Wikipedia

Wikipedia ( or ) is a collaboratively edited, multilingual, free-access, free content Internet encyclopedia that is supported and hosted by the non-profit Wikimedia Foundation. Volunteers worldwide collaboratively write Wikipedia's 30 million articles in 287 languages, including in the English Wikipedia. Anyone who can access the site can edit almost any of its articles, which on the Internet comprise the largest and most popular general reference work. In February 2014, The New York Times reported that Wikipedia is ranked fifth globally among all websites stating, "With 18 billion page views and nearly 500 million unique visitors a month..., Wikipedia trails just Yahoo, Facebook, Microsoft and Google, the largest with 1.2 billion unique visitors."

Jimmy Wales and Larry Sanger launched Wikipedia on January 15, 2001, the latter creating its name, a portmanteau of wiki (the name of a type of collaborative website, from the Hawaiian word for "quick") and encyclopedia.

Wikipedia's departure from the expert-driven style of encyclopedia-building and the presence of much unacademic content have received extensive attention in print media. In 2006, Time magazine recognized Wikipedia's participation in the rapid growth of online collaboration and interaction by millions of people around the world, in addition to YouTube, reddit, MySpace, and Facebook. Wikipedia has also become known as a news source because of the rapid update of articles related to breaking news.

The open nature of Wikipedia has led to various concerns, such as the quality of writing, vandalism and the accuracy of information. Some articles contain unverified or inconsistent information, though a 2005 investigation in Nature showed that the 42 science articles they compared came close to the level of accuracy of Encyclopædia Britannica and had a similar rate of "serious errors". Britannica replied that the study's methodology and conclusions were flawed. With Wikipedia approaching five million edited articles in 2014, the last edition of Britannica contained approximately forty thousand articles by comparison, which is over one hundred times smaller than the current number of articles edited on Wikipedia. The policies of Wikipedia combine and a.

Editing
Unlike traditional encyclopedias, Wikipedia allows outside editing: except in particularly sensitive and/or vandalism-prone pages that are "protected" to some degree, even without an account readers can edit text without permission. Different language editions modify this policy to some extent; for example, only registered users may create a new article in the English edition. No article is considered to be owned by its creator or any other editor, nor is it vetted by any recognized authority. Instead, editors are supposed to agree on the content and structure of articles by.

By default, an edit to an article immediately becomes available. Articles therefore may contain inaccuracies, ideological biases, or even patent nonsense until or unless another editor corrects them. Different language editions, each under separate administrative control, are free to modify this policy. For example, the German Wikipedia maintains "stable versions" of articles, which have passed certain reviews. Following the protracted trials and community discussion, the "pending changes" system was introduced to English Wikipedia in December 2012. Under this system, new users' edits to certain controversial or vandalism-prone articles would be "subject to review from an established Wikipedia editor before publication".

The software that powers Wikipedia can aid contributors. The "History" page of each article records revisions (though a revision with libelous content, criminal threats, or copyright infringements may be retroactively removed). Editors can use this page to undo undesirable changes or restore lost content. The "Talk" pages associated with article as well as talk pages that are specific to particular contributors help coordinate work among multiple editors. Importantly, editors may use the "Talk" page to reach consensus, sometimes through the use of polling.

Editors can view the website's most "recent changes", which are displayed in reverse chronology. Regular contributors often maintain a "watchlist" of articles that interest them so as to easily track recent changes thereto. In language editions with many articles, editors tend to prefer the "watchlist" because edits have become too many to follow in "recent changes". New page patrol is a process whereby newly created articles are checked for obvious problems. A frequently vandalized article can be semi-protected, allowing only well established users to edit it. A particularly contentious article may be locked so that only administrators are able to make changes.

Computer programs called bots have been used widely to perform simple and repetitive tasks, such as correcting common misspellings and stylistic issues, or to start articles such as geography entries in a standard format from statistical data. There are also some bots designed to warn users making "undesirable" edits, prevent the creation of links to particular websites, and block edits from particular accounts or IP address ranges. Bots on Wikipedia must be approved by administration prior to activation.

Organization of article pages
Articles in Wikipedia are loosely organized according to their and. A new article often starts as a "stub", a very short page consisting of definitions and some links. On the other extreme, the most developed articles may be nominated for "featured article" status. One "featured article" per day, as selected by editors, appears on the main page of Wikipedia. Researcher Giacomo Poderi found that articles tend to reach featured status via the intensive work of a few editors. A 2010 study found unevenness in quality among featured articles and concluded that the community process is ineffective in assessing the quality of articles. In 2007, in preparation for producing a print version, the English-language Wikipedia introduced an assessment scale against which the quality of articles is judged.

A group of Wikipedia editors may form a WikiProject to focus their work on a specific topic area, using its associated discussion page to coordinate changes across multiple articles.

Vandalism
Any edit that changes content in a way that deliberately compromises the integrity of Wikipedia is considered vandalism. The most common and obvious types of vandalism include insertion of obscenities and crude humor. Vandalism can also include advertising language, and other types of spam. Sometimes editors commit vandalism by removing information or entirely blanking a given page. Less common types of vandalism, such as the deliberate addition of plausible but false information to an article, can be more difficult to detect. Vandals can introduce irrelevant formatting, modify page semantics such as the page's title or categorization, manipulate the underlying code of an article, or utilize images disruptively.

Obvious vandalism is generally easy to remove from wiki articles; in practice, the median time to detect and fix vandalism is a few minutes. However, in one high-profile incident in 2005, false information was introduced into the biography of American political figure John Seigenthaler and remained undetected for four months. He was falsely accused of being a suspect in the assassination of John F. Kennedy by an anonymous user, but was actually an administrative assistant to President Kennedy. Seigenthaler, the founding editorial director of USA Today and founder of the Freedom Forum First Amendment Center at Vanderbilt University, called Wikipedia co-founder Wales and asked whether he had any way of knowing who contributed the misinformation. Wales replied that he did not, although the perpetrator was eventually traced. This incident led to policy changes on the site, specifically targeted at tightening up the verifiability of all.

Rules and laws governing content and editor behavior
Content in Wikipedia is subject to the laws (in particular, the copyright laws) of the United States and of the US state of Virginia, where the majority of Wikipedia's servers are located. Beyond legal matters, the editorial principles of Wikipedia are embodied in the, and numerous that are intended to shape the content appropriately. Even these rules are stored in wiki form, and Wikipedia editors as a community write and revise the website's policies and guidelines. Editors can by deleting or modifying non-compliant material. Originally, rules on the non-English editions of Wikipedia were based on a translation of the rules on the English Wikipedia. They have since diverged to some extent.

Content policies
According to the rules on the English Wikipedia, each entry in Wikipedia, to be worthy of inclusion, must be about a topic that is encyclopedic and is not a dictionary entry or dictionary-like. A topic should also meet Wikipedia's standards of "notability", which usually means that it must have received significant coverage in reliable secondary sources such as mainstream media or major academic journals that are independent of the subject of the topic. Further, Wikipedia intends to convey only knowledge that is already established and recognized. It must not present new information or original research. A claim that is likely to be challenged requires a reference to a reliable source. Among Wikipedia editors, this is often phrased as "verifiability, not truth" to express the idea that the readers, not the encyclopedia, are ultimately responsible for checking the truthfulness of the articles and making their own interpretations. This can lead to the removal of information that is valid, thus hindering inclusion of knowledge and growth of the encyclopedia. Finally, Wikipedia must not take sides. All opinions and viewpoints, if attributable to external sources, must enjoy an appropriate share of coverage within an article. This is known as neutral point of view (NPOV).

Dispute resolution and Arbitration Committee
Wikipedia has many methods of settling disputes. A "BOLD, revert, discuss" cycle sometimes occurs, in which an editor changes something, another editor reverts the change, and then the two editors discuss the issue on a talk page. When editors disregard this process – when a change is repeatedly done by one editor and then undone by another – an "edit war" may be asserted to have begun. In order to gain a broader community consensus, editors can raise issues at the Village Pump, or initiate a Request for Comment. Specialized forums exist for centralizing discussion on specific decisions, such as whether or not an article should be deleted. (cf. Notability in English Wikipedia.)

The Arbitration Committee presides over the ultimate dispute resolution method. Although disputes usually arise from a disagreement between two opposing views on how articles should read, the Arbitration Committee explicitly refuses to directly rule on which view should be adopted. Statistical analyses suggest that the committee ignores the content of disputes and focuses on the way disputes are conducted instead, functioning not so much to resolve disputes and make peace between conflicting editors, but to weed out problematic editors while allowing potentially productive editors back in to participate. Therefore, the committee does not dictate the content of articles, although it sometimes condemns content changes when it deems the new content violates Wikipedia policies (for example, if the new content is biased). Its remedies include cautions and probations (used in 63.2% of cases) and banning editors from articles (43.3%), subject matters (23.4%) or Wikipedia (15.7%). Complete bans from Wikipedia are largely limited to instances of impersonation and anti-social behavior. When conduct is not impersonation or anti-social, but rather anti-consensus or violating editing policies, warnings tend to be issued.

