Broadly, a citation is a reference to a published or unpublished source (not always the original source). More precisely, a citation is an abbreviated alphanumeric expression (e.g. [Newell84]) embedded in the body of an intellectual work that denotes an entry in the bibliographic references section of the work for the purpose of acknowledging the relevance of the works of others to the topic of discussion at the spot where the citation appears. Generally the combination of both the in-body citation and the bibliographic entry constitutes what is commonly thought of as a citation (whereas bibliographic entries by themselves are not).

Citation has several important purposes: to uphold intellectual honesty,^[1] to attribute prior or unoriginal work and ideas to the correct sources, to allow the reader to determine independently whether the referenced material supports the author's argument in the claimed way, and to help the reader gauge the strength and validity of the material the author has used.^[2]

The forms of citations generally subscribe to one of the generally accepted citations systems, such as the Oxford,^[3] Harvard, MLA, American Sociological Association (ASA), American Psychological Association (APA), and other citations systems, as their syntactic conventions are widely known and easily interpreted by readers. Each of these citation systems has its respective advantages and disadvantages relative to the trade-offs of being informative (but not too disruptive) and thus are chosen relative to the needs of the type of publication being crafted. Editors will often specify the citation system to use.

Bibliographies, and other list-like compilations of references, are generally not considered citations because they do not fulfil the true spirit of the term: deliberate acknowledgement by other authors of the priority of one's ideas.^[4]

Concepts[link]

• A bibliographic citation is a reference to a book, article, web page, or other published item. Citations should supply sufficient detail to identify the item uniquely.^[5] Different citation systems and styles are used in scientific citation, legal citation, prior art, and the arts and the humanities.

Citation content[link]

Citation content can vary depending on the type of source and may include:

• Book: author(s), book title, publisher, date of publication, and page number(s) if appropriate.^[6][7]
• Journal: author(s), article title, journal title, date of publication, and page number(s).
• Newspaper: author(s), article title, name of newspaper, section title and page number(s) if desired, date of publication.
• Web site: author(s), article and publication title where appropriate, as well as a URL, and a date when the site was accessed.
• Play: inline citations offer part, scene, and line numbers, the latter separated by periods: 4.452 refers to scene 4, line 452. For example, "In Eugene Onegin, Onegin rejects Tanya when she is free to be his, and only decides he wants her when she is already married" (Pushkin 4.452-53).^[8]
• Poem: spaced slashes are normally used to indicate separate lines of a poem, and parenthetical citations usually include the line number(s). For example: "For I must love because I live / And life in me is what you give." (Brennan, lines 15–16).^[8]

Unique identifiers[link]

Along with information such as author(s), date of publication, title and page numbers, citations may also include unique identifiers depending on the type of work being referred to.

• Citations of books may include an International Standard Book Number (ISBN).
• Specific volumes, articles or other identifiable parts of a periodical, may have an associated Serial Item and Contribution Identifier (SICI).
• Electronic documents may have a digital object identifier (DOI).
• Biomedical research articles may have a PubMed Identifier (PMID).
• A citation number, used in some citation systems, is a number or symbol added inline and usually in superscript, to refer readers to a footnote or endnote that cites the source. In other citation systems, an inline parenthetical reference is used rather than a citation number, with limited information such as the author's last name, year of publication, and page number referenced; a full identification of the source will then appear in an appended bibliography.

Citation systems[link]

Broadly speaking, there are two citation systems:^[9][10][11]

Note systems[link]

Note systems involve the use of sequential numbers in the text which refer to either footnotes (notes at the end of the page) or endnotes (a note on a separate page at the end of the paper) which gives the source detail. The notes system may or may not require a full bibliography, depending on whether the writer has used a full note form or a shortened note form.

For example, an excerpt from the text of a paper using a notes system without a full bibliography could look like this:

"The five stages of grief are denial, anger, bargaining, depression, and acceptance."¹

The note, located either at the foot of the page (footnote) or at the end of the paper (endnote) would look like this:

1. Elisabeth Kübler-Ross, On Death and Dying (New York: Macmillan, 1969) 45–60.

In a paper which contains a full bibliography, the shortened note could look like this:

1. Kübler-Ross, On Death and Dying 45–60.

and the bibliography entry, which would be required with a shortened note, would look like this:

Kübler-Ross, Elisabeth. On Death and Dying. New York: Macmillan, 1969.

