This is an essay on Wikipedia essays.
Source checking is a critical part of the WP:FAC review process. The purpose of this essay is to help editors carry out effective source reviews; article authors may also find the advice helpful.
All Wikipedia articles should be based on reliable sources, but at FAC the bar is set higher. The featured-article criteria (FACR) require articles to be "a thorough and representative survey of the relevant literature" (point 1c), and sources to be not only reliable but of high quality (1c). In addition, the citations must be formatted consistently throughout (2c). It is the task of the source reviewer to see that these criteria are observed.
The concept of "high quality" has to be flexibly applied. In some areas—major historical events, biographies of world figures, etc.—the relevant literature is vast, and high-quality sources are plentiful. In other cases, particularly in the various fields of sport or popular culture, "high quality" often has to be interpreted as "best available".
At FAC it is practice to require that every material statement, unless self-evidently true, be supported by a citation, not only material likely to be challenged (per WP:V). Where a cited source does not support the text, that source should be replaced or the text altered to reflect what the source says.
Source reviewers are expected to make clear that they have fully evaluated the article on both the criteria given below:
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:
The following are examples of sources not generally considered reliable:
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:
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.
Every cited statement in an article must be capable of being checked from the source. This does not mean that they must be available to all online. Although verification is obviously easier for web-based sources, print sources must be ultimately verifiable to anyone willing to chase down a book or article. This means that books, newspapers, magazine and journal articles must be defined as precisely as possible; see the format section below.
Google Books links are often used for book sources. If Google Books makes the cited pages available, this is useful. Otherwise, the link may do nothing more than verify that the book exists. Some editors, nonetheless, are very fond of using them, but they are not essential.
Reviewers should carry out spot checks to ensure that sources have been used appropriately, that the sources do indeed support the text, and that the article contains no plagiarism, including close paraphrasing without in-text attribution. The extent to which spot checks are pursued is a matter for each reviewer. It is unreasonable to expect a reviewer to test each cited statement against its source; the volume of citations and the non-accessibility of many print sources make this infeasible. The FAC coordinators will usually require spot-checking for first-time nominations.
Sourcing information should be presented in a consistent and uniform style; the increasing use of cite templates has made this easier to check. This part of the review is the most mechanical, but it should not be skimped. Certain tools have been developed to assist this process, and some of these can be found in the toolbox which appears top right in every FAC nomination. (The external links checker claims to be "over 98% accurate".)
publisher=in their source details, but this is not generally necessary.
If you have questions, please ask for help at WT:FAC.
Although written with FAC in mind, the principles may be usefully applied to other featured content, e.g. Wikipedia:Featured list candidates. Here are some useful links: