Wikipedia:Reliable sources

[[Category:Wikipedia wp:rss|Reliable sources]]

Wikipedia articles should use reliable published sources. This page is an attempt to provide guidance about how to identify these. The two policy pages that discuss the need to use sources are Wikipedia:No original research and Wikipedia:Verifiability.

If you can provide useful information to Wikipedia, please do so, but bear in mind that edits for which no reliable references are provided may be deleted by any editor.

What follows is a description of Wikipedia's best practices. Many articles may fall short of this standard until one or more editors devote time and effort to fact-checking and reference-running. (See efforts to identify reliable sources.) In the meantime, readers can still benefit from your contributions, bearing in mind that unsourced edits, or edits relying on inappropriate sources, may be challenged at any time.

There are many ways in which factual errors can be introduced into reports. Keep in mind that most articles are about characterizing the various factions in a dispute. This means that you will be looking for reliable published reports of people's opinions.

Some definitions

Please note the following terms:

• A fact is an actual state of affairs, which can be an historical event, or a social or natural phenomenon. To say of a sentence or proposition that it is true is to say that it refers to a fact.
• An opinion is a view that someone holds, the content of which may or may not be verifiable. However, that a certain person or group holds a certain opinion is a fact, and it may be included in Wikipedia if it can be verified; that is, if you can cite a good source showing that the person or group holds the opinion.
• A primary source is a document or person providing direct evidence of a certain state of affairs; in other words, a source very close to the state of affairs you are writing about. The term most often refers to a document produced by a participant in an event or an observer of that event. It could be an official report, an original letter, a media account by a journalist who actually observed the event, or an autobiography. In general, Wikipedia articles should not depend on primary sources but rather on reliable secondary sources who have made careful use of the primary-source material. Some primary-source material requires training to use correctly, especially on historical topics. Wikipedia articles may use primary sources only if have been published by a reliable publisher e.g. trial transcripts published by a court stenographer, or historic documents that appear in edited collections. We may not use primary sources whose information has not been made available by a reliable publisher. See Wikipedia:No original research.
• A secondary source summarizes one or more primary or secondary sources. Secondary sources produced by scholars and published by scholarly presses are carefully vetted for quality control and can be considered authoritative. A tertiary source usually summarizes secondary sources. Wikipedia is a tertiary source.

When reporting facts, Wikipedia articles should cite sources. There is a wealth of reliable information in tertiary sources such as the Encyclopædia Britannica. Note that unsigned Encyclopedia Britannica, World Book and Encarta articles are written by staff, not by experts, and do not have the same level of credibility. In recent years there has been a proliferation of specialized encyclopedias some in one volume and others multi-volume such as the New Grove and the Dictionary of American Biography. They can be considered authoritative. Older editions such as the 1911 Encyclopædia Britannica often have fuller articles than current editions on some subjects, though there is always the danger that the information is outdated.

When reporting that an opinion is held by a particular individual or group, the best citation will be to a direct quote, citing the source of the quote in full after the sentence (see Harvard referencing) or using a footnote or embedded link if the source is online. See WP:CITE for more details. If there is text, audio, or video available of someone expressing the opinion directly, you may include or transcribe an excerpt, which is allowed under fair use.

Unattributed material

Wikipedians often report as facts things they remember hearing about or reading somewhere, but they don't remember where, and they have no corroborating evidence. It's important to seek reliable sources to verify these types of reports, and if they cannot be verified, any editor may delete or challenge them.

It's always appropriate to ask other editors, "How do you know that?", or "Can you cite your source?" The burden of evidence lies with the editor who has made the edit in question. See Wikipedia:Verifiability, Wikipedia:No original research and Wikipedia:Avoid weasel words, which are policy.

In biographies of living persons

Unverified material that could be construed as critical, negative or harmful in articles about living persons should be removed immediately, and should not be moved to the talk page. The same applies to sections dealing with living persons in other articles. See Wikipedia:Biographies of living persons and Wikipedia:Libel.

Beware false authority

Look out for false claims of authority. Would you trust a plumber to fill your cavities? Likewise, you should not trust someone with a Ph.D. in plant biology to tell you about quantum mechanics or the Arab-Israeli conflict. People with degrees in one field are almost certainly not experts in any other. If a famous professor of chemistry has strong views on a political subject, his fame and authority in his own field are no reason to quote him in any other.