In the humanities, many authors use footnotes or endnotes to supply anecdotal information. In this way, what looks like a citation is actually supplementary material, or suggestions for further reading.^[12]

Parenthetical referencing[link]

Parenthetical referencing also known as Harvard referencing where full or partial, in-text citations are enclosed within parentheses and embedded in the paragraph, as opposed to the footnote style.

An example of a parenthetical reference would be:

(Smith 2010, p. 1)

Depending on the choice of style, fully cited parenthetical references may require no end section. Alternately a list of the citations with complete bibliographical references may be included in an end section sorted alphabetically by author's last name.

This section may be known as:

• References
• Bibliography
• Works cited
• Works consulted

However, the in-text referencing style in online publications may differ from the conventional parenthetical referencing. A full reference can be hidden and displayed in the form of a tooltip on a reader’s request.^[13] This style makes citing easier and improves the reader’s experience.

Citation styles[link]

Citation styles can be broadly divided into styles common to the Humanities and the Sciences, though there is considerable overlap. Some style guides, such as the Chicago Manual of Style, are quite flexible and cover both parenthetical and note citation systems.^[11] Others, such as MLA and APA styles, specify formats within the context of a single citation system.^[10] These may be referred to as citation formats as well as citation styles.^[14][15][16] The various guides thus specify order of appearance, for example, of publication date, title, and page numbers following the author name, in addition to conventions of punctuation, use of italics, emphasis, parenthesis, quotation marks, etc., particular to their style.

A number of organizations have created styles to fit their needs; consequently, a number of different guides exist. Individual publishers often have their own in-house variations as well, and some works are so long-established as to have their own citation methods too: Stephanus pagination for Plato; Bekker numbers for Aristotle; citing the Bible by book, chapter and verse; or Shakespeare notation by play, act and scene.

Some examples of style guides include:

Humanities[link]

• The Chicago Style (CMOS) was developed and its guide is The Chicago Manual of Style. It is most widely used in history and economics as well as some social sciences. Its derivative is the closely related Turabian style which is designed for student references and is distinguished from the CMOS by omission of quotation marks in reference lists and mandatory access date citation.
• The Columbia Style was made by Janice R. Walker and Todd Taylor to give detailed guidelines for citing internet sources. Columbia Style offers models for both the humanities and the sciences.
• Evidence Explained: Citing History Sources from Artifacts to Cyberspace by Elizabeth Shown Mills covers primary sources not included in CMOS, such as censuses, court, land, government, business, and church records. Includes sources in electronic format. Used by genealogists and historians.^[17]
• Harvard referencing (or author-date system) is a specific kind of parenthetical referencing. Parenthetical referencing is recommended by both the British Standards Institution and the Modern Language Association. Harvard referencing involves a short author-date reference, e.g., "(Smith, 2000)", being inserted after the cited text within parentheses and the full reference to the source being listed at the end of the article.
• MLA style was developed by the Modern Language Association and is most often used in the arts and the humanities, particularly in English studies, other literary studies, including comparative literature and literary criticism in languages other than English ("foreign languages"), and some interdisciplinary studies, such as cultural studies, drama and theatre, film, and other media, including television. This style of citations and bibliographical format uses parenthetical referencing with author-page (Smith 395) or author-[short] title-page (Smith, Contingencies 42) in the case of more than one work by the same author within parentheses in the text, keyed to an alphabetical list of sources on a "Works Cited" page at the end of the paper, as well as notes (footnotes or endnotes). See The MLA Style Manual and The MLA Handbook for Writers of Research Papers, particularly Citation and bibliography format.^[18]
• The MHRA Style Guide is published by the Modern Humanities Research Association (MHRA) and most widely used in the arts and humanities in the United Kingdom, where the MHRA is based. It is available for sale both in the UK and in the United States. It is similar to MLA style, but has some differences. For example, MHRA style uses footnotes that reference a citation fully while also providing a bibliography. Some readers find it advantageous that the footnotes provide full citations, instead of shortened references, so that they do not need to consult the bibliography while reading for the rest of the publication details.^[19]

In some areas of the Humanities, footnotes are used exclusively for references, and their use for conventional footnotes (explanations or examples) is avoided. In these areas, the term "footnote" is actually used as a synonym for "reference", and care must be taken by editors and typesetters to ensure that they understand how the term is being used by their authors.