Community


Wikipedia's community has been described as cult-like, although not always with entirely negative connotations, and criticized for failing to accommodate inexperienced users. The project's preference for cohesiveness, even if it requires compromise that includes disregard of credentials, has been referred to as "anti-elitism".

Editors in good standing in the community can run for one of many levels of volunteer stewardship: this begins with "administrator", a group of privileged users who have the ability to delete pages, lock articles from being changed in case of vandalism or editorial disputes, and block users from editing. Despite the name, administrators are not supposed to enjoy any special privilege in decision-making; instead, their powers are mostly limited to making edits that have project-wide effects and thus are disallowed to ordinary editors, and to block users making disruptive edits (such as vandalism). As the process of vetting potential Wikipedia administrators has become more rigorous, fewer editors are promoted to admin status than in years past.

Contributors


Wikipedia does not require that its editors provide identification. However, as Wikipedia grew, "Who writes Wikipedia?" became one of the questions frequently asked on the project, often with a reference to other Web 2.0 projects such as Digg. Wales once argued that only "a community ... a dedicated group of a few hundred volunteers" makes the bulk of contributions to Wikipedia and that the project is therefore "much like any traditional organization". Wales performed a study finding that over 50% of all the edits were done by just 0.7% of the users (at the time: 524 people). This method of evaluating contributions was later disputed by Aaron Swartz, who noted that several articles he sampled had large portions of their content (measured by number of characters) contributed by users with low edit counts. A study performed in 2012 Wikipedia had about 80,000 active users with about 30,000 being the top 2%-10%. Up to 60% of Wikipedia's registered users never make another edit after their first 24 hours. Possible explanations are that such users register for only a single purpose, or are scared away by their experiences. Goldman writes that editors who fail to comply with Wikipedia cultural rituals, such as signing talk pages, implicitly signal that they are Wikipedia outsiders, increasing the odds that Wikipedia insiders will target their contributions as a threat. Becoming a Wikipedia insider involves non-trivial costs: the contributor is expected to build a user page, learn Wikipedia-specific technological codes, submit to an arcane dispute resolution process, and learn a "baffling culture rich with in-jokes and insider references". Non-logged-in users are in some sense second-class citizens on Wikipedia, as "participants are accredited by members of the wiki community, who have a vested interest in preserving the quality of the work product, on the basis of their ongoing participation", but the contribution histories of IP addresses cannot necessarily with any certainty be credited to, or blamed upon, a particular user.

A 2007 study by researchers from Dartmouth College found that "anonymous and infrequent contributors to Wikipedia […] are as reliable a source of knowledge as those contributors who register with the site". A 2009 study by Business Insider editor and journalist Henry Blodget showed that in a random sample of articles most content in Wikipedia (measured by the amount of contributed text that survives to the latest sampled edit) is created by "outsiders" (users with low edit counts), while most editing and formatting is done by "insiders" (a select group of established users). A 2008 study found that Wikipedians were less agreeable, open, and conscientious than others. A 2009 study suggested there was "evidence of growing resistance from the Wikipedia community to new content".

One study found that the contributor base to Wikipedia "was barely 13% women; the average age of a contributor was in the mid-20s". A 2011 study by researchers from the University of Minnesota found that females comprised 16.1% of the 38,497 editors who started editing Wikipedia during 2009. In a January 2011 New York Times article, Noam Cohen observed that just 13% of Wikipedia's contributors are female according to a 2009 Wikimedia Foundation survey. Sue Gardner, a former executive director of the Wikimedia Foundation, hopes to see female contributions increase to twenty-five percent by 2015. Linda Basch, president of the National Council for Research on Women, noted the contrast in these Wikipedia editor statistics with the percentage of women currently completing bachelor's degrees, master's degrees and PhD programs in the United States (all at rates of 50 percent or greater).

In response, various universities have hosted edit-a-thons to encourage more woman to participate in the Wikipedia community. In fall 2013, 15 colleges and universities, including Yale, Brown, and Pennsylvania State, offered college credit for students to "write feminist thinking" into Wikipedia about technology. However, few women continued as active members of Wikipedia after the edit-a-thons were over. When asked why, the most common response was that they were, "too busy".

Open collaboration
In 2003, economics PhD student Andrea Ciffolilli argued that the low transaction costs of participating in wiki software create a catalyst for collaborative development, and that such features as easy access to past versions of a page favor "creative construction" over "creative destruction". In his 2008 book, The Future of the Internet and How to Stop It, Zittrain cites Wikipedia's success as a case study in how open collaboration has fostered innovation on the web.

At OOPSLA 2009, Wikimedia chief technology officer and senior software architect Brion Vibber gave a presentation entitled "Community Performance Optimization: Making Your People Run as Smoothly as Your Site" in which he discussed the challenges of handling the contributions from a large community and compared the process to that of software development.



The Wikipedia Signpost is the community newspaper on the English Wikipedia, and was founded by Michael Snow, an administrator and the former chair of the Wikimedia Foundation board of trustees. It covers news and events from the site, as well as major events from other Wikimedia projects, such as Wikimedia Commons.

Wikipedians sometimes award one another barnstars for good work in order to appreciate a wide range of valued work extending far beyond simple editing to include social support, administrative actions, and types of articulation work. The barnstar phenomenon has been analyzed to determine what implications it might have for other communities engaged in large-scale collaborations.

Language editions
There are currently 287 language editions (or language versions) of Wikipedia; of these, eleven have over one million articles each (English, Dutch, German, French, Italian, Polish, Spanish, Russian, Swedish, Vietnamese, and Waray-Waray), four more have over 700,000 articles (Cebuano, Chinese, Japanese, Portuguese), 37 more have over 100,000 articles, and 73 more have over 10,000 articles. The largest, the English Wikipedia, has over million articles. , according to Alexa, the English subdomain (en.wikipedia.org; English Wikipedia) receives approximately 56% of Wikipedia's cumulative traffic, with the remaining split among the other languages (Spanish: 9%; Japanese: 8%; Russian: 6%; German: 5%; French: 4%; Italian: 3%). As of December 2013, the six largest language editions are (in order of article count) the English, Dutch, German, Swedish, French, and Italian Wikipedias. The coexistence of multilingual content on Wikipedia is made possible by Unicode, whose support was first introduced into Wikipedia in January 2002 by Brion Vibber after he had similarly implemented the alphabet of Esperanto.

Since Wikipedia is based on the Web and therefore worldwide, contributors of a same language edition may use different dialects or may come from different countries (as is the case for the English edition). These differences may lead to some conflicts over spelling differences (e.g. colour versus color) or points of view.

Though the various language editions are held to global policies such as "neutral point of view", they diverge on some points of policy and practice, most notably on whether images that are not licensed freely may be used under a claim of fair use.

Jimmy Wales has described Wikipedia as "an effort to create and distribute a free encyclopedia of the highest possible quality to every single person on the planet in their own language". Though each language edition functions more or less independently, some efforts are made to supervise them all. They are coordinated in part by Meta-Wiki, the Wikimedia Foundation's wiki devoted to maintaining all of its projects (Wikipedia and others). For instance, Meta-Wiki provides important statistics on all language editions of Wikipedia, and it maintains a list of articles every Wikipedia should have. The list concerns basic content by subject: biography, history, geography, society, culture, science, technology, and mathematics. As for the rest, it is not rare for articles strongly related to a particular language not to have counterparts in another edition. For example, articles about small towns in the United States might only be available in English, even when they meet notability criteria of other language Wikipedia projects.



Translated articles represent only a small portion of articles in most editions, in part because fully automated translation of articles is disallowed. Articles available in more than one language may offer "interwiki links", which link to the counterpart articles in other editions.

A research article published in PLoS ONE in 2012, using the circadian patterns of editorial activities of the community, estimated the share of contributions to different editions of Wikipedia from different regions of the world. For instance, it has been reported that edits from North America are limited to almost 50% in the English Wikipedia and this value decreases to twenty-five percent in simple English Wikipedia. The article also covers some other editions in different languages. The Wikimedia Foundation hopes to increase the number of editors in the Global South to thirty-seven percent by 2015.

