and biographies of living people.

For guidance related to the creation of entire articles about said topics, see Wikipedia:Fringe theories.

Types of source material

Main page: Wikipedia:Attribution

Three classes of sources exist, each of which can be used within Wikipedia:

• Primary sources are documents or people very close to the situation you are writing about. An eyewitness account of a traffic accident published in a newspaper, and the White House's summary of a president's speech are primary sources. Primary source material that has been published by a reliable source may be used for the purposes of attribution in Wikipedia, but only with care, because it's easy to misuse primary sources. The Bible cannot be used as a source for the claim that Jesus advocated eye removal (Matthew 18:9, Mark 9:47) for his followers, because theologians differ as to how these passages should be interpreted. Edits that rely on primary sources should only make descriptive claims that can be checked by anyone without specialist knowledge.

• Secondary sources are documents or people that summarize other material, usually primary source material. These are academics, journalists, and other researchers, and the papers and books they produce. A journalist's analysis of a traffic accident, or the analysis and commentary of a president's speech, are secondary sources. Wikipedia articles should rely on reliable, published secondary sources wherever possible. This means that we only publish the opinions of reliable authors, and not the opinions of Wikipedians who have read and interpreted primary source material for themselves.

• Tertiary sources are reference books such as dictionaries, general encyclopedias and almanacs. These sources generally lack adequate coverage of the topic to be considered comprehensive where arguments are subtle and nuanced. They generally do not discuss and evaluate alternative interpretations. Tertiary sources used for basic facts such as names, spellings, locations, dates and dimensions do not need to be cited. Tertiary sources used for more substantive facts do need to be cited. Some tertiary sources are more reliable than others, and within any given tertiary source, some articles may be more reliable than others. For example, articles signed by experts in Encyclopaedia Britannica and encyclopedias of similar quality can be regarded as reliable secondary sources instead of tertiary ones. Unsigned articles may be less reliable, but they may be used so long as the encyclopedia is a high quality one.

Often the reliability of a source is not determined by its type, but by how it is used. For example, the diary of a famous politician (a primary source) would probably be reliable as source for a statement of opinion, but might not be reliable as a source for a statement of fact.

Biographies of living persons

Main page: Wikipedia:Biographies of living persons

Unsourced or poorly sourced contentious material about living persons should be removed immediately and should not be moved to the talk page.

Self-published sources

Main page: Wikipedia:Attribution

A self-published source is a published source that has not been subject to any form of independent fact-checking, or where no one stands between the writer and the act of publication. It includes personal websites and books published by vanity presses. Anyone can create a website or pay to have a book published, and then claim to be an expert in a certain field. For that reason, self-published books, personal websites, and blogs are usually not acceptable as sources (see Exceptions below).

Self-published sources as secondary sources

Personal websites, blogs, and other self-published or vanity publications should not be used as secondary sources. That is, they should not be used as sources of information about a person or topic other than the owner of the website, or author of the book. The reason personal websites are not used as secondary sources is that they are usually created by unknown individuals who have no one checking their work. They may be uninformed, misled, pushing an agenda, sloppy, relying on rumor and suspicion, or even insane; or they may be intelligent, careful people sharing their knowledge with the world. Only with independent verification by other sources not holding the same POV is it possible to determine the difference.

Visiting a stranger's personal website is often the online equivalent of reading an unattributed flyer on a lamp post, and should be treated accordingly.

Exceptions

As mentioned above there are a few specific situations in which a self-published source can be considered reliable. These include:

When a well-known, professional researcher writing within his or her field of expertise, or a well-known professional journalist, has produced self-published material, these may be acceptable as sources, so long as his or her work has been previously published by credible, third-party publications. Editors should exercise caution for two reasons: first, if the information on the professional researcher's blog (or self-published equivalent) is really worth reporting, someone else will have done so; second, the information has been self-published, which means it has not been subject to any independent form of fact-checking.

Government officials self-publishing within the scope of their official duties, and using official government channels, but without editorial oversight, are also acceptable primary sources for reporting on the official acts of that person or group.

Self-published sources used as primary sources about themselves

Self-published material, whether published online or as a book or pamphlet, may be used as a primary source of information about the author or the material itself, so long as there is no reasonable doubt who wrote the material, and so long as it is:

• relevant to the self-publisher's notability;
• not contentious;
• not unduly self-serving or self-aggrandizing;
• about the subject only and not about third parties or events not directly related to the subject;

The reputation of the self-publisher is a guide to whether the material rises to the level of notability at all.

Bulletin boards, wikis and posts to Usenet

Posts to bulletin boards, Usenet, and wikis, or comments on blogs, should generally not be used as sources. This is in part because we have no way of knowing who has written or posted them, and in part because there is no editorial oversight or third-party fact-checking. See self-published sources for exceptions.

Extremist sources

Organizations and individuals that are widely acknowledged as extremist, whether of a political, religious or anti-religious, racist, or other nature, should be used only as sources about themselves and their activities in articles about themselves, and even then with caution.

Convenience links

Also see Wikipedia:Convenience links

The term "convenience link" is typically used to indicate a link to a copy of a resource somewhere on the Internet, offered in addition to a formal citation to the same resource in its original format. For example, an editor providing a citation to Adam Smith's famous work The Wealth of Nations might choose to include both a citation to a published copy of the work and a link to the work on the internet, as follows:

Smith, Adam (1904) [1776]. ed. Edwin Cannan (ed.). The Wealth of Nations (Fifth edition ed.). London: Methuen and Co. {{cite book}}: |edition= has extra text (help); |editor= has generic name (help), available at Wikisource

Such links are unique in how reliability is applied. It is important to ensure that the copy being linked is a true copy of the original, without any comments, amendations, edits or changes. When the "convenience link" is hosted by a site that is considered reliable on its own, this is relatively easy to assume. However, when such a link is hosted on a less reliable site, the linked version should be checked for accuracy against the original, or not linked at all if such verification is not possible.

Claims of consensus

Just as underlying facts must be sourced, claims of consensus must be sourced in the presence of differences of opinion. Claims that "most" or "all" scientists, scholars, ministers (or rabbis or imams etc.) of a religious denomination, voters, etc. hold a view require sourcing, particularly on matters that are subject to dispute. In the absence of a reliable source of consensus or majority view, opinions should be identified as those of the sources.

Examples of statistics, subjects and online sources

See Wikipedia:Reliable sources/examples for examples and discussion on the use of statistical data, advice by subject area (including history, physical sciences, mathematics and medicine, law, Business and Commerce, popular culture and fiction), and the use of electronic or online sources.

See also

• Wikipedia:Check your facts, style guide
• Wikipedia:Common knowledge, guideline
• Wikipedia:Independent sources, essay
• Wikipedia:WikiProject Fact and Reference Check
• Wikipedia:Verifiability
• Wikipedia:No original research
• Wikipedia:Citing sources

External links

• How to Read a Primary Source, Reading, Writing, and Researching for History: A Guide for College Students, Patrick Rael, 2004.
• How to Read a Secondary Source, Reading, Writing, and Researching for History: A Guide for College Students, Patrick Rael, 2004.