Law[link]

• The Bluebook is a citation system traditionally used in American academic legal writing, and the Bluebook (or similar systems derived from it) are used by many courts.^[20] At present, academic legal articles are always footnoted, but motions submitted to courts and court opinions traditionally use inline citations which are either separate sentences or separate clauses. Inline citations allow readers to quickly determine the strength of a source based on, for example, the court a case was decided in and the year it was decided.
• The legal citation style used almost universally in Canada is based on the Canadian Guide to Uniform Legal Citation (aka McGill Guide), published by McGill Law Journal.^[21]
• British legal citation almost universally follows the Oxford Standard for Citation of Legal Authorities (OSCOLA).

Sciences, mathematics, engineering, physiology, and medicine[link]

• The American Chemical Society style, or ACS style, is often used in chemistry and other physical sciences. In ACS style references are numbered in the text and in the reference list, and numbers are repeated throughout the text as needed.
• In the style of the American Institute of Physics (AIP style), references are also numbered in the text and in the reference list, with numbers repeated throughout the text as needed.
• Styles developed for the American Mathematical Society (AMS), or AMS styles, such as AMS-LaTeX, are typically implemented using the BibTeX tool in the LaTeX typesetting environment. Brackets with author’s initials and year are inserted in the text and at the beginning of the reference. Typical citations are listed in-line with alphabetic-label format, e.g. [AB90]. This type of style is also called a "Authorship trigraph."
• The Vancouver system, recommended by the Council of Science Editors (CSE), is used in medical and scientific papers and research.
  • In one major variant, that used by the American Society of Mechanical Engineers (ASME), citation numbers are included in the text in square brackets rather than as superscripts. All bibliographical information is exclusively included in the list of references at the end of the document, next to the respective citation number.
  • The International Committee of Medical Journal Editors (ICMJE) is reportedly the original kernel of this biomedical style which evolved from the Vancouver 1978 editors' meeting.^[22] The MEDLINE/PubMed database uses this citation style and the National Library of Medicine provides "ICMJE Uniform Requirements for Manuscripts Submitted to Biomedical Journals -- Sample References".^[23]
• The style of the Institute of Electrical and Electronics Engineers (IEEE), or IEEE style, encloses citation numbers within square brackets and numbers them consecutively, with numbers repeated throughout the text as needed.^[24]
• Pechenik Citation Style is a style described in A Short Guide to Writing about Biology, 6th ed. (2007), by Jan A. Pechenik.^[25]
• In 2006, Eugene Garfield proposed a bibliographic system for scientific literature, to consolidate the integrity of scientific publications.^[26]

Social sciences[link]

• The style of the American Psychological Association, or APA style, published in the Publication Manual of the American Psychological Association, is most often used in social sciences. APA style uses Harvard referencing within the text, listing the author's name and year of publication, keyed to an alphabetical list of sources at the end of the paper on a References page.
• The American Political Science Association publishes both a style manual and a style guide for publications in this field.^[27] The style is close to the CMOS.
• The American Anthropological Association utilizes a modified form of the Chicago Style laid out in their Publishing Style Guide.
• The ASA style of American Sociological Association is one of the main styles used in sociological publications.

Citation marks[link]

In the case of direct citations, the boundaries of a citation are apparent from the quotation marks. However, the boundaries of indirect citations are usually unknown. In order to clarify these boundaries, citation marks (˻…˼) can be used. Example:

This is sentence 1. ˻This is sentence 2. This is sentence 3.˼ (Smith et al., 2012)

Here, it becomes apparent from the citation marks that the citation refers to both sentence 2 and 3, but not to sentence 1.

Issues[link]

In their research on footnotes in scholarly journals in the field of communication, Michael Bugeja and Daniela V. Dimitrova have found that citations to online sources have a rate of decay (as cited pages are taken down), which they call a "half-life," that renders footnotes in those journals less useful for scholarship over time.^[28]

Other experts have found that published replications do not have as many citations as original publications.^[29]

Another important issue is citation errors, which often occur due to carelessness on either the researcher or journal editor's part in the publication procedure. Experts have found that simple precautions, such as consulting the author of a cited source about proper citations, reduce the likelihood of citation errors and thus increase the quality of research.^[30]

See also[link]

• Acknowledgment (creative arts)
• Bible citation
• Case citation
• Citation creator
• Citation signal
• Citationality
• Credit (creative arts)
• Cross-reference
• Scholarly method
• Source evaluation
• Style guide