Use sources who have postgraduate degrees or demonstrable published expertise in the field they are discussing. The more reputable ones are affiliated with academic institutions. The most reputable have written textbooks in their field: these authors can be expected to have a broad, authoritative grasp of their subject.

Exceptional claims require exceptional evidence

Certain red flags should prompt editors to examine closely and skeptically 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.

Evaluating sources

• Do they have an agenda or conflict of interest, strong views, or other bias which may color their report? Remember that conflicts of interest are not always explicitly exposed and bias is not always self-evident. However, that a source has strong views is not necessarily a reason not to use it, although editors should avoid using political groups with widely acknowledged extremist views, like Stormfront.org or the Socialist Workers Party. Groups like these may be used as primary sources only as sources about themselves, and even then with caution and sparingly, or about their viewpoints.
• Were they actually there? Be careful to distinguish between descriptions of events by eyewitnesses and by commentators. The former are primary sources; the latter secondary. Both can be reliable.
• Find out what other people say about your sources.
• Have they reported other facts reliably, including on different subjects? Cross-check with what you already know.
• Are the publications available for other editors to check? We provide sources for our readers, so they must be accessible in principle, although not necessarily online.

See Wikipedia:No original research and Wikipedia:Verifiability for more information.

Check multiple independent sources

Psychological experiments have shown that memory and perception are not as reliable as we would like them to be. In one experiment, subjects were shown playing cards with some anomalies. Subjects could usually identify normal cards correctly even if they were displayed for a very short amount of time. But when briefly flashed a black four of hearts, for example, most subjects would, without apparent hesitation or puzzlement, incorrectly identify it as either the four of hearts or the four of spades. Subjects only became aware of the anomalous cards with longer exposures. Subjects who were aware that these strange cards were mixed in with normal cards were also much better at identifying them. ^[1]

Recent scientific experiments have begun to explain how the brain can remember imagined events as if they were real. ^[2][3] Police, judges, and trial lawyers are familiar with the phenomenon that several different people witnessing the same event remember it differently, sometimes including crucial details. A common classroom exercise is to stage a sudden interruption of the class, then ask each student to write an account of what he or she saw. Most people also know that the older a memory is, the less reliable it may be. Recent studies have shown that this may be because memories are overwritten each time we access them. ^[4]

Because conscious and unconscious biases are not always self-evident, you shouldn't necessarily be satisfied with a single source. Find another one and cross-check. If multiple independent sources agree and they have either no strong reason to be biased, or their biases are at cross purposes, then you may have a reliable account.

However, bear in mind that it is not the job of Wikipedians to do original research. We report what reliable publications publish. We do not investigate, or in any other way attempt to evaluate, whether they are right or wrong. See Wikipedia:No original research.

Evaluating secondary sources

• Have they used multiple independent primary sources?
• Do they have an agenda or conflict of interest, strong views, or other bias which may color their report? Remember that conflicts of interest are not always explicitly exposed and bias is not always self-evident. However, that a source has strong views is not necessarily a reason not to use it, although editors should avoid using political groups with widely acknowledged extremist views, like Stormfront.org or the British Socialist Workers Party. Groups like these may be used as primary sources only i.e. as sources about themselves, and even then with caution and sparingly. Extremist groups should not be used as secondary sources.
• Find out what other people say about your sources.
• Have they reported other facts reliably, including on different subjects? Cross-check with what you already know.
• Are they available to other editors to check? If not, inclusion is probably not appropriate. Note, however, that they need not be online; availability through a library is sufficient.

What is an independent secondary source?

Even given the same primary sources, different analysts may come to different conclusions about the facts being reported. In practice, many secondary sources find and use different primary sources in the course of their research. Conscious biases, unconscious biases, and errors are not always self-evident. The best way to expose them is to cross-check with an independent source.

Independent secondary sources:

• There is separate editorial oversight. This means that they have different employers, or different editors (but not necessarily different publishers).
• Have not collaborated in their efforts.
• May have taken their own look at the available primary sources and used their own judgment in evaluating them.

