Neutral Point of View says that the article should fairly represent all significant viewpoints that have been published by a verifiable source, and should do so in proportion to the prominence of each. Now an important qualification: Articles that compare views need not give minority views as much or as detailed a description as more popular views, and may not include tiny-minority views at all (by example, the article on the Earth only very briefly refers to the Flat Earth theory, a view of a distinct minority). We should not attempt to represent a dispute as if a view held by a small minority deserved as much attention as a majority view, and views that are held by a tiny minority should not be represented except in articles devoted to those views. To give undue weight to a significant-minority view, or to include a tiny-minority view, might be misleading as to the shape of the dispute. Wikipedia aims to present competing views in proportion to their representation among experts on the subject, or among the concerned parties. This applies not only to article text, but to images, external links, categories, and all other material as well.
Undue weight applies to more than just viewpoints. Just as giving undue weight to a viewpoint is not neutral, so is giving undue weight to other verifiable and sourced statements. An article should not give undue weight to any aspects of the subject, but should strive to treat each aspect with a weight appropriate to its significance to the subject. Note that undue weight can be given in several ways, including, but not limited to, depth of detail, quantity of text, prominence of placement, and juxtaposition of statements.
Minority views can receive attention on pages specifically devoted to them—Wikipedia is not paper. But on such pages, though a view may be spelled out in great detail, it should not be represented as the truth.
If a viewpoint is in the majority, then it should be easy to substantiate it with reference to commonly accepted reference texts;
If a viewpoint is held by a significant minority, then it should be easy to name prominent adherents;
If a viewpoint is held by an extremely small (or vastly limited) minority, it does not belong in Wikipedia (except perhaps in some ancillary article) regardless of whether it is true or not; and regardless of whether you can prove it or not.
Views held only by a tiny minority of people should not be represented as significant minority views, and perhaps should not be represented at all.
If you are able to prove something that no one or few currently believe, Wikipedia is not the place to premiere such a proof. Once a proof has been presented and discussed elsewhere, however, it may be referenced. See: Wikipedia:Attribution
Telling the difference between facts and opinions
By "fact" we mean "a piece of information about which there is no serious dispute." Otherwise, in order to be converted to a fact, it will need to be rephrased as an indirect statement.
Reliability should be judged relative to the statement being sourced. Any source can be a reliable source for its own opinion. However, not all sources have relevant opinions. Please do not give the opinions of sources undue weight. Making a statement about a fact other than someone's opinion requires a higher degree of reliability. The more extraordinary the fact, the higher the degree of reliability needed.
Reliability can help judge due weight
The reliability of a source can help you judge the weight to give the opinions of that source. The more reliable the source, the more weight you should give its opinion. For sources of very low reliability, due weight may be no mention at all.
... but it's not perfect
Sources may still have systemic bias problems. If you use only English sources, you will probably represent the points of views of people in English-speaking countries disproportionately. Even if you search for foreign language sources, the opinions of people in countries with low literacy rates will probably still be underrepresented. Using foreign language sources can make fact-checking difficult, as many Wikipedians will not understand them. If you can, find a professional translation.
Ideally, on international topics (like food) we should represent all countries or regions in proportion to their population. In practice, finding sources from foreign countries where the main language is not English, or where there is a low literacy rate, may be difficult. Once foreign sources are found, it may be difficult to evaluate their reputability, since those of us from English-speaking countries are unlikely to be familiar with the publications of non-English-speaking countries.
Aspects of reliability
In assessing the suitability of a source for the purposes of research a number of aspects should be considered.
Main aspects
Editorial oversight—A publication with a declared editorial policy will have greater reliability than one without, since the content is subject to verification. Self published sources such as personal web pages, personally published print runs and blogs have not been subject to any form of independent fact-checking and so have lower levels of reliability than published news sources (The Economist) and others with editorial oversight, which in turn are less reliable than professional or peer-reviewed journals (Nature).
Attributability—The more we know about the originator, either organisation or individual, of source material, the better. This helps us measure the authority of the content:
Expertise of the originator with respect to the subject—An academic expert in one subject is more reliable when writing about that subject than when writing about another. For example, a biologist is more reliable when writing about biology than when writing about nuclear physics.
Bias of the originator with respect to the subject—If an author has some reason to be biased, or admits to being biased, this should be taken into account when reporting their opinion. This may be a sign that information from the source needs to be stated indirectly as the opinion of the author, and not asserted as the truth.
Topic specific criteria—Depending on the topic at hand, certain sources otherwise seen as unreliable may be highly appropriate.
When writing a biography of a living person, self-published web pages or blogs of the subject are a valuable source for information of non-controversial biographical details.
Articles on popular culture sometimes rely on less academic sources for their information.
Other aspects
Replicability—Can the conclusions of the source be reached using the information available or is there any indication of gaps in the thinking or process of derivation. Essentially are there any leaps of faith in the source:
Declaration of sources—A source which is explicit about the data from which it derives its conclusions is more reliable than one which does not, ideally a source should describe the collection process and analysis method.
Confidentiality—Sources which are considered confidential by the originating publisher may hold uncertain authority. Given that the original cannot be used to validate the reference then these should be treated with caution.
Corroboration—Do the conclusions match with other sources in the field which have been derived independently. If two or more independent originators agree, in a reliable manner, then the conclusions become more reliable. Care must be taken to establish that corroboration is indeed independent, to avoid an invalid conclusion based on uncredited origination. Undisputed corroboration among high-reliability sources can help establish something as a fact rather than an opinion.
Recognition by other reliable sources— A source may be considered more reliable if another source which is generally considered reliable cites or recommends it. This can be helpful when you are dealing with a source you are unfamiliar with. Even a refutation by an established reliable source may give the opinion of a low-reliability source enough significance for an article of its own. Also see Wikipedia:Fringe theories.
Age of the source and rate of change of the subject—Where a subject has evolved or changed over time a long standing source may not be accurate with respect to the current situation. To interpret utility one must appreciate how the subject has changed and has that change impacted any of the salient points of the source information. Historical or out of date sources may be used to demonstrate evolution of the subject but should be treated with caution where used to illustrate the subject. Should no newer sources be available it is reasonable to caveat use of sources with an indication of the age and the resulting reduction in reliability.
Persistence—Should a reader go to the cited source to validate a statement, or to gain further understanding of the topic, then the form cited should remain stable, continuing to contain the information used by the editor to support the words. In this sense a book or journal citation is superior to an online source where the link may become broken. Some web resources have editorial policies which lead to a lack of persistence; therefore web citations should be treated with caution. However, the assumed persistence of print references is less applicable to books or publications of limited circulation; such publications are likely to become unavailable and unlikely to be reprinted. While some organisations, such as The British Library, contain extensive records of out of print books, these should not be assumed to be accessible to the majority of Wikipedians, particularly considering geographical concerns.
These issues are particularly pertinent to Wikipedia where various editors involved in an article may have their own expertise or position with respect to the topic. Not all sources are comparable in their reliability with respect to a topic, and some sources will have differing degrees of reliability with respect to the subject in different contexts.
In general, a topic should use the most reliable sources that are available to its editors. Common sense is required to determine what sources to use; this guideline cannot be applied robotically. If you have questions about a source's reliability, discuss with other editors on the article's talk page, or if the source is already used in the article, you can draw attention to it with the {{unreliable}} template.