On 1 March 2014, The Economist in an article titled "The Future of Wikipedia" cited a trend analysis concerning data published by Wikimedia stating that: "The number of editors for the English-language version has fallen by a third in seven years." The attrition rate for active editors in English Wikipedia was cited by The Economist as substantially in contrast to statistics for Wikipedia in other languages (non-English Wikipedia). The Economist reported that the number of contributors with an average of five of more edits per month was relatively constant since 2008 for Wikipedia in other languages at approximately 42,000 editors within narrow seasonal variances of about 2,000 editors up or down. The attrition rates for editors in English Wikipedia, by sharp comparison, were cited as peaking in 2007 at approximately 50,000 editors which has dropped to 30,000 editors as of the start of 2014. At the quoted trend rate, the number of active editors in English Wikipedia has lost approximately 20,000 editors to attrition since 2007, and the documented trend rate indicates the loss of another 20,000 editors by 2021, down to 10,000 active editors on English Wikipedia by 2021 if left unabated. Given that the trend analysis published in The Economist presents the number of active editors for Wikipedia in other languages (non-English Wikipedia) as remaining relatively constant and successful in sustaining its numbers at approximately 42,000 active editors, the contrast has pointed to the effectiveness of Wikipedia in other languages to retain its active editors on a renewable and sustained basis. No comment was made concerning which of the differentiated edit policy standards from Wikipedia in other languages (non-English Wikipedia) would provide a possible alternative to English Wikipedia for effectively ameliorating substantial editor attrition rates on the English language Wikipedia.

History


Wikipedia began as a complementary project for Nupedia, a free online English-language encyclopedia project whose articles were written by experts and reviewed under a formal process. Nupedia was founded on March 9, 2000, under the ownership of Bomis, a web portal company. Its main figures were the Bomis CEO Jimmy Wales and Larry Sanger, editor-in-chief for Nupedia and later Wikipedia. Nupedia was licensed initially under its own Nupedia Open Content License, switching to the GNU Free Documentation License before Wikipedia's founding at the urging of Richard Stallman. Sanger and Wales founded Wikipedia. While Wales is credited with defining the goal of making a publicly editable encyclopedia, Sanger is credited with the strategy of using a wiki to reach that goal. On January 10, 2001, Sanger proposed on the Nupedia mailing list to create a wiki as a "feeder" project for Nupedia.

Wikipedia was formally launched on January 15, 2001, as a single English-language edition at www.wikipedia.com, and announced by Sanger on the Nupedia mailing list. Wikipedia's policy of "neutral point-of-view" was codified in its first months. Otherwise, there were relatively few rules initially and Wikipedia operated independently of Nupedia. Originally, Bomis intended to make Wikipedia a business for profit.

Wikipedia gained early contributors from Nupedia, Slashdot postings, and web search engine indexing. On August 8, 2001, Wikipedia had over 8,000 articles. On September 25, 2001, Wikipedia had over 13,000 articles. And by the end of 2001 it had grown to approximately 20,000 articles and 18 language editions. It had reached 26 language editions by late 2002, 46 by the end of 2003, and 161 by the final days of 2004. Nupedia and Wikipedia coexisted until the former's servers were taken down permanently in 2003, and its text was incorporated into Wikipedia. English Wikipedia passed the mark of two million articles on September 9, 2007, making it the largest encyclopedia ever assembled, surpassing even the 1407 Yongle Encyclopedia, which had held the record for 600 years.

Citing fears of commercial advertising and lack of control in Wikipedia, users of the Spanish Wikipedia forked from Wikipedia to create the Enciclopedia Libre in February 2002. These moves encouraged Wales to announce that Wikipedia would not display advertisements, and to change Wikipedia's domain from wikipedia.com to wikipedia.org.

Though the English Wikipedia reached three million articles in August 2009, the growth of the edition, in terms of the numbers of articles and of contributors, appears to have peaked around early 2007. Around 1,800 articles were added daily to the encyclopedia in 2006; by 2013 that average was roughly 800. A team at the Palo Alto Research Center attributed this slowing of growth to the project's increasing exclusivity and resistance to change. Others suggest that the growth is flattening naturally because articles that could be called "low-hanging fruit" – topics that clearly merit an article – have already been created and built up extensively.

In November 2009, a researcher at the Rey Juan Carlos University in Madrid (Spain) found that the English Wikipedia had lost 49,000 editors during the first three months of 2009; in comparison, the project lost only 4,900 editors during the same period in 2008. The Wall Street Journal cited the array of rules applied to editing and disputes related to such content among the reasons for this trend. Wales disputed these claims in 2009, denying the decline and questioning the methodology of the study. Two years later, Wales acknowledged the presence of a slight decline, noting a decrease from "a little more than 36,000 writers" in June 2010 to 35,800 in June 2011. In the same interview, Wales also claimed the number of editors was "stable and sustainable," a claim which was questioned by MIT's Technology Review in a 2013 article titled "The Decline of Wikipedia." In July 2012, the Atlantic reported that the number of administrators is also in decline. In the 25 November 2013 issue of New York magazine, Katherine Ward stated "Wikipedia, the sixth-most-used website, is facing an internal crisis. In 2013, MIT's Technology Review revealed that since 2007, the site has lost a third of the volunteer editors who update and correct the online encyclopedia's millions of pages and those still there have focused increasingly on minutiae."



In January 2007, Wikipedia entered for the first time the top-ten list of the most popular websites in the United States, according to comScore Networks. With 42.9 million unique visitors, Wikipedia was ranked number 9, surpassing the New York Times (#10) and Apple (#11). This marked a significant increase over January 2006, when the rank was number 33, with Wikipedia receiving around 18.3 million unique visitors. As of the start of February 2014, Wikipedia was the sixth most popular website worldwide according to Alexa Internet, receiving more than 2.7 billion US pageviews every month, out of a global monthly total of over 12 billion pageviews. On 9 February 2014, The New York Times reported that Wikipedia is ranked fifth globally among all websites, "according to the ratings firm comScore."

On January 18, 2012, the English Wikipedia participated in a series of coordinated protests against two proposed laws in the United States Congress—the Stop Online Piracy Act (SOPA) and the PROTECT IP Act (PIPA)—by blacking out its pages for 24 hours. More than 162 million people viewed the blackout explanation page that temporarily replaced Wikipedia content.

Loveland and Reagle argue that, in process, Wikipedia follows a long tradition of historical encyclopedias that accumulated improvements piecemeal through "stigmergic accumulation".

On 20 January 2014, Subodh Varma reporting for The Economic Times indicated that not only had Wikipedia growth flattened but that it has "lost nearly 10 per cent of its page-views last year. That's a decline of about 2 billion between December 2012 and December 2013. Its most popular versions are leading the slide: page-views of the English Wikipedia declined by 12 per cent, those of German version slid by 17 per cent and the Japanese version lost 9 per cent." Varma added that, "While Wikipedia's managers think that this could be due to errors in counting, other experts feel that Google's Knowledge Graphs project launched last year may be gobbling up Wikipedia users." When contacted on this matter, Clay Shirky, associate professor at New York University and fellow at Harvard's Berkman Center for internet and Security indicated that he suspected much of the page-view decline was due to Knowledge Graphs, stating, "If you can get your question answered from the search page, you don't need to click [any further]."

Analysis of content
Although poorly written articles are flagged for improvement, critics note that the style and quality of individual articles may vary greatly. Others argue that inherent biases (willful or not) arise in the presentation of facts, especially controversial topics and public or historical figures. Although Wikipedia's stated mission is to provide information and not argue value judgements, articles often contain overly specialized, trivial, or objectionable material.

In 2006, the Wikipedia Watch criticism website listed dozens of examples of plagiarism by Wikipedia editors on the English version.

Accuracy of content
Articles for traditional encyclopedias such as Encyclopædia Britannica are carefully and deliberately written by experts, lending such encyclopedias a reputation for accuracy. Conversely, Wikipedia is often cited for factual inaccuracies and misrepresentations. However, a peer review in 2005 of forty-two scientific entries on both Wikipedia and Encyclopedia Britannica by the science journal Nature found few differences in accuracy, and concluded that 'the average science entry in Wikipedia contained around four inaccuracies; Britannica, about three.' Reagle suggested that while the study reflects "a topical strength of Wikipedia contributors" in science articles, "Wikipedia may not have fared so well using a random sampling of articles or on humanities subjects." The findings by Nature were disputed by Encyclopædia Britannica, and in response, Nature gave a rebuttal of the points raised by Britannica.

As a consequence of the open structure, Wikipedia "makes no guarantee of validity" of its content, since no one is ultimately responsible for any claims appearing in it. Concerns have been raised by PC World in 2009 regarding the lack of accountability that results from users' anonymity, the insertion of false information, vandalism, and similar problems.

Economist Tyler Cowen wrote: "If I had to guess whether Wikipedia or the median refereed journal article on economics was more likely to be true, after a not so long think I would opt for Wikipedia." He comments that some traditional sources of non-fiction suffer from systemic biases and novel results, in his opinion, are over-reported in journal articles and relevant information is omitted from news reports. However, he also cautions that errors are frequently found on Internet sites, and that academics and experts must be vigilant in correcting them.

Critics argue that Wikipedia's open nature and a lack of proper sources for most of the information makes it unreliable. Some commentators suggest that Wikipedia may be reliable, but that the reliability of any given article is not clear. Editors of traditional reference works such as the Encyclopædia Britannica have questioned the project's utility and status as an encyclopedia.