Using online sources

Reliability

Evaluate the reliability of online sources just as you would print or other more traditional sources. Neither online nor print sources deserve an automatic assumption of reliability by virtue of the medium they are printed in. All reports must be evaluated according to the processes and people that created them.

Publications with teams of fact-checkers, reporters, editors, lawyers, and managers — like the New York Times or The Times of London — are likely to be reliable, and are regarded as reputable sources for the purposes of Wikipedia.

At the other end of the reliability scale lie personal websites, weblogs (blogs), bulletin boards, and Usenet posts, which are not acceptable as sources. Rare exceptions may be when a well-known professional person or acknowledged expert in a relevant field has set up a personal website using his or her real name. Even then, we should proceed with caution, because the information has been self-published, which means it has not been subject to any independent form of fact-checking.

Note that Wikipedia itself does not currently meet the reliability guidelines; however, nothing in this guideline is meant to contravene the associated guideline: Wikipedia:Build the web. Wikilink freely.

Bulletin boards and posts to Usenet

Posts to bulletin boards and Usenet, or messages left on blogs, are never acceptable as primary or secondary sources.

This is because we have no way of knowing who has written or posted them.

Personal websites as primary sources

A personal website or blog may be used only as a primary source, i.e., when we are writing about the subject or owner of the website. But even then we should proceed with great caution and should avoid relying on information from the website as a sole source. This is particularly true when the subject is controversial, or has no professional or academic standing.

Personal websites as secondary sources

Personal websites and blogs may never be used as secondary sources.

That is, they may never be used as sources of information about a person or topic other than the owner of the website. The reason personal websites are not used as secondary sources — and as primary sources only with great caution and not as a sole source if the subject is controversial — 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. It is impossible to know which is the case. 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.

Partisan websites

Partisan political and religious sources should be treated with caution, although political bias is not in itself a reason not to use a source. Widely acknowledged extremist political or religious websites — for example, those belonging to Stormfront, Hamas, or the Socialist Workers Party — should never be used as sources for Wikipedia, except as primary sources i.e. in articles discussing the opinions of that organization or the opinions of a larger like-minded group, but even then should be used with great caution, and should not be relied upon as a sole source.

A partisan source can however, be used to establish likely bounds on truth. For instance if an anti-X source says X is a better explanation than Y (on which it has no reason to be biased) then it is likely that X is a better explanation than Y.

Great for easy access

Full-text online sources are preferable to offline sources if they are of similar quality and reliability, because they are easily accessed by other editors who want to check references, and by readers who simply want more information.

If you find a print source that is out of copyright or that is available on compatible licensing terms, add it to Wikisource and link to it there (in addition to the normal scholarly citation). Many significant out-of-copyright books have already been put online by other projects.

Finding a good source may require some effort

Until more authors publish online, and more material is uploaded, some of the most reliable and informative sources are still available only in printed form. If you can't find a good source on the web, try a local library or bookstore.

Sources in languages other than English

Because this is the English Wikipedia, for the convenience of our readers, English-language sources should be provided whenever possible, and should always be used in preference to foreign-language sources (assuming equal quality and reliability). For example, do not use a foreign-language newspaper as a source unless there is no equivalent article in an English-language newspaper. However, foreign-language sources are acceptable in terms of verifiability, subject to the same criteria as English-language sources.

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.

Advice specific to subject area

History

Historical research involves the collection of original or “primary” documents (the job of libraries and archives), the close reading of the documents, and their interpretation in terms of larger historical issues. To be verifiable, research must be based on the primary documents. In recent decades, many more primary documents (such as letters and papers of historical figures) have been made easily available in bound volumes or online. For instance, the Jefferson Papers project at Princeton begun in 1950 has just published volume 30, reaching February 1801. More recently, primary sources have been put online, such as the complete run of the London Times, the New York Times and other major newspapers. Some of these are proprietary and must be accessed through libraries; others such as “Making of America”, publishing of 19th century magazines, are open to the public.

