Reliability
All sources must comply with the sourcing policies: WP:V and WP:NOR. Material about living persons, whether in biographies or elsewhere, must comply with WP:BLP. All biomedical claims, in any article, should comply with WP:MEDRS; also see WP:MEDMOS for sourcing and formatting expectations in medical articles.
Reliability is a minimal requirement; not all reliable sources will meet the FA quality criterion. Reliability may also be a matter of judgement. In cases of doubt, the onus is on the nominator to show that a source should be considered reliable; hence the question that often occurs in source reviews: "What makes this source reliable"?
The sourcing policies, and the guideline Identifying reliable sources, require that sources be reliably published, either in print form (book, journal, newspaper), audio-visual form (film, video, etc.), or online. Published sources may be primary or secondary and, occasionally, tertiary. (See WP:PSTS for the distinctions.) Articles should, where possible, be based mainly on secondary sources, but the careful use of primary sources is entirely acceptable and even welcome. Tertiary sources are acceptable too, but the use of tertiary sources on a topic served by a large scholarly literature might be something to ask the nominator about.
The key factor in assessing reliability is the publisher. Examples of publishers typically considered reliable include:
- established commercial book publishers, particularly academic publishers;
- academic journals;
- most national and regional newspapers and magazines;
- news organisations such as Reuters and the Associated Press;
- broadcasting organisations such as the BBC and CNN;
- national or international expert bodies, such as the World Health Organization;
- governments and their agencies/departments;
- other public bodies or organisations, e.g. universities, museums, major libraries, professional bodies;
- industrial corporations and other private organisations as sources of information about themselves, but not otherwise (see WP:SPS).
The following are examples of sources not generally considered reliable:
- self-published material (such as books, blogs and personal websites), unless the author is a recognised published expert in the field; see WP:SPS, but also see WP:BLPSPS;
- tabloid journalism, although newspapers known for tabloid journalism may be used for the purpose of directly quoting an article subject;
- fansites.
High quality
In addition to the usual reliability requirement, the text of featured articles must be "verifiable against high-quality reliable sources". Reviewers with some expertise in the subject of the article will more easily be able to determine whether the sources used meet the required quality standard. The general questions on which all reviewers should try to satisfy themselves are:
- Do the sources represent the best available for this particular subject?
- Is the source that supports each point the most appropriate for that point?
- Are the main sources reasonably up-to-date, and therefore likely to represent the most recent scholarship? Older sources, particularly contemporaneous primary sources, are often appropriate, but the nominator may need to explain why they've been chosen.
- In the case of anything contentious, are primary sources being used in accordance with the secondary literature?
- Do the sources appear collectively to provide a comprehensive account of the subject, or is there over-reliance on a particular source or group of like-minded sources? Reviewers should be aware that even the highest-quality sources can be used selectively in a way that affects the neutrality of the article.
Making these judgements takes time, and raising them will sometimes invoke the ire of nominators, but if reviewers have any doubts about sources quality, individually or collectively, they should pursue the matter.