Wikipedia's open structure inherently makes it an easy target for Internet trolls, spammers, and those with an agenda to push. The addition of political spin to articles by organizations including members of the US House of Representatives and special interest groups has been noted, and organizations such as Microsoft have offered financial incentives to work on certain articles. For example, in August 2007, the website WikiScanner began to trace the sources of changes made to Wikipedia by anonymous editors without Wikipedia accounts. The program revealed that many such edits were made by corporations or government agencies changing the content of articles related to them, their personnel or their work. These issues have been parodied, notably by Stephen Colbert on The Colbert Report.

Quality of writing
Because contributors usually rewrite small portions of an entry rather than making full-length revisions, high- and low-quality content may be intermingled within an entry. Roy Rosenzweig, a history professor, stated that American National Biography Online outperformed Wikipedia in terms of its "clear and engaging prose", which, he said, was an important aspect of good historical writing. Contrasting Wikipedia's treatment of Abraham Lincoln to that of Civil War historian James McPherson in American National Biography Online, he said that both were essentially accurate and covered the major episodes in Lincoln's life, but praised "McPherson's richer contextualization […] his artful use of quotations to capture Lincoln's voice […] and […] his ability to convey a profound message in a handful of words." By contrast, he gives an example of Wikipedia's prose that he finds "both verbose and dull". Rosenzweig also criticized the "waffling—encouraged by the npov policy—[which] means that it is hard to discern any overall interpretive stance in Wikipedia history". By example, he quoted the conclusion of Wikipedia's article on William Clarke Quantrill. While generally praising the article, he pointed out its "waffling" conclusion: "Some historians […] remember him as an opportunistic, bloodthirsty outlaw, while others continue to view him as a daring soldier and local folk hero."

Other critics have made similar charges that, even if Wikipedia articles are factually accurate, they are often written in a poor, almost unreadable style. Frequent Wikipedia critic Andrew Orlowski commented: "Even when a Wikipedia entry is 100 per cent factually correct, and those facts have been carefully chosen, it all too often reads as if it has been translated from one language to another then into to a third, passing an illiterate translator at each stage." A study of articles on cancer was undertaken in 2010 by Yaacov Lawrence of the Kimmel Cancer Center at Thomas Jefferson University limited to those Wikipedia articles which could be found in the Physician Data Query and excluding Wikipedia articles written at the "start" class or the "stub" class level. Lawrence found the articles accurate but not very readable, and thought that "Wikipedia's lack of readability (to non-college readers) may reflect its varied origins and haphazard editing". The Economist argued that better-written articles tend to be more reliable: "inelegant or ranting prose usually reflects muddled thoughts and incomplete information".

On 5 March 2014, Julie Beck writing for The Atlantic magazine in an article titled "Doctors’ #1 Source for Healthcare Information: Wikipedia", stated that "Fifty percent of physicians look up conditions on the (Wikipedia) site, and some are editing articles themselves to improve the quality of available information." Beck continued to detail in this article new programs of Dr. Amin Azzam at the University of San Francisco to offer medical school courses to medical students for learning to edit and improve Wikipedia articles on health-related issues, as well as internal quality control programs within Wikipedia organized by Dr. James Heilman to improve a group of 200 health-related articles of central medical importance up to Wikipedia's highest standard of peer review evaluated articles using its Featured Article and Good Article peer review evaluation standards. In a 7 May 2014 follow-up article in The Atlantic titled "Can Wikipedia Ever Be a Definitive Medical Text", Julie Beck quotes Wikiproject's Dr. James Heilman as stating: "Just because a reference is peer-reviewed doesn't mean it's a high-quality reference." Beck added that: "Wikipedia has its own peer review process before articles can be classified as 'good' or 'featured.' Heilman, who has participated in that process before, says 'less than 1 percent' of Wikipedia's medical articles have passed.

Coverage of topics and systemic bias
Wikipedia seeks to create a summary of all human knowledge in the form of an online encyclopedia, with each topic covered encyclopedically in one article. Since it has terabytes of disk space, it can have far more topics than can be covered by any printed encyclopedia. The exact degree and manner of coverage on Wikipedia is under constant review by its editors, and disagreements are not uncommon (see deletionism and inclusionism). Wikipedia contains materials that some people may find objectionable, offensive, or pornographic because Wikipedia is not censored. The policy has sometimes proved controversial: in 2008, Wikipedia rejected an online petition against the inclusion of images of Muhammad in the English edition of its Muhammad article, citing this policy. The presence of politically, religiously, and pornographically sensitive materials in Wikipedia has led to the censorship of Wikipedia by national authorities in China, Pakistan, and the United Kingdom, among other countries.

A 2008 study conducted by researchers at Carnegie Mellon University and Palo Alto Research Center gave a distribution of topics as well as growth (from July 2006 to January 2008) in each field:


 * Culture and the arts: 30% (210%)
 * Biographies and persons: 15% (97%)
 * Geography and places: 14% (52%)
 * Society and social sciences: 12% (83%)
 * History and events: 11% (143%)
 * Natural and physical sciences: 9% (213%)
 * Technology and the applied sciences: 4% (−6%)
 * Religions and belief systems: 2% (38%)
 * Health: 2% (42%)
 * Mathematics and logic: 1% (146%)
 * Thought and philosophy: 1% (160%)

These numbers refer only to the quantity of articles: it is possible for one topic to contain a large number of short articles and another to contain a small number of large ones. Through its "Wikipedia Loves Libraries" program, Wikipedia has partnered with major public libraries such as the New York Public Library for the Performing Arts to expand its coverage of underrepresented subjects and articles.

A 2011 study conducted by researchers at the University of Minnesota indicated that male and female editors focus on different coverage topics. There was a greater concentration of females in the People and Arts category, while males focus more on Geography and Science.

Coverage of topics and selectional bias
In September 2009, Wikipedia articles covered about half a million places on Earth. However, research conducted by the Oxford Internet Institute has shown that the geographic distribution of articles is highly uneven. Most articles are written about North America, Europe, and East Asia, with very little coverage of large parts of the developing world, including most of Africa.

A "selection bias" may arise when more words per article are devoted to one public figure than a rival public figure. Editors may dispute suspected biases and discuss controversial articles, sometimes at great length. Wales has noted the dangers of bias on controversial political topics or polarizing public figures.

Systemic bias
When multiple editors contribute to one topic or set of topics, there may arise a systemic bias, such as non-opposite definitions for apparent antonyms. In 2011 Wales noted that the unevenness of coverage is a reflection of the demography of the editors, which predominantly consists of young males with high education levels in the developed world ( previously). The 22 October 2013 essay by Tom Simonite in MIT's Technology Review titled "The Decline of Wikipedia" discussed the effect of systemic bias and policy creep on recent downward trends in the number of editors available to support Wikipedia's range and coverage of topics.

Systemic bias on Wikipedia may follow that of culture generally, for example favouring certain ethnicities or majority religions. It may more specifically follow the biases of Internet culture, inclining to being young, male, English-speaking, educated, technologically aware, and wealthy enough to spare time for editing. Biases of its own may include over-emphasis on topics such as pop culture, technology, and current events.

The study of systemic bias is part of the field titled organizational behavior in industrial organization economics. It is studied in several principle modalities in both non-profit and for-profit institutions. The issue of concern is that patterns of behavior may develop within large institutions, such as Wikipedia, which become institutionally maladapted and harmful to the productivity and viability of the larger institutions from which they develop. The eight major categories of study for maladaptive organizational behavior as they apply to maintaining and supporting Wikipedia are: (1) Counterproductive work behavior or CWB consists of behavior by employees or volunteer editors that harm or intended to harm Wikipedia and its editors constructive contributions usually identified as "edit warring" or "disruptive editing"; (2) Mistreatment of human resources used for editing and maintaining Wikipedia; There are several types of mistreatment that employees or volunteer editors for Wikipedia endure while editing along with a large contingent of corrective measures and norms of editing policy available as counter-measures for such mistreatment; (3) Abusive supervision is the extent to which a supervisor engages in a pattern of behavior that harms subordinates, such as fellow editors at Wikipedia. Editors at various levels of experience are often entrusted with corrective procedures and referrals for correcting abusive editing practices when these are identified.; (4) Bullying; Although definitions of bullying vary, it involves a repeated pattern of harmful behaviors directed towards individuals, such as editors viewed as individual contributors.; (5) Incivility consists of low-intensity discourteous and rude behavior with ambiguous intent to detract from productivity and violate norms for appropriate behavior in the workplace, such as that which may be found while editing contributions.; (6) Gender bias is behavior that denigrates or mistreats an individual worker, such as a voluntary editor at Wikipedia, due to his or her gender, creates an offensive workplace for the worker and interferes with an individual being able to do the job; The gender gap at Wikipedia is well-recognized as an issue deserving of attention as discussed in the separate subsection above; Although an effective counter-measure to this gender gap has yet to be fully identified at Wikipedia, several programs have been examined for their possible potential in moving towards achieving gender equality.; (7) Occupational stress concerns the imbalance between the demands (aspects of occupation or, for example, Wikipedia editing that require mental or physical effort) and resources that help cope with demands.; and (8) Maladaptive standards and practices, where the accumulation of piecemeal standards adopted over time begin to show a cumulative negative effect upon the overall success and improvement of the institutions they were originally designed to guide and assist.

