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 credible 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 some 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 provides direct evidence for a certain state of affairs. This may mean that the source observes a state of affairs directly, or that they observe indirect evidence of it. In other words, a primary source is a source very close to the original state of affairs you are writing about. An example of primary-source material would be a photograph of a car accident taken by an eye witness, or a report from that eye witness. A trial transcript is also primary-source material. Wikipedia articles may rely on primary sources so long as what they say has been published by a credible publication. For example, a trial transcript has been published by the court. We may not use primary sources whose information has not been made available by a credible publication. See Wikipedia:No original research.

• A secondary source summarizes one or more primary or secondary sources. A tertiary source usually summarizes secondary sources. Wikipedia is a tertiary source.

Get close to the source

When reporting facts, Wikipedia articles should cite sources. There is a wealth of reliable information in articles signed by experts that appear in tertiary sources like reputable encyclopedias, such as the Encyclopædia Britannica, as well as reputable specialized encyclopedias such as the New Grove and the Dictionary of National Biography. Note that unsigned encyclopedia articles are written by staff, not by experts, and do not have the same level of credibility. 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.

If suspect sources have references, follow them. If there are no references, or if the references provided are insufficient, you may need to do additional research, or reconsider the reliability of the report.

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. If there is text, audio, or video available of someone expressing the opinion directly, it is preferable to 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 don't have any other corroborating information. It's important to seek credible sources to verify these types of reports, and if they cannot be verified, any editor may delete them.

It's always appropriate to ask other editors, "How do you know that?", or "Can you cite your source?" If they didn't have a particular source in mind when they wrote the material originally, someone will have to find a credible source. The burden of evidence lies with the editor who has made the edit in question.

For advice about dealing with unattributed material when you find it, see Wikipedia:Verifiability, Wikipedia:No original research and Wikipedia:Avoid weasel words which are policy, and Wikipedia:Cite sources, which is a style guide.

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 i.e. as sources about themselves, and even then with caution and sparingly.
• 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 (in our capacity as Wikipedians) investigate 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, though 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.

Exceptional claims require exceptional evidence

Certain "red flags" should prompt editors to examine closely and skeptically the sources for a given claim.

• Reports of a statement by someone that seems out of character, embarrassing, controversial, or against an interest they had previously defended.
• Surprising or important facts which are not widely known.
• Surprising or important recent events which have not been reported by reputable news media.
• Claims which are not supported, or which are contradicted, by the prevailing view in the scientific community. This is especially true of claims whose proponents consider that there is a conspiracy of "official science" to silence them.
• Claims which strongly support one or another party in an ongoing dispute (see e.g. Wikipedia:List of controversial issues).

Note that none of the above would necessarily exclude a source from being used. Allowances should be made to distinguish between notability and newsworthiness.

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. Historians stress that all verifiable research must be based on the primary documents. This has been aided enormously in recent decades by “letterpress” editions of the documents associated with major figures or episodes, especially in diplomatic and political history. Often these editions run to 10 or more large volumes published over a period of decades. Thus the [Jefferson Papers] project at Princeton begun in 1950 has just published volume 30, reaching February 1801, two weeks before Jefferson was inaugurated president. In the last decade vast primary sources have come on-line, and can be searched, such as the complete run of the London Times, the New York Times and other major newspapers through PROQUEST. Some of the projects are proprietary and must be accessed through libraries, while others such as the “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. These standards include a format that includes footnotes and bibliographies pointing in great detail to the sources used. Even more important the books are evaluated by panels of scholars and specialists as quality control, and manuscripts that do not meet current scholarly standards do not get published. Over 1000 scholarly journals publish history articles, after vetting by scholarly editors and outside experts. 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.com Information contained in scholarly books and articles can be considered authoritative for Wikipedia. A good book or article will spell out the historiographical debates that are ongoing, and alert readers to other major studies. Keep in mind that on many topics there are different interpretive schools which use the same documents and facts but use different frameworks to 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 encyclopedia like recent editions of the Encyclopedia Britannica or Encarta sometimes have authoritative signed articles written by specialists and including references. Be warned that most unsigned entries are written in batches by freelancers with little expertise 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 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. 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 self-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)."

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.

Beware false authority

Would you trust a plumber to fill your cavities? Likewise, you should probably not trust someone who has a Ph.D. in plant biology to tell you about quantum mechanics. Just as actors in TV commercials don white lab coats to make viewers think they are serious scientists, people with degrees in one field are not necessarily experts in any other. Watch out for false claims of authority.

Try to use sources who have degrees in the field they are discussing. The more reputable ones are affiliated with academic institutions. The most reputable have written textbooks in their field for the undergraduate level or higher: these authors can be expected to have a broad, authoritative grasp of their subject.

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.

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.

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. Another possible exception to this rule occurs when somebody had written secondary source material that is suitable as a reference that he now refutes or corrects on his personal website, though even in this case one should be careful and try to find out the reason why the material has not been published elsewhere.

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 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.

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. This can at times be a surprisingly fruitful endeavour.

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. 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.

Efforts to identify reliable sources

• Wikipedia:WikiProject Fact and Reference Check
• Wikipedia:Forum for Encyclopedic Standards
• Wikipedia:Approval mechanism

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.)