Footnotes[link]

References[link]

External links[link]

Look up citation needed in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Citation needed

Guidelines

• Citing Government Documents/Government Agency Style Manuals, University of North Texas Libraries.
• Document it Citation and Referee AMS, and the AMSRefs package.
• Guide to Citation Style Guides
• ONLINE! Citation Styles (An online guide to different citation formats)
• "What is citation?", Turnitin.com
• "Cater all your Citation needs?", Makecitation.com

Examples

• Illustrated examples, generated using BibTeX, of several major styles, including more than those listed above.
• PDF file bibstyles.pdf illustrates how several bibliographic styles appear with citations and reference entries, generated using BibTeX.

Style guides

• [1]
• How to write footnotes, endnotes and electronic references in a proper format
• Swarthmore library's Guide to Citation Styles for Science and Humanities.

Other online resources

• thehistorysite.org Online resources for historical research and writing.

Wikipedia

150px The logo of Wikipedia, a globe featuring glyphs from many different writing systems
Screenshot  Screenshot of Wikipedia's multilingual portal.
URL	wikipedia.org
Slogan	The Free Encyclopedia
Commercial?	No
Type of site	Internet encyclopedia
Registration	Optional (required only for certain tasks such as editing protected pages, creating pages or uploading files)
Available language(s)	275 active editions (285 in total)
Content license	Creative Commons Attribution/ Share-Alike 3.0 (most text also dual-licensed under GFDL) Media licensing varies
Owner	Wikimedia Foundation (non-profit)
Created by	Jimmy Wales, Larry Sanger[1]
Launched	January 15, 2001 (2001-01-15) (11 years ago)
Alexa rank	6 (June 2012[update])[2]
Current status	Active

Wikipedia (ⁱ/ˌwɪkɨˈpiːdiə/ or ⁱ/ˌwɪkiˈpiːdiə/ WIK-i-PEE-dee-ə) is a free, collaboratively edited and multilingual Internet encyclopedia supported by the non-profit Wikimedia Foundation. Its 22 million articles (over 0 million in English alone) have been written collaboratively by volunteers around the world. Almost all of its articles can be edited by anyone with access to the site,^[3] and it has about 100,000 regularly active contributors.^[4][5] As of June 2012, there are editions of Wikipedia in 285 languages. It has become the largest and most popular general reference work on the Internet,^[6][7][8][9] ranking sixth globally among all websites on Alexa and having an estimated 365 million readers worldwide.^[6][10] It is estimated that Wikipedia receives 2.7 billion monthly pageviews from the United States alone.^[11]

Wikipedia was launched in January 2001 by Jimmy Wales and Larry Sanger.^[12] Sanger coined the name Wikipedia,^[13] which is a portmanteau of wiki (a type of collaborative website, from the Hawaiian word wiki, meaning "quick")^[14] and encyclopedia. Wikipedia's departure from the expert-driven style of encyclopedia building and the presence of a large body of unacademic content have received extensive attention in print media. In its 2006 Person of the Year article, Time magazine recognized the rapid growth of online collaboration and interaction by millions of people around the world. It cited Wikipedia as an example, in addition to YouTube, MySpace, and Facebook.^[15] Wikipedia has also been praised as a news source because of how quickly articles about recent events appear.^[16][17] Students have been assigned to write Wikipedia articles as an exercise in clearly and succinctly explaining difficult concepts to an uninitiated audience.^[18]

Although the policies of Wikipedia strongly espouse verifiability and a neutral point of view, criticisms leveled at Wikipedia include allegations about quality of writing,^[19] inaccurate or inconsistent information, and explicit content. Various experts (including founder Jimmy Wales and Jonathan Zittrain of Oxford University) have expressed concern over possible (intentional or unintentional) biases.^{[20][21][22][23]} These allegations are addressed by various Wikipedia policies.

Other disparagers of Wikipedia simply point out vulnerabilities inherent to any wiki that may be edited by anyone. These critics observe that much weight is given to topics that more editors are likely to know about, like popular culture,^[24] and that the site is vulnerable to vandalism,^[25][26] though some studies indicate that vandalism is quickly deleted. Critics point out that some articles contain unverified or inconsistent information,^[27] though a 2005 investigation in Nature showed that the science articles they compared came close to the level of accuracy of Encyclopædia Britannica and had a similar rate of "serious errors".^[28]

History[link]

Wikipedia originally developed from another encyclopedia project, Nupedia.