In 2013 Deepak Chopra said that "a band of committed skeptics [on Wikipedia] have focused their efforts to discredit anyone whom they judge an enemy". In an interview with BBC World Service, Rupert Sheldrake made similar complaints about a group of skeptics influencing Wikipedia. University of Chicago professor Jerry Coyne responded to the allegation citing evidence that the claim was false, and chided BBC World Service for allowing Sheldrake to "proclaim his conspiracy theories" on the station.

Taha Yasserri of the University of Oxford in 2013 studied the statistical trends of systemic bias introduced by editing conflicts and their resolution on Wikipedia. The research was among the most technical studies of systemic bias related to organizational behavior at Wikipedia examined as the counterproductive work behavior of edit warring. Yasserri contended that simple reverts or "undo" operations were not the most significant measure of counterproductive behavior at Wikipedia and instead relied on the statistical measurement of detecting "reverting/reverted pairs" or "mutually reverting edit pairs." Such a "mutually reverting edit pair" is defined where one editor reverts the edit of another editor who then, in sequence, returns to revert the first editor in the "mutually reverting edit pairs." The results were tabulated for all language versions of Wikipedia, with the English Wikipedia three largest conflict rates being for articles covering (i) G.W. Bush, (ii) Anarchism and (iii) Mohammad. By comparison, for German Wikipedia the three largest conflict rates at the time of the Oxford study were for the articles covering (i) Croatia, (ii) Scientology and (iii) 9/11 Conspiracy Theories.

Citing Wikipedia
Most university lecturers discourage students from citing any encyclopedia in academic work, preferring primary sources; some specifically prohibit Wikipedia citations. Wales stresses that encyclopedias of any type are not usually appropriate to use as citeable sources, and should not be relied upon as authoritative. Wales once said he receives about ten emails weekly from students saying they got failing grades on papers because they cited Wikipedia; he told the students they got what they deserved. "For God's sake, you're in college; don't cite the encyclopedia", he said.

In February 2007, an article in The Harvard Crimson newspaper reported that a few of the professors at Harvard University include Wikipedia in their syllabi, but that there is a split in their perception of using Wikipedia. In June 2007, former president of the American Library Association Michael Gorman condemned Wikipedia, along with Google, stating that academics who endorse the use of Wikipedia are "the intellectual equivalent of a dietitian who recommends a steady diet of Big Macs with everything".

A Harvard law textbook, Legal Research in a Nutshell (2011), cites Wikipedia as a "general source" that "can be a real boon" in "coming up to speed in the law governing a situation" and, "while not authoritative, can provide basic facts as well as leads to more in-depth resources".

Explicit content
Wikipedia has been criticized for allowing information of graphic content. Articles depicting arguably objectionable content (such as Child nudity, Feces, Cadaver, Human penis, and Vulva) contain graphic pictures and detailed information easily available to anyone with access to the internet, including children.

The site also includes sexual content such as images and videos of masturbation and ejaculation, as well as photos from hardcore pornographic films in its articles.

Depictions of child nudity
The Wikipedia article about Virgin Killer – a 1976 album from German heavy metal band Scorpions – features a picture of the album's original cover, which depicts a naked prepubescent girl. The original release cover caused controversy and was replaced in some countries. In December 2008, access to the Wikipedia article Virgin Killer was blocked for four days by most Internet service providers in the United Kingdom, after it was reported by a member of the public as child pornography, to the Internet Watch Foundation (IWF), which issues a stop list to Internet service providers. IWF, a non-profit, non-government-affiliated organization, later criticized the inclusion of the picture as "distasteful".

In April 2010, Sanger wrote a letter to the Federal Bureau of Investigation, outlining his concerns that two categories of images on Wikimedia Commons contained child pornography, and were in violation of US federal obscenity law. Sanger later clarified that the images, which were related to pedophilia and one about lolicon, were not of real children, but said that they constituted "obscene visual representations of the sexual abuse of children", under the PROTECT Act of 2003. That law bans photographic child pornography and cartoon images and drawings of children that are obscene under American law. Sanger also expressed concerns about access to the images on Wikipedia in schools. Wikimedia Foundation spokesman Jay Walsh strongly rejected Sanger's accusation, saying that Wikipedia did not have "material we would deem to be illegal. If we did, we would remove it." Following the complaint by Sanger, Wales deleted sexual images without consulting the community. After some editors who volunteer to maintain the site argued that the decision to delete had been made hastily, Wales voluntarily gave up some of the powers he had held up to that time as part of his co-founder status. He wrote in a message to the Wikimedia Foundation mailing-list that this action was "in the interest of encouraging this discussion to be about real philosophical/content issues, rather than be about me and how quickly I acted". Critics, including Wikipediocracy, noticed that many of the pornographic images deleted from Wikipedia since 2010 have reappeared.

Privacy
One privacy concern in the case of Wikipedia is the right of a private citizen to remain private: to remain a "private citizen" rather than a "public figure" in the eyes of the law. It is a battle between the right to be anonymous in cyberspace and the right to be anonymous in real life ("meatspace"). A particular problem occurs in the case of an individual who is relatively unimportant and for whom there exists a Wikipedia page against her or his wishes.

In January 2006, a German court ordered the German Wikipedia shut down within Germany because it stated the full name of Boris Floricic, aka "Tron", a deceased hacker. On February 9, 2006, the injunction against Wikimedia Deutschland was overturned, with the court rejecting the notion that Tron's right to privacy or that of his parents was being violated.

Wikipedia has a "" that uses the OTRS system to handle queries without having to reveal the identities of the involved parties. This is used, for example, in confirming the permission for using individual images and other media in the project.

Criticism
As Wikipedia has become a main source for a wide range of general knowledge, criticism sites have developed that were instrumental in exposing the dark side of Wikipedia such as paid advocacy. As of 2014, the most prominent site is Wikipediocracy, which, according to Wikipedia, "has provided some journalists with background information on Wikipedia's controversies."

The open nature of Wikipedia has led to various concerns, such as the quality of writing, vandalism and the accuracy of information. Some articles may contain unverified or inconsistent information, against which Wikipedia applies policies for promoting and ensuring a. Other criticisms of Wikipedia, as an online encyclopedia, include claims that the very principle of being open for editing by anyone makes it difficult for Wikipedia to be fully authoritative and reliable (see Reliability of Wikipedia), that it occasionally exhibits systemic bias, and that its group dynamics sometimes hinder its goals were raised in a 2012 article in The Chronicle of Higher Education. The fact that Wikipedia was not principally designed to provide perfectly correct information about a subject, but rather concentrates on consensus viewpoints and the majority “weight” of viewpoints has led The Chronicle of Higher Education and The Journal of Academic Librarianship to assert that sometimes Wikipedia creates articles which occasionally present incomplete or inadequate information. Wikipedia maintains that the use and application of its expanding editing policies provides for many useful safeguards against such occurrences.

Wikimedia Foundation and the Wikimedia chapters


Wikipedia is hosted and funded by the Wikimedia Foundation, a non-profit organization which also operates Wikipedia-related projects such as Wiktionary and Wikibooks. The Wikimedia Foundation relies on public contributions and grants to fund its mission. The Wikimedia chapters, local associations of users and supporters of the Wikimedia projects, also participate in the promotion, development, and funding of the project. The 22 October 2013 essay by Tom Simonite in MIT's Technology Review titled "The Decline of Wikipedia" was accurate in describing Sue Gardner's progress in fund raising while at the foundation. "On Gardner's watch, the funds the Wikimedia Foundation has raised each year to support the site have grown from $4 million to $45 million." The foundation's most recent IRS Form 990 shows revenue of $39.7 million and expenses of almost $29 million, with assets of $37.2 million and liabilities of about $2.3 million.

In May 2014, Wikimedia Foundation named Lila Tretikov as its new Executive Director, who is taking over for Sue Gardner. The Wall Street Journal reported on 1 May 2014 that Tretikov's information technology background from her years at University of California offers Wikipedia an opportunity to develop in more concentrated directions guided by her often repeated position statement that, "Information, like air, wants to be free." The same Wall Street Journal article reported these directions of development according to an interview with spokesman Jay Walsh of Wikimedia who "said Tretikov would address that issue (paid advocacy) as a priority. 'We are really pushing toward more transparency... We are reinforcing that paid advocacy is not welcome.' Initiatives to involve greater diversity of contributors, better mobile support of Wikipedia, new geo-location tools to find local content more easily, and more tools for users in the second and third world are also priorities, Walsh said."

