Wikipedia:Reliable sources
There is general agreement that reliable sources are needed for the facts presented in Wikipedia articles. This page is an attempt to provide guidance about how to identify reliable sources and reliable information.
The best practices which are described here are ideals. Most articles will fall far short of them until one or more editors devote a significant amount of time and effort into fact-checking and reference-running. See #Efforts to identify reliable sources at the bottom of this page for collaborative projects to do just that.
Please note the following terms:
- A fact is some piece of information about the universe, whether that be a historical event, or an ongoing social or natural phenomenon.
- An opinion is a view that someone holds, the content of which may or may not be verifiable. However, the idea that a certain person or group of people holds a certain opinion is a verifiable fact.
- A primary source reports personal observations of the universe (including people, when they are the subject of the report). This may mean that they observe a fact directly, or that they observe indirect evidence of a fact.
- A secondary source summarizes one or more primary sources. A tertiary source summarizes one or more secondary sources.
There are many ways in which factual errors can be introduced into reports. These guidelines are designed to detect and correct these errors for the purpose of properly identifying true and untrue facts in the Wikipedia. Different types of facts may require different methods for determining the truth in a reliable fashion.
Keep in mind that some articles are about characterizing the various factions in a dispute, not to characterize the veracity of the facts underlying the various positions. This means that you will be looking for reliable reports of what may be factually incorrect opinions.
Hearsay
The longer the chain of sources between the reader and the actual event, the more likely it is that mistakes and misrepresentations have crept into the report. The human brain is best at remembering the gist of what it has been told, but usually does not record the exact words. Different authors may also make different assumptions, which are not necessarily explicit and which may cause an incorrect re-interpretation of the events being reported. (What is said or what is intended to have been said is often not what was heard.)
This is why reputable courts of law exclude hearsay. It is a phenomenon demonstrated by the children's game of Telephone. It is also why rumors are considered unreliable and contribute to the creation of some urban legends.
Whenever possible, Wikipedia editors are encouraged to follow the chain of reporting back as far as possible.
Get close to the source
When reporting on objective facts, Wikipedia articles should cite primary and secondary sources whenever they exist. Tertiary and derivative sources should be considered suspect. 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. If there is text, audio, or video available of someone expressing the opinion directly, it is highly preferable to include or transcribe an excerpt (very much allowed under fair use).
Unattributed material
Often Wikipedians will report as facts things that they remember hearing about or reading somewhere, but they don't remember exactly where, and they don't have any other corroborating information. These types of reports are the most important to try to verify.
It's always appropriate to ask other editors, "How do you know that?", or, "Can you cite your sources?" If they didn't have a particular source in mind when they wrote the material originally (including personal experience) someone (probably you or them) will need to some additional research to find a concrete source.
Many popular misconceptions can be rooted out of the encyclopedia in this manner. Even when editors are remembering correct facts, the details are often fuzzy or slightly wrong, and it is enlightening and satisfying for all involved when more exact, reliable information is uncovered.
For advice about dealing with unattributed material when you find it, see Wikipedia:Verifiability and Wikipedia:Confirm queried sources. But also see [#Common_knowledge Common knowledge] below.
Evaluating 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.
- 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.
Check multiple independent sources
It is very important to cross-check primary sources against each other. This will help detect biases and errors.
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 if even 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. Subject 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.[#References 1]
Recent scientific investigations have begun to explain how the brain can remember imagined events as if they were real. [#References 2]
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.
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. [#References 3]
Because conscious and unconscious biases are not always self-evident, you shouldn't necessarily be satisfied with a single primary 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 have a reliable account.
What is an independent primary source?
Independent primary sources:
- Each had direct personal experiences which they are recounting
- Have not discussed their experiences with each other, which could contaminate their memories of events
- Do not have a common influence which could taint their stories in the same way.
Evaluating secondary sources
- Are they actually a secondary source (e.g., have they mainly derived their information from primary 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.
- 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.
Check multiple independent sources
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.
What is an independent secondary source?
Independent secondary sources:
- Have unrelated entities of editorial oversight. This means that they have different employers, different editors, and possibly different publishers.
- Have not collaborated their efforts.
- 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 closely and skeptically examine the sources for a given claim.
- Reports of a statement by someone that seems out of character, embarrassing, controversial, or against interest which 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.
- Claims which strongly support one or another party in an ongoing dispute (see e.g. Wikipedia:List of controversial issues)
Domain-specific advice
Personal opinions
Statements of personal opinion can easily be misheard, misunderstood, misinterpreted, twisted, and sensationalized.
When evaluating reports of such statements, consider whether or not the statement aligns with the views of the speaker as expressed directly by them or as reported in other sources. If you are not familiar with the public views of the person in question, dig around and find out more about them. It may not be apparent that your source is biased or unreliable unless you have some background information to check it against.
Opinions on some subjects are more easily misinterpreted than others. Use your best judgment.
History
Historical events are difficult to verify because they cannot be replicated. We must rely on people's memories, recorded accounts, and physical evidence to reconstruct it.
Evidence and factual accounts contemporary with the events are often more reliable, because these accounts have fewer intermediaries with primary sources (if any).
Many summaries and overviews of history involve a lot of interpretation and analysis, finding patterns and attributing causes. Sometimes later historical analyses of this kind are more reliable, because the passage of time allows more scholarly debate, more reflection, and increases the likelihood that the historian was personally involved in or attached to the events that he or she is analyzing.
Science
(Coming soon.)
Statistics
Statistical information is easily and often misinterpreted by the public, by journalists, and even by scientists. It should be checked and explained with the utmost of care.
See Misuse of statistics, Opinion poll, and Statistical survey for common errors and abuses.
Using online sources
Don't drop your guard
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 just by virtue of the medium they are printed in. All reports must be evaluated according to the processes and people that created them.
Some online sources have strong, reliable editorial processes, as might a reputable newspaper or an academic journal. Many web sites are created by heretofore unknown individuals who have no one checking their work. They may be ignorant, 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. Visiting a stranger's personal web page is often the online equivalent of reading an unattributed flyer on a lamp post, and should be treated accordingly - with significant skepticism.
=Great for easy access
Full-text online sources are preferable to offline sources if they are of similar quality and reliability because they can be more easily accessed by other editors who which 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.
Don't be lazy
Until more authors publish online and more material is uploaded, some of the most reliable and informative sources are still in print. If you can't find a good source on Google, get to your local library or bookstore. They exist for a reason. You'll be amazed what you can learn there.
Efforts to identify reliable sources
- Wikipedia:WikiProject Fact and Reference Check
- Wikipedia:Forum for Encyclopedic Standards
- Wikipedia:Approval mechanism
See also
- Wikipedia:Cite sources (how to)
- Wikipedia:Check your facts (please do)
- Wikipedia:Verifiability
References
- 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.
- False memories based on imagined events:
- On overwriting memories each time we access them:
- (Currently locating sources.)