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, Inc, a web portal company. Its main figures were Jimmy Wales, Bomis CEO, 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.^[29] Larry Sanger and Jimmy Wales founded Wikipedia.^[30][31] While Wales is credited with defining the goal of making a publicly editable encyclopedia,^[32][33] Sanger is usually credited with the strategy of using a wiki to reach that goal.^[34] On January 10, 2001, Sanger proposed on the Nupedia mailing list to create a wiki as a "feeder" project for Nupedia.^[35] Wikipedia was formally launched on January 15, 2001, as a single English-language edition at www.wikipedia.com,^[36] and announced by Sanger on the Nupedia mailing list.^[32] Wikipedia's policy of "neutral point-of-view"^[37] was codified in its initial months, and was similar to Nupedia's earlier "nonbiased" policy. Otherwise, there were relatively few rules initially and Wikipedia operated independently of Nupedia.^[32]

Number of articles in the English Wikipedia (in blue)

Wikipedia gained early contributors from Nupedia, Slashdot postings, and web search engine indexing. It grew to approximately 20,000 articles and 18 language editions by the end of 2001. By late 2002, it had reached 26 language editions, 46 by the end of 2003, and 161 by the final days of 2004.^[38] 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 two million-article mark on September 9, 2007, making it the largest encyclopedia ever assembled, eclipsing even the 1407 Yongle Encyclopedia, which had held the record for exactly 600 years.^[39]

Citing fears of commercial advertising and lack of control in a perceived English-centric^{[citation needed]} Wikipedia, users of the Spanish Wikipedia forked from Wikipedia to create the Enciclopedia Libre in February 2002.^[40] These moves encouraged Wales to announce that Wikipedia would not display advertisements, and change Wikipedia's domain from wikipedia.com to wikipedia.org.^[41]

Growth of the number of articles in the English Wikipedia (in blue)

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.^[42] Around 1,800 articles were added daily to the encyclopedia in 2006; by 2010 that average was roughly 1,000.^[43] A team at the Palo Alto Research Center attributed this slowing of growth to the project's increasing exclusivity and resistance to change.^[44] 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.^[45][46]

In November 2009, a researcher at the Rey Juan Carlos University in Madrid 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.^[47][48] The Wall Street Journal reported that "unprecedented numbers of the millions of online volunteers who write, edit and police [Wikipedia] are quitting". The array of rules applied to editing and disputes related to such content are among the reasons for this trend that are cited in the article.^[49] Jimmy Wales disputed these claims in 2009, denying the decline and questioning the methodology of the study.^[50] 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.^[51] Nevertheless, in the same interview he claimed the number of editors was "stable and sustainable".

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 Inc. With 42.9 million unique visitors, Wikipedia was ranked No. 9, surpassing the New York Times (#10) and Apple Inc. (#11). This marked a significant increase over January 2006, when the rank was No. 33, with Wikipedia receiving around 18.3 million unique visitors.^[52] As of May 2012, Wikipedia is the sixth-most-popular website worldwide according to Alexa Internet,^[53] receiving more than 2.7 billion U.S. pageviews every month,^[11] out of a global monthly total of over 12 billion pageviews.^[54]

Wikipedia blackout protest against SOPA on January 18, 2012

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.^[55] More than 162 million people viewed the blackout explanation page that temporarily replaced Wikipedia content.^[56][57]

Nature[link]

Editing[link]

In April 2009, the Wikimedia Foundation conducted a Wikipedia usability study, questioning users about the editing mechanism.^[59]

In a departure from the style of traditional encyclopedias, Wikipedia employs an open, "wiki" editing model^[clarify]. This means that, except for particularly sensitive and/or vandalism-prone pages, which would be "protected" from some degree of editing, the reader of an article can edit the text as he sees fits, anonymously or with a user account. Different language editions modify this policy; for example, only registered users may create a new article in the English edition. No article is owned by its creator or any other editor, nor is any vetted by any recognized authority. Instead, editors agree on the content and structure of articles by consensus.^[60]

By default, an edit to an article becomes available immediately, prior to any review. As such, an article may contain inaccuracies, ideological biases, or even patent nonsense, until or unless another editor corrects the problem. Different language editions, each under separate administrative control, are free to modify this policy. For example, the German Wikipedia maintains "stable versions" of articles,^[61] which have passed certain reviews. Notably, however, the English Wikipedia does not use the German model. In 2010 the former conducted a two-month trial of a "pending changes" system wherein new users' edits to certain "controversial" or vandalism-prone articles would be "subject to review from an established Wikipedia editor before publication". In a discussion following the trial, the community failed to reach consensus as to whether or not to keep the "pending changes" system. Thus, all remaining pending changes were removed from article pages in May 2011.^[62]

Editors keep track of changes to articles by checking the difference between two revisions of a page, displayed here in red.

