Assert facts edit
Assert facts, including facts about opinions—but do not assert the opinions themselves.
Objective facts which can be verified in reliable sources, and about which there is no serious dispute, can be asserted directly in Wikipedia articles. For example, that there is a planet called Mars, that a survey produced a certain published result, and that Plato was a philosopher are all objective facts, and can simply be stated without any need for an inline qualifier of the type "John Doe believes...".
On the other hand, statements which express a value or opinion, or objective facts about which there is serious dispute, should not be made directly (as if in Wikipedia's voice). For example, an article should not assert directly that stealing is wrong, or that The Beatles were the greatest band in history (both opinions), or that O. J. Simpson did not kill his ex-wife (an objective fact about which there is dispute).
It is perfectly acceptable, however, to state the fact that a person, organization, group of persons, or percentage of persons holds a particular opinion. For example: "Rolling Stone magazine has said that the Beatles were the greatest band ever" (citing a particular issue of the magazine as a source), "A 1999 survey showed that 90% of Liverpudlians consider the Beatles the greatest band ever" (again, citing a source where the survey results were published), or "Simpson denies killing his ex-wife" (citing a source which reports this denial).
Avoid presenting opinions merely by stating "some people believe...", a practice referred to as "mass attribution".[1] A reliable source supporting a statement that a group holds an opinion must accurately describe how large this group is. Alternatively, attribute the opinion to a specific person or organization.
Don't misrepresent the relative prominence of views reported.
In attributing competing views, it is necessary to ensure that the attribution adequately reflects the relative levels of support for those views, and that it does not give a false impression of parity. For example, to state that "according to Simon Wiesenthal, the Holocaust was a program of extermination of the Jewish people in Germany, but David Irving disputes this analysis" would be to give apparent parity between the supermajority view and a tiny minority view by assigning each to a single activist in the field. To fairly represent all the leading views in a dispute it is sometimes necessary to qualify the description of an opinion, or to present several formulations of this opinion and attribute them to specific groups.
A careful selection of reliable sources is also critical for producing articles with a neutral point of view. Including the facts on which competing opinions are based will help a reader evaluate the credibility of the competing viewpoints. This should be done without implying that any one of the opinions is correct.