Software operations and support
The operation of Wikipedia depends on MediaWiki, a custom-made, free and open source wiki software platform written in PHP and built upon the MySQL database system. The software incorporates programming features such as a macro language, variables, a transclusion system for templates, and URL redirection. MediaWiki is licensed under the GNU General Public License and it is used by all Wikimedia projects, as well as many other wiki projects. Originally, Wikipedia ran on UseModWiki written in Perl by Clifford Adams (Phase I), which initially required CamelCase for article hyperlinks; the present double bracket style was incorporated later. Starting in January 2002 (Phase II), Wikipedia began running on a PHP wiki engine with a MySQL database; this software was custom-made for Wikipedia by Magnus Manske. The Phase II software was repeatedly modified to accommodate the exponentially increasing demand. In July 2002 (Phase III), Wikipedia shifted to the third-generation software, MediaWiki, originally written by Lee Daniel Crocker.

Several MediaWiki extensions are installed to extend the functionality of the MediaWiki software.

In April 2005, a Lucene extension was added to MediaWiki's built-in search and Wikipedia switched from MySQL to Lucene for searching. The site currently uses Lucene Search 2.1, which is written in Java and based on Lucene library 2.3.

In July 2013, after extensive beta testing, a WYSIWYG (What You See Is What You Get) extension, VisualEditor, was opened to public use. It was met with much rejection and criticism, and was described as "slow and buggy". The feature was turned off afterward.

Internal quality control and assessment of importance
Wikipedia, in general, uses a two axis approach to the internal quality control and assessment of importance which it uses to organize the support and development of its content for users. The range of quality control assessments begin with "Stub" class and "Start" class assessments, which then are refined and improved to "C" class and "B" class, respectively, until the article undergoes community peer review to meet one of the highest community quality standards: either A-Class, "Good Article" or, the highest quality of "Featured Article". Of the total of about 4.4 million articles assessed as of 11 December 2013, approximately five thousand are at the "Featured Article" status (about .1% of total). These statistics are actively updated and maintained by the internal quality control standards at Wikipedia.

The second axis of quality control is the assessment of importance within individual topic-oriented editor communities, called WikiProjects. These Wikiprojects assign article importance based on their relative importance within their topic area. These range across four levels of gradation from "Top" importance, to "High" importance, to "Mid" importance, to "Low" importance. Of the total number of 4.4 million articles supported as of 11 December 2013, approximately 41 thousand are of "Top" importance ranging up to approximately 1.98 million articles assessed internally as of "Low" importance. These statistics are actively updated and maintained by Wikipedia and are cross-correlated with its quality assessments of individual articles as described above.

''[Note that the table above is updated automatically, but the bar-chart and the two pie-charts are not auto-updated. In them, new data has to be entered by a Wikipedia editor (i.e. user). Also, all pie-charts may be displayed properly in desktop view, but not in mobile view.]''

Hardware operations and support
Wikipedia receives between 25,000 and 60,000 page requests per second, depending on time of day. Page requests are first passed to a front-end layer of Squid caching servers. Further statistics, based on a publicly available 3-month Wikipedia access trace, are available. Requests that cannot be served from the Squid cache are sent to load-balancing servers running the Linux Virtual Server software, which in turn pass the request to one of the Apache web servers for page rendering from the database. The web servers deliver pages as requested, performing page rendering for all the language editions of Wikipedia. To increase speed further, rendered pages are cached in a distributed memory cache until invalidated, allowing page rendering to be skipped entirely for most common page accesses.

Wikipedia employed a single server until 2004, when the server setup was expanded into a distributed multitier architecture. In January 2005, the project ran on 39 dedicated servers in Florida. This configuration included a single master database server running MySQL, multiple slave database servers, 21 web servers running the Apache HTTP Server, and seven Squid cache servers. Wikipedia currently runs on dedicated clusters of Linux servers (mainly Ubuntu), with a few OpenSolaris machines for ZFS. As of December 2009, there were 300 in Florida and 44 in Amsterdam. By January 22, 2013, Wikipedia had migrated its primary data server to an Equinix facility in Ashburn, Virginia.



Internal research and operational development
In accordance with growing amounts of incoming donations exceeding seven digits in 2013 as recently reported, the Foundation has reached a threshold of assets which qualify its consideration under the principles of industrial organization economics indicating the need for the re-investment of donations into the internal research and development of the Foundation. Two of the recent projects of such internal research and development have been the creation of a Visual Editor and a largely under-utilized "Thank" tab which were developed for the purpose of ameliorating issues of editor attrition, which have met with limited success. The estimates for reinvestment by industrial organizations into internal research and development was studied by Adam Jaffe who recorded that the range of 4% to 25% annually was to be recommended, with high end technology requiring the higher level of support for internal reinvestment. At the 2013 level of contributions for Wikimedia presently documented as 45 million dollars, the computed budget level recommended by Jaffe and Caballero for reinvestment concerning internal research and development is between 1.8 million and 11.3 million dollars annually.

According to the Michael Porter five forces analysis framework for industry analysis, Wikipedia and its parent institution Wikimedia are known as "first movers" and "radical innovators" in the services provided and supported by an open-source, on-line encyclopedia. The "five forces" are centered around the issue of "competitive rivalry" within the encyclopedia industry where Wikipedia is seen as having redefined by its "radical innovation" the parameters of effectiveness applied to conventional encyclopedia publication. This is the first force of Porter's five forces analysis. The second force is the "threat of new entrants" with competitive services and products possibly arising on the internet or the web. As a "first mover", Wikipedia has largely eluded the emergence of a fast second to challenge its radical innovation and its standing as the central provider of the services which it offers through the World Wide Web. Porter's third force is the "threat of substitute products" and it is too early to identify Google's "Knowledge Graphs" as an effective competitor given the current dependence of "Knowledge Graphs" upon Wikipedia's free access to its open-source services. The fourth force in the Porter five forces analysis is the "bargaining power of consumers" who use the services provided by Wikipedia, which has historically largely been nullified by the Wikipedia founding principle of an open invitation to expand and edit its content expressed in its moniker of being "the encyclopedia which anyone can edit." The fifth force in the Porter five forces analysis is defined as the "bargaining power of suppliers" which is presently seen as the open domain of both the global internet as a whole and the resources of public libraries world-wide, and therefore it is not seen as a limiting factor in the immediate future of the further development of Wikipedia.

Content licensing
When the project was started in 2001, all text in Wikipedia was covered by GNU Free Documentation License (GFDL), a copyleft license permitting the redistribution, creation of derivative works, and commercial use of content while authors retain copyright of their work. GFDL was created for software manuals that come with free software programs that are licensed under GPL. This made it a poor choice for a general reference work; for example, the GFDL requires the reprints of materials from Wikipedia to come with a full copy of the GFDL license text. In December 2002, the Creative Commons license was released: it was specifically designed for creative works in general, not just for software manuals. The license gained popularity among bloggers and others distributing creative works on the Web. The Wikipedia project sought the switch to the Creative Commons. Because the two licenses, GFDL and Creative Commons, were incompatible, in November 2008, following the request of the project, the Free Software Foundation (FSF) released a new version of GFDL designed specifically to allow Wikipedia to by August 1, 2009. (A new version of GFDL automatically covers Wikipedia contents.) In April 2009, Wikipedia and its sister projects held a community-wide referendum which decided the switch in June 2009.

The handling of media files (e.g. image files) varies across language editions. Some language editions, such as the English Wikipedia, include non-free image files under fair use doctrine, while the others have opted not to, in part because of the lack of fair use doctrines in their home countries (e.g. in Japanese copyright law). Media files covered by free content licenses (e.g. Creative Commons' CC BY-SA) are shared across language editions via Wikimedia Commons repository, a project operated by the Wikimedia Foundation. Wikipedia's accommodation of varying international copyright laws regarding images has led some to observe that its photographic coverage of topics lags behind the quality of the encyclopedic text.

The Wikimedia Foundation is not a licensor of content, but merely a hosting service for the contributors (and licensors) of the Wikipedia. This position has been successfully defended in court.

