Quality control is essential to Wikipedia. To maintain articles of acceptable quality, it is necessary to improve the quality of existing material, and remove material of irreparably poor quality.
This article discusses aspects of quality control at Wikipedia which are used in developing and guiding policies and procedures at Wikipedia directed at article development. An important distinction is made between the editing of the content of articles to maintain quality, and, the conduct of editors involved in the improvement and enhancement of articles written for Wikipedia. The very wiki-nature of Wikipedia enables instant and continuous quality control, by allowing all editors in good standing to participate in improving articles and the encyclopedia as a whole. If someone comes across an error while reading Wikipedia, he or she can immediately and directly change it – by clicking on the Edit tab at the top of the screen, and then by typing away in the edit window that appears. While there are a few bad apples who abuse this privilege by vandalizing or propagandizing, the vast majority of people who edit Wikipedia compose articles responsibly with the common good of humankind at heart – Wikipedia is a public resource intended to make knowledge freely available to everyone in the world, and most participants take this very seriously.
But mistakes do occur. These, and the damage done by the bad apples mentioned above, need continuous attention. The three ways that Wikipedia maintains its quality control is as follows: (a) A great deal of Wikipedia's volunteers' effort is applied to quality control. Wikipedia has an elaborate disciplinary system for handling vandals and other troublemakers, and a dedicated force of system administrators to enforce the Wikipedia community's decisions and policies – admins even have the power to block a bad apple permanently. (b) Once material is added to Wikipedia, an army of volunteers organized under various departments check and recheck it to make sure it conforms to the high standards set forth in Wikipedia's policies and guidelines (which were established specifically with the creation of quality articles in mind). There are departments for everything from typos to factual errors. For a list, see Wikipedia:Maintenance. (c) And Wikipedia even has robots, automated users that monitor for errors and correct them automatically. For example, these days most vandalism is fixed by Wikipedia's robots, or our content editors, who are watching your every move. Be careful.
Unlike paper encyclopedias which can only display a single version of an article, Wikipedia tracks every edit to every page. Each of these versions of the article, or revisions, is listed chronologically in the history tab, from which any and all previous revisions can be viewed. This is useful not only as a historical record by which we can analyze how articles change over time, but also to protect the integrity of the article. Because the most accurate and complete version of an article is always stored and readily accessible, bad edits (whether blatant vandalism or good faith errors) can be quickly reverted.
Special:RecentChanges lists, by default, the 50 most recent changes to all of Wikipedia. Members of Wikipedia:Recent changes patrol periodically scan this page for unusual activity, such as a large removal of content, an automatic edit summary, or even just edits made anonymously. The corresponding diffs can then be examined to determine whether or not the edits were constructive. The 50 most recent edits may have all occurred within the past one to two minutes. Thus, the recent changes patrol ensures that obvious vandalism is reverted within a few minutes of being added.
A watchlist is a MediaWiki feature that presents in a special list format all the recent edits (configurable to display edits up to 30 days old) for every article on the watchlist. On Wikipedia, there are two types of watchlist that are commonly used...
The MediaWiki software upon which Wikipedia is hosted includes a powerful feature called "My watchlist", accessible at the top of the screen by every user who has a Wikipedia account (which are free, by the way). Editors interested in working on or monitoring specific pages can watch those pages. The watchlist simultaneously displays the most recent revisions of every article that an editor is watching. This makes it very easy for an editor to quickly check over the articles they are working on to see if any dubious edits have occurred. Watchlisting insures that editors with a good understanding of an article are aware of any incorrect information added, and that vandalism can be quickly reverted. Using this tool, experienced editors can effectively watch as many as 8,000 pages each.
In general, Wikipedia has a rapid response to notable recent events, to add or update information quickly. Consequently, many other encyclopedias cannot generate the detail content about recent topics as quickly. However, from day to day, some questionable statements can get added into older articles, and it might take a few hours (or days) before that text is removed. An edit-approval process known as "pending changes" has been used in some articles, as a gatekeeper to deter improper additions to articles. The German Wikipedia has used that process to screen pending-change requests for years, and some trusted editors are allowed to approve and release their own proposed updates to articles.
For technical subjects, unusual claims in articles typically take longer to verify or correct, depending on review time needed by experts in the subject. Computer science professor Randy Pausch (1960–2008) reported in his book The Last Lecture about his experience writing an article for the World Book Encyclopedia, and recounted:
He then stated,
However, every article in Wikipedia, even on the most obscure topics, is subject to review, helped by anyone who can read sources about the topic. Highly experienced experts from many fields have written, reviewed, or updated articles, so the technical contents can be extremely detailed, such as in medical articles, or those about physics, computer science, or mathematics.
Wikipedia has a logistical advantage, with thousands of readers to comment or update articles, as a means to quickly detect problems and update articles within hours or minutes, to better reflect the documented sources. Unfortunately, rare bottlenecks have occurred, obstructing progress, when several users repeatedly block attempts by other editors to insert broader, or more recent text, into articles. However, the danger of a sole "senior editor", at another encyclopedia, to clamp down on article content is reduced.
The greater danger is when a group of fervent editors follow a misguided plan to force incorrect text into articles, and that situation requires longer to mediate. A common source of conflict is from slanted text fostered by tabloid journalism which enters wrong ideas into mainstream reports about a topic. Group content disputes have even led to locking an article, then requiring some pre-approved changes to be agreed by hours of prior discussion. Once major sources spread incorrect ideas, it has been extremely difficult to convince others about the actual facts. In some cases, both conflicting views are stated, as being undecided within the expert sources. However, among the nearly 6 million articles, relatively few have been slowed by group disputes.
Note that each other-language Wikpedia has its own procedures for quality control. However, the major-language branches have similar controls, such as to block the editing by known troublemakers, then checking their edit-history contributions to undo any string of improper updates to several articles.