Psychology.wiki:Verifiability

The threshold for inclusion in Wikipedia is verifiability, not truth. "Verifiable" in this context means that any reader should be able to check that material added to Wikipedia has already been published by a reliable source. Editors should provide a reliable source for quotations and for any material that is challenged or is likely to be challenged, or it may be removed.

Verifiability is one of Wikipedia's core content policies. The others include No original research and Neutral point of view. Jointly, these policies determine the type and quality of material that is acceptable in Wikipedia articles. They should not be interpreted in isolation from one another, and editors should try to familiarize themselves with all three.

Burden of evidence

 * For how to write citations, see Citing sources

The burden of evidence lies with the editor who adds or restores material. All quotations and any material challenged or likely to be challenged should be attributed to a reliable, published source using an inline citation. The source should be cited clearly and precisely to enable readers to find the text that supports the article content in question.

If no reliable, third-party sources can be found for an article topic, Wikipedia should not have an article on it.

Any edit lacking a reliable source may be removed, but editors may object if you remove material without giving them a chance to provide references. If you want to request a source for an unsourced statement, consider moving it to the talk page. Alternatively, you may tag a sentence by adding the fact template, a section with unreferencedsection, or the article with refimprove or unreferenced. Use the edit summary to give an explanation of your edit. You may also leave a note on the talk page or an invisible HTML comment on the article page.

Do not leave unsourced information in articles for too long, or at all in the case of information about living persons. As Jimmy Wales has put it:

Reliable sources
Articles should rely on reliable, third-party published sources with a reputation for fact-checking and accuracy. Reliable sources are necessary both to substantiate material within articles and to give credit to authors and publishers in order to avoid plagiarism and copyright violations. Sources should directly support the information as it is presented in an article and should be appropriate to the claims made: exceptional claims require exceptional sources.

All articles must adhere to Wikipedia's neutrality policy, fairly representing all majority and significant-minority viewpoints that have been published by reliable sources, in rough proportion to the prominence of each view. Tiny-minority views and fringe theories need not be included, except in articles devoted to them.

In general, the most reliable sources are peer-reviewed journals and books published in university presses; university-level textbooks; magazines, journals, and books published by respected publishing houses; and mainstream newspapers. As a rule of thumb, the greater the degree of scrutiny involved in checking facts, analyzing legal issues, and scrutinizing the evidence and arguments of a particular work, the more reliable it is.

Academic and peer-reviewed publications are highly valued and usually the most reliable sources in areas where they are available, such as history, medicine and science. Material from reliable non-academic sources may also be used in these areas, particularly if they are respected mainstream publications. The appropriateness of any source always depends on the context. Where there is disagreement between sources, their views should be clearly attributed in the text.

For a guideline discussing the reliability of particular types of sources, see Reliable sources (WP:RS). Because policies take precedence over guidelines, in the case of an inconsistency between this page and that one, this page has priority, and WP:RS should be updated accordingly. To discuss the reliability of specific sources, consult the Reliable sources/Noticeboard.

Questionable sources
Questionable sources are those with a poor reputation for fact-checking. Such sources include websites and publications that express views that are widely acknowledged as extremist, are promotional in nature, or rely heavily on rumors and personal opinions. Questionable sources should only be used in articles about themselves. (See below.) Articles about such sources should not repeat any contentious claims the source has made about third parties, unless those claims have also been published by reliable sources.

Self-published sources (online and paper)
Anyone can create a website or pay to have a book published, then claim to be an expert in a certain field. For that reason, self-published books, personal websites, and blogs are largely not acceptable as sources.

Self-published material may, in some circumstances, be acceptable when produced by an established expert on the topic of the article whose work in the relevant field has previously been published by reliable third-party publications. However, caution should be exercised when using such sources: if the information in question is really worth reporting, someone else is likely to have done so.

Self-published sources should never be used as third-party sources about living persons, even if the author is a well-known professional researcher or writer; see WP:BLP.

Articles and posts on Wikipedia should never be used as third-party sources.

Self-published and questionable sources in articles about themselves
Material from self-published and questionable sources may be used as sources in articles about themselves, so long as:
 * it is relevant to their notability;
 * it is not contentious;
 * it is not unduly self-serving;
 * it does not involve claims about third parties;
 * it does not involve claims about events not directly related to the subject;
 * there is no reasonable doubt as to who wrote it;
 * the article is not based primarily on such sources.

Non-English sources
Because this is the English Wikipedia, for the convenience of our readers, English-language sources should be used in preference to foreign-language sources, assuming the availability of an English-language source of equal quality, so that readers can easily verify that the source material has been used correctly.

Keep in mind that translations are subject to error, whether performed by a Wikipedia editor or a professional, published translator. In principle, readers should have the opportunity to verify for themselves what the original material actually said, that it was published by a credible source, and that it was translated correctly.

Therefore, when the original material is in a language other than English:
 * Where sources are directly quoted, published translations are generally preferred over editors performing their own translations directly.
 * Where editors use their own English translation of a non-English source as a quote in an article, there should be clear citation of the foreign-language original, so that readers can check what the original source said and the accuracy of the translation.

Exceptional claims require exceptional sources
Certain red flags should prompt editors to examine the sources for a given claim: Exceptional claims should be supported by the best sources, and preferably multiple reliable sources, especially regarding scientific or medical topics, historical events, politically charged issues, and biographies of living people.
 * surprising or apparently important claims that are not widely known;
 * surprising or apparently important reports of historical events not covered by mainstream news media or historiography;
 * 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 of such claims say there is a conspiracy to silence them.