Methods of access
Because Wikipedia content is distributed under an open license, anyone can reuse or re-distribute it at no charge. The content of Wikipedia has been published in many forms, both online and offline, outside of the Wikipedia website.
 * Websites – Thousands of "mirror sites" exist that republish content from Wikipedia: two prominent ones, that also include content from other reference sources, are Reference.com and Answers.com. Another example is Wapedia, which began to display Wikipedia content in a mobile-device-friendly format before Wikipedia itself did.
 * Mobile apps – A variety of mobile apps provide access to Wikipedia on hand-held devices, including both Android and iOS devices (see Wikipedia apps). (See also Mobile access.)
 * Search engines – Some web search engines make special use of Wikipedia content when displaying search results: examples include Bing (via technology gained from Powerset) and Duck Duck Go.
 * Compact discs, DVDs – Collections of Wikipedia articles have been published on optical discs. An English version, 2006 Wikipedia CD Selection, contained about 2,000 articles. The Polish-language version contains nearly 240,000 articles. There are German- and Spanish-language versions as well.  Also, "Wikipedia for Schools", the Wikipedia series of CDs / DVDs produced by Wikipedians and SOS Children, is a free, hand-checked, non-commercial selection from Wikipedia targeted around the UK National Curriculum and intended to be useful for much of the English-speaking world. The project is available online; an equivalent print encyclopedia would require roughly 20 volumes.
 * Books – There are efforts to put a select subset of Wikipedia's articles into printed book form. Since 2009, tens of thousands of print on demand books which reproduced English, German, Russian and French Wikipedia articles have been produced by the American company Books LLC and by three Mauritian subsidiaries of the German publisher VDM.
 * Semantic Web – The website DBpedia, begun in 2007, extracts data from the infoboxes and category declarations of the English-language Wikipedia. Wikimedia has created the Wikidata project with a similar objective of storing the basic facts from each page of wikipedia and the other WMF wikis and make it available in a queriable semantic format, RDF. This is still under development. As of Feb 2014 it has 15,000,000 items and 1,000 properties for describing them.

Obtaining the full contents of Wikipedia for reuse presents challenges, since direct cloning via a web crawler is discouraged. Wikipedia publishes "dumps" of its contents, but these are text-only; as of 2007 there is no dump available of Wikipedia's images.

Several languages of Wikipedia also maintain a reference desk, where volunteers answer questions from the general public. According to a study by Pnina Shachaf in the Journal of Documentation, the quality of the Wikipedia reference desk is comparable to a standard library reference desk, with an accuracy of 55%.

Mobile access

 * See also: 

Wikipedia's original medium was for users to read and edit content using any standard web browser through a fixed Internet connection. Although Wikipedia content is now accessible through the mobile web since July 2013, The New York Times on 9 February 2014 quoted Erik Moller, deputy director of the Wikimedia Foundation, stating that the transition of internet traffic from desktops to mobile devices was significant and a cause for concern and worry. The The New York Times article reported the comparison statistics for mobile edits stating that, "Only 20 percent of the readership of the English-language Wikipedia comes via mobile devices, a figure substantially lower that the percentage of mobile traffic for other media sites, many of which approach 50 percent. And the shift to mobile editing has lagged even more." The New York Times reports that Mr. Moller of Wikimedia has assigned "a team of 10 software developers focused on mobile," out of a total of approximately 200 employees working at the Wikimedia Foundation. One principal concern cited by The New York Times for the "worry" is for Wikipedia to effectively address attrition issues with the number of editors which the on-line encyclopedia attracts to edit and maintain its content in a mobile access environment.

Access to Wikipedia from mobile phones was possible as early as 2004, through the Wireless Application Protocol (WAP), via the Wapedia service. In June 2007 Wikipedia launched en.mobile.wikipedia.org, an official website for wireless devices. In 2009 a newer mobile service was officially released, located at en.m.wikipedia.org, which caters to more advanced mobile devices such as the iPhone, Android-based devices or WebOS-based devices. Several other methods of mobile access to Wikipedia have emerged. Many devices and applications optimise or enhance the display of Wikipedia content for mobile devices, while some also incorporate additional features such as use of Wikipedia metadata (See ), such as geoinformation.

Wikipedia Zero is an initiative of the Wikimedia Foundation to expand the reach of the encyclopedia to the developing countries.

Readership
Wikipedia is extremely popular. In February 2014, The New York Times reported that Wikipedia is ranked fifth globally among all websites stating, "With 18 billion page views and nearly 500 million unique visitors a month..., Wikipedia trails just Yahoo, Facebook, Microsoft and Google, the largest with 1.2 billion unique visitors."

According to the "Wikipedia Readership Survey 2011", the average Wikipedia reader is 36 years old, with a rough parity between genders. Almost half of Wikipedia readers visit the site more than five times a month, and a similar number of readers specifically look for Wikipedia in search engine results. Only about half of Wikipedia readers realize that Wikipedia is a non-profit.

Sister projects – Wikimedia
Wikipedia has also spawned several sister projects, which are also wikis run by the Wikimedia Foundation, also called Wikimedia projects: "In Memoriam: September 11 Wiki", created in October 2002, detailed the September 11 attacks; Wiktionary, a dictionary project, was launched in December 2002; Wikiquote, a collection of quotations, created a week after Wikimedia launched; and Wikibooks, a collection of collaboratively written free textbooks and annotated texts. Wikimedia has since started a number of other projects, including: Wikimedia Commons, a site devoted to free-knowledge multimedia; Wikinews, for citizen journalism; and Wikiversity, a project for the creation of free learning materials and the provision of online learning activities. Of these, only Commons has had success comparable to that of Wikipedia. Another sister project of Wikipedia, Wikispecies, is a catalogue of species. In 2012 Wikivoyage, an editable travel guide, and Wikidata, an editable knowledge base, launched.

Impact on publishing


The most obvious economic effect of Wikipedia has been the death of commercial encyclopedias, especially the printed versions, e.g. Encyclopaedia Britannica, which were unable to compete with a product that is essentially free. Nicholas Carr wrote a 2005 essay, "The amorality of Web 2.0", that criticized websites with user-generated content, like Wikipedia, for possibly leading to professional (and, in his view, superior) content producers going out of business, because "free trumps quality all the time". Carr wrote: "Implicit in the ecstatic visions of Web 2.0 is the hegemony of the amateur. I for one can't imagine anything more frightening." Others dispute the notion that Wikipedia, or similar efforts, will entirely displace traditional publications. For instance, Chris Anderson, the editor-in-chief of Wired Magazine, wrote in Nature that the "wisdom of crowds" approach of Wikipedia will not displace top scientific journals, with their rigorous peer review process.

There is also an ongoing debate about the influence of Wikipedia to the biography publishing business. "The worry is that, if you can get all that information from Wikipedia, what's left for biography?" Said Kathryn Hughes, professor of life writing at UEA and author of The Short Life and Long Times of Mrs Beeton and George Eliot: the Last Victorian.

Cultural significance
In addition to logistic growth in the number of its articles, Wikipedia has steadily gained status as a general reference website since its inception in 2001. According to Alexa and comScore, Wikipedia is among the ten most visited websites worldwide. The growth of Wikipedia has been fueled by its dominant position in Google search results; about 50% of search engine traffic to Wikipedia comes from Google, a good portion of which is related to academic research. The number of readers of Wikipedia worldwide reached 365 million at the end of 2009. The Pew Internet and American Life project found that one third of US Internet users consulted Wikipedia. In 2011 Business Insider gave Wikipedia a valuation of $4 billion if it ran advertisements.

Wikipedia's content has also been used in academic studies, books, conferences, and court cases. The Parliament of Canada's website refers to Wikipedia's article on same-sex marriage in the "related links" section of its "further reading" list for the Civil Marriage Act. The encyclopedia's assertions are increasingly used as a source by organizations such as the US federal courts and the World Intellectual Property Organization – though mainly for supporting information rather than information decisive to a case. Content appearing on Wikipedia has also been cited as a source and referenced in some US intelligence agency reports. In December 2008, the scientific journal RNA Biology launched a new section for descriptions of families of RNA molecules and requires authors who contribute to the section to also submit a draft article on the RNA family for publication in Wikipedia.

Wikipedia has also been used as a source in journalism, often without attribution, and several reporters have been dismissed for plagiarizing from Wikipedia.

In July 2007 Wikipedia was the focus of a 30-minute documentary on BBC Radio 4 which argued that, with increased usage and awareness, the number of references to Wikipedia in popular culture is such that the word is one of a select band of 21st-century nouns that are so familiar (Google, Facebook, YouTube) that they no longer need explanation and are on a par with such 20th-century words as hoovering or Coca-Cola.

On September 28, 2007, Italian politician Franco Grillini raised a parliamentary question with the minister of cultural resources and activities about the necessity of freedom of panorama. He said that the lack of such freedom forced Wikipedia, "the seventh most consulted website", to forbid all images of modern Italian buildings and art, and claimed this was hugely damaging to tourist revenues.



On September 16, 2007, The Washington Post reported that Wikipedia had become a focal point in the 2008 US election campaign, saying: "Type a candidate's name into Google, and among the first results is a Wikipedia page, making those entries arguably as important as any ad in defining a candidate. Already, the presidential entries are being edited, dissected and debated countless times each day." An October 2007 Reuters article, titled "Wikipedia page the latest status symbol", reported the recent phenomenon of how having a Wikipedia article vindicates one's notability.

Active participation also has an impact. Law students have been assigned to write Wikipedia articles as an exercise in clear and succinct writing for an uninitiated audience.