Scholars doing research publish their results in books and journal articles. The books are usually published by university presses or by commercial houses like W.W. Norton and Greenwood which emulate the university press standards. Reputable history books and journal articles always include footnotes and bibliographies giving the sources used in great detail. Most journals contain book reviews by scholars that evaluate the quality of new books, and usually summarize some of their new ideas. The American Historical Review (all fields of history) and Journal of American History (US history) each publish 1000 or more full-length reviews a year. Many of the major journals are online, as far back as 1885, especially through JSTOR.org. A good book or article will spell out the historiographical debates that are ongoing, and alert readers to other major studies.

On many topics, there are different interpretive schools which use the same documents and facts but use different frameworks and come to different conclusions. Useful access points include: scholar.google.com and books.google.com, and (through libraries) ABC-CLIO’s two abstract services, American: History and Life (for journal articles and book reviews dealing with the US and Canada), and Historical Abstracts (for the rest of the world.) Research libraries will hold paper guides to authoritative sources. The most useful is The American Historical Association's Guide to Historical Literature, edited by Mary Beth Norton and Pamela Gerardi 2 vol (1995), which is an annotated bibliography of authoritative sources in all fields of history.

There are many other sources of historical information, but their authority varies. A recent trend is a proliferation of specialized encyclopedias on historical topics. These are edited by experts who commission scholars to write the articles, and then review each article for quality control. They can be considered authoritative for Wikipedia. General encyclopedias, like the Encyclopedia Britannica or Encarta, sometimes have authoritative signed articles written by specialists and including references. However, unsigned entries are written in batches by freelancers and must be used with caution.

College textbooks are updated every few years, are evaluated by many specialists, and usually try to keep abreast of the scholarship, but they are often without footnotes and usually do not spell out the historiographical debates. Textbooks at the K-12 level do not try to be authoritative and should be avoided by Wikipedia editors. Every place has guide books, which usually contain a capsule history of the area, but the great majority do not pretend to be authoritative. On many historical topics there are memoirs and oral histories that specialists consult with caution, for they are filled with stories that people wish to remember — and usually recall without going back to the original documentation. Editors should use them with caution.

The general public mostly gets its history from novels, films, TV shows, or tour guides at various sites. These sources are full of rumor and gossip and false or exaggerated tales. They tend to present rosy-colored histories in which the well-known names are portrayed heroically. Almost always editors can find much more authoritative sources, but they may be useful in adding to the trivia section of articles.

• See also Historiography

Science and medicine

Cite peer-reviewed scientific journals and check community consensus

Scientific journals are the best place to find primary source articles about scientific experiments, including medical studies. The best scientific journals are peer-reviewed, which means that independent experts in the field are asked to (usually anonymously) review articles before they are published. This usually results in corrections and improvement, sometimes substantial. Many articles are excluded from peer-reviewed journals because they report questionable (or perhaps merely unimportant, in the opinion of the editors) results.

The fact that a statement is published in a peer-viewed journal does not make it true.

Even a well-designed experiment or study can produce flawed results. (For example, see the Retracted article on neurotoxicity of ecstasy published in the very prestigious journal Science). The second part of peer review occurs after publication. Colleagues in the field will read the journal article and discuss it in various forums, including other journals in the same field and often later articles in the same journal. They may find evident flaws in the procedure used just by reading the article and applying their experience, or it may take a long process of trying to reproduce the results by similar or completely different means for the scientific community to determine that the original results were corrupted by some undetermined methodological problem, or to rigorously confirm the original result. The most reliable source for scientific information is the prevailing "scientific consensus".

Determining the scientific consensus could be done with a survey of experts in the field, but it can also be accomplished by following the state of discussions in respected journals.

There is sometimes no one prevailing view because the available evidence does not yet point to a single answer. Because Wikipedia not only aims to be accurate, but also useful, it generally tries to explain the theories and empirical justification for each school of thought, with reference to published sources. Editors should not, however, create arguments themselves in favor of, or against, any particular theory or position. See Wikipedia:No original research, which is policy.

Just because something is not an accepted scientific fact, as determined by the prevailing scientific consensus, does not mean that it should not be reported and referenced in Wikipedia.

However, although significant-minority views are welcome in Wikipedia, the views of tiny minorities need not be reported. See Wikipedia:Neutral Point of View. Significant-minority views should be reported as that, and should not be given the same amount of space in an article as the majority view.