Awards
Wikipedia won two major awards in May 2004. The first was a Golden Nica for Digital Communities of the annual Prix Ars Electronica contest; this came with a €10,000 (£6,588; $12,700) grant and an invitation to present at the PAE Cyberarts Festival in Austria later that year. The second was a Judges' Webby Award for the "community" category. Wikipedia was also nominated for a "Best Practices" Webby award. On January 26, 2007, Wikipedia was also awarded the fourth highest brand ranking by the readers of “brandchannel.com”, receiving 15% of the votes in answer to the question "Which brand had the most impact on our lives in 2006?"

In September 2008, Wikipedia received Quadriga A Mission of Enlightenment award of Werkstatt Deutschland along with Boris Tadić, Eckart Höfling, and Peter Gabriel. The award was presented to Wales by David Weinberger.

Satire


Many parodies target Wikipedia's openness and susceptibility to inserted inaccuracies, with characters vandalizing or modifying the online encyclopedia project's articles.

Comedian Stephen Colbert has parodied or referenced Wikipedia on numerous episodes of his show The Colbert Report and coined the related term wikiality, meaning "together we can create a reality that we all agree on—the reality we just agreed on". Another example can be found in a front-page article in The Onion in July 2006, with the title "Wikipedia Celebrates 750 Years of American Independence". "My Number One Doctor", a 2007 episode of the TV show Scrubs, played on the perception that Wikipedia is an unreliable reference tool with a scene in which Dr. Perry Cox reacts to a patient who says that a Wikipedia article indicates that the raw food diet reverses the effects of bone cancer by retorting that the same editor who wrote that article also wrote the Battlestar Galactica episode guide.

In 2008, the comedic website CollegeHumor produced a video sketch named "Professor Wikipedia", in which the fictitious Professor Wikipedia instructs a class with a medley of unverifiable and occasionally absurd statements.

The Dilbert comic strip from May 8, 2009, features a character supporting an improbable claim by saying "Give me ten minutes and then check Wikipedia."

In July 2009, BBC Radio 4 broadcast a comedy series called Bigipedia, which was set on a website which was a parody of Wikipedia. Some of the sketches were directly inspired by Wikipedia and its articles.

In 2010, comedian Daniel Tosh encouraged viewers of his show, Tosh.0, to visit the show's Wikipedia article and edit it at will. On a later episode, he commented on the edits to the article, most of them offensive, which had been made by the audience and had prompted the article to be locked from editing.

On August 23, 2013, the New Yorker website published a cartoon with this caption: "Dammit, Manning, have you considered the pronoun war that this is going to start on your Wikipedia page?"

Scientific use
In computational linguistics, information retrieval and natural language processing, Wikipedia has seen widespread use as a corpus for linguistic research. In particular, it commonly serves as a target knowledge base for the entity linking problem, which is then called "wikification", and to the related problem of word sense disambiguation. Methods similar to wikification can in turn be used to find "missing" links in Wikipedia.

Related projects
A number of interactive multimedia encyclopedias incorporating entries written by the public existed long before Wikipedia was founded. The first of these was the 1986 BBC Domesday Project, which included text (entered on BBC Micro computers) and photographs from over 1 million contributors in the UK, and covered the geography, art, and culture of the UK. This was the first interactive multimedia encyclopedia (and was also the first major multimedia document connected through internal links), with the majority of articles being accessible through an interactive map of the UK. The user interface and part of the content of the Domesday Project were emulated on a website until 2008.

One of the most successful early online encyclopedias incorporating entries by the public was h2g2, which was created by Douglas Adams. The h2g2 encyclopedia is relatively light-hearted, focusing on articles which are both witty and informative. Everything2 was created in 1998. All of these projects had similarities with Wikipedia, but were not wikis and neither gave full editorial privileges to public users.

GNE, an encyclopedia which was not a wiki, also created in January 2001, co-existed with Nupedia and Wikipedia early in its history; however, it has been retired.

Other websites centered on collaborative knowledge base development have drawn inspiration from Wikipedia. Some, such as Susning.nu, Enciclopedia Libre, Hudong, and Baidu Baike likewise employ no formal review process, although some like Conservapedia are not as open. Others use more traditional peer review, such as Encyclopedia of Life and the online wiki encyclopedias Scholarpedia and Citizendium. The latter was started by Sanger in an attempt to create a reliable alternative to Wikipedia. Scholarpedia also focuses on ensuring high quality.

Academic studies

 * Jensen, Richard. "Military History on the Electronic Frontier: Wikipedia Fights the War of 1812", The Journal of Military History 76#4 (October 2012): 523–556; online version.
 * (A blog post by the author.)
 * Priedhorsky, Reid, Jilin Chen, Shyong (Tony) K. Lam, Katherine Panciera, Loren Terveen, and John Riedl. "Creating, Destroying, and Restoring Value in Wikipedia". Proc. GROUP 2007;
 * Rosenzweig, Roy. Can History be Open Source? Wikipedia and the Future of the Past. (Originally published in The Journal of American History 93.1 (June 2006): 117–46.)
 * Priedhorsky, Reid, Jilin Chen, Shyong (Tony) K. Lam, Katherine Panciera, Loren Terveen, and John Riedl. "Creating, Destroying, and Restoring Value in Wikipedia". Proc. GROUP 2007;
 * Rosenzweig, Roy. Can History be Open Source? Wikipedia and the Future of the Past. (Originally published in The Journal of American History 93.1 (June 2006): 117–46.)
 * Rosenzweig, Roy. Can History be Open Source? Wikipedia and the Future of the Past. (Originally published in The Journal of American History 93.1 (June 2006): 117–46.)
 * Rosenzweig, Roy. Can History be Open Source? Wikipedia and the Future of the Past. (Originally published in The Journal of American History 93.1 (June 2006): 117–46.)

Books

 * (See book review by Baker, as listed hereafter.)
 * (Substantial criticisms of Wikipedia and other web 2.0 projects.)
 * Listen to:
 * The NPR interview with A. Keen, Weekend Edition Saturday, June 16, 2007.
 * Sheizaf Rafaeli & Yaron Ariel (2008). "Online motivational factors: Incentives for participation and contribution in Wikipedia." In
 * Listen to:
 * The NPR interview with A. Keen, Weekend Edition Saturday, June 16, 2007.
 * Sheizaf Rafaeli & Yaron Ariel (2008). "Online motivational factors: Incentives for participation and contribution in Wikipedia." In
 * Sheizaf Rafaeli & Yaron Ariel (2008). "Online motivational factors: Incentives for participation and contribution in Wikipedia." In
 * Sheizaf Rafaeli & Yaron Ariel (2008). "Online motivational factors: Incentives for participation and contribution in Wikipedia." In

Book reviews and other articles

 * Baker, Nicholson. "The Charms of Wikipedia". The New York Review of Books, March 20, 2008. Retrieved December 17, 2008. (Book rev. of The Missing Manual, by John Broughton, as listed previously.)
 * Crovitz, L. Gordon. "Wikipedia's Old-Fashioned Revolution: The online encyclopedia is fast becoming the best." (Originally published in Wall Street Journal online – April 6, 2009.)

Learning resources


 * Wikiversity list of learning resources. (Includes related courses, Web-based seminars, slides, lecture notes, text books, quizzes, glossaries, etc.)
 * The Great Book of Knowledge, Part 1: A Wiki is a Kind of Bus, Ideas, with Paul Kennedy, CBC Radio One, originally broadcast January 15, 2014. Webpage includes a link to the archived audio program (also found here). The radio documentary discusses Wikipedia's history, development and its place within the broader scope of the trend to democratized knowledge. It also includes interviews with several key Wikipedia staff and contributors, including Kat Walsh and Sue Gardner (audio, 53:58, Flash required).

Other media coverage


 * See Who's Editing Wikipedia – Diebold, the CIA, a Campaign , WIRED, August 14, 2007.
 * Is Wikipedia Cracking Up? The Independent, February 3, 2009.
 * Wikipedia probe into paid-for 'sockpuppet' entries , BBC News, October 21, 2013.
 * The Decline of Wikipedia , MIT Technology Review, October 22, 2013.
 * Is Wikipedia Cracking Up? The Independent, February 3, 2009.
 * Wikipedia probe into paid-for 'sockpuppet' entries , BBC News, October 21, 2013.
 * The Decline of Wikipedia , MIT Technology Review, October 22, 2013.
 * Is Wikipedia Cracking Up? The Independent, February 3, 2009.
 * Wikipedia probe into paid-for 'sockpuppet' entries , BBC News, October 21, 2013.
 * The Decline of Wikipedia , MIT Technology Review, October 22, 2013.
 * Is Wikipedia Cracking Up? The Independent, February 3, 2009.
 * Wikipedia probe into paid-for 'sockpuppet' entries , BBC News, October 21, 2013.
 * The Decline of Wikipedia , MIT Technology Review, October 22, 2013.