Simply make readers aware of any uncertainty or controversy. A well-referenced article will point to specific journal articles or specific theories proposed by specific researchers, rather than: "Some say that... (vague, unattributed theory), but others believe... (vague, unattributed theory)."

Avoid citing the popular press

The popular press generally does not cover science well. Articles in newspapers and popular magazines generally lack the context to judge experimental results. They tend to overemphasize the certainty of any result, for instance presenting a new experimental medicine as the "discovery of the cure" of a disease. Also, newspapers and magazines frequently publish articles about scientific results before those results have been peer-reviewed or reproduced by other experimenters. They also tend not to report adequately on the methodology of scientific work, or the degree of experimental error. Thus, popular newspaper and magazine sources are generally not reliable sources for science and medicine articles.

What can a popular-press article provide? Often, the most useful thing is the name of the head researcher involved in a project, and the name of his or her institution. For instance, a newspaper article quoting Joe Smith of the Woods Hole Oceanographic Institution regarding whales' response to sonar gives you a strong suggestion of where to go to find more: look up his work on the subject. Rather than citing the newspaper article, cite his published papers.

Which science journals are reputable?

A good way to determine which journals are held in high esteem without polling a bunch of scientists is to look at Impact Factor ratings, which track how many times a given journal is cited by articles in other publications. Be aware, however, that these impact factors are not necessarily valid for all academic fields and specialties.

Keep in mind that even a reputable journal may occasionally post a retraction of an experimental result. Articles may be selected on the grounds that they are interesting or highly promising, not merely because they seem reliable.

Evaluating experiments and studies

There are certain techniques that scientists use to prevent results from being contaminated by certain kinds of common errors, and to help others replicate results.

• Experimental control
  • Placebo controls
  • Ensuring demographic information aligns with the general population to check that the sample is sufficiently random
  • Double-blind medical studies
• Present a high degree of detail about the design and implementation of the experiment; don't just present the results.
• Make raw data available; don't just present conclusions.

Statistics

Statistical information is easily and often misinterpreted by the public, by journalists, and by scientists. It should be checked and explained with the utmost care, with reference to published sources.

See Misuse of statistics, Opinion poll, and Statistical survey for common errors and abuses.

Law

First of all, remember that laws are only valid in certain jurisdictions. An expert on Californian and U.S. federal law is not qualified to comment on French or German law. The opinion of local experts is therefore preferred, in general, to that of outside commentators.

Some of the commentary on laws and court decisions is heavily slanted for political purposes, with ample use of hyperbole, which should not be taken at face value. For instance, people opposing certain criminal procedure laws may claim that they "suppress the presumption of innocence" or "suspend the rule of law". Such comments, while they can be reported as opinion, should not be represented as fact.

When discussing legal texts, it is in general better to quote from the text, or quote from reputable jurists, than to quote from newspaper reports, although newspaper reports in good newspapers are acceptable too. The journalist who wrote the paper may not be trained as a lawyer, although s/he may have access to a wider variety of legal experts than many lawyers do, so judge the quality of the report according to how well that journalist, or that newspaper, has covered legal issues in the past.

See also

• Wikipedia:Neutral Point of View, policy
• Wikipedia:No original research, policy
• Wikipedia:Verifiability, policy
• Wikipedia:Cite sources, style guide
• Wikipedia:Check your facts, style guide
• Wikipedia:Common knowledge, guideline

References

1. ^ The playing card experiment is described by Thomas Kuhn in The Structure of Scientific Revolutions (1962), p. 62-64. He cites the following article: J.S. Bruner and Leo Postman, "On the Perception of Incongruity: A Paradigm," Journal of Personality, XVIII (1949), 206-23. Following the advice of this page, the original source should be checked to see if the summary of Kuhn's summary is accurate.
2. ^ False memories based on imagined events: "Biological Basis for False Memories Revealed" by Michelle Trudeau. All Things Considered 23 Oct 2004. [5]
3. ^ "Making False Memories." Talk of the Nation Science Friday. 4 Feb 2005. [6]
4. ^ On overwriting memories each time we access them:

(Currently locating sources.)