Contributors, whether registered or not, can take advantage of features available in the software that powers Wikipedia. The "History" page belonging to each article records every single past revision of the article, though a revision with libelous content, criminal threats or copyright infringements may be removed retroactively.^[63][64] Editors can use this page to undo undesirable changes or restore lost content. The "Talk" page associated with each article helps coordinate work among multiple editors.^[65] Importantly, editors may use the "Talk" page to reach "consensus"^[66], sometimes through the use of polling.

In addition, editors may view the most "recent changes" to the website, which are displayed in reverse chronology. Regular contributors often maintain a "watchlist" of articles of interest to them, in order to easily track recent changes to those articles. In language editions with many articles, editors tend to prefer the "watchlist" because the number of edits has become too large to follow in "recent changes." New page patrol is "a process by which newly created articles are checked for obvious problems."^[67] A frequently vandalized article can be semi-protected, allowing only well established users to edit it.^[68] A particularly contentious article may be locked so that only administrators are able to make changes.^[69]

The editing interface of Wikipedia.

Computer programs called bots have been used widely to correct 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 that are designed to detect attacks and fix them automatically (or semi-automatically), filters that warn users making "undesirable" edits,^[70] blocks on the creation of links to particular websites, and blocks on edits from particular accounts, IP addresses or address ranges.

Organization of article pages[link]

Articles in Wikipedia are loosely organized according to their development status and subject matter. Categories help organize each article by its content and properties.^[71] 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.^[72][73] Researcher Giacomo Poderi found that articles tend to reach featured status via the intensive work of few editors.^[74] 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.^[75]

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[link]

The most common and obvious types of vandalism include insertion of false information, advertising language, highly partisan or opinionated language, or other types of spam.^[76] Sometimes editors commit vandalism by removing information or entirely blanking a given page. Less common types of vandalism can be more difficult to detect. Those committing vandalism 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.

The opportunity for vandalism provides a number of unique challenges to Wikipedia. One particular criticism is that, at any moment, a reader of an article cannot be certain that it has not been compromised by the insertion of false information or the removal of essential information. Former Encyclopædia Britannica editor-in-chief Robert McHenry once described the predicament using simile:^[77]

The user who visits Wikipedia to learn about some subject, to confirm some matter of fact, is rather in the position of a visitor to a public restroom. It may be obviously dirty, so that he knows to exercise great care, or it may seem fairly clean, so that he may be lulled into a false sense of security. What he certainly does not know is who has used the facilities before him.^[78]

John Seigenthaler has described Wikipedia as "a flawed and irresponsible research tool".^[79]

Obvious vandalism is generally easy to remove from wiki articles; in practice, the median time to detect and fix vandalism is a few minutes^[25][26]. However, in one high-profile incident, false information was introduced into the biography of American political figure John Seigenthaler and remained undetected for four months.^[79] John Seigenthaler, the founding editorial director of USA Today and founder of the Freedom Forum First Amendment Center at Vanderbilt University, called Jimmy Wales and asked if Wales had any way of knowing who contributed the misinformation. Wales replied that he did not, although the perpetrator was eventually traced.^[80][81] This incident led to policy changes on the site, specifically targeted at tightening up the verifiability of all biographical articles of living people.

Rules and laws governing content and editor behavior[link]

Content in Wikipedia is subject to the laws (in particular, the copyright laws) of the United States and of the U.S. state of Florida, where the majority of Wikipedia's servers reside. Beyond legal matters, the editorial principles of Wikipedia are embodied in the "five pillars", and numerous policies and guidelines 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.^[82] Editors can enforce rules 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.

English Wikipedia[link]

Main Page of the English Wikipedia on October 20, 2010.

Content policies[link]

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.^[83] A topic should also meet Wikipedia's standards of "notability",^[84] 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 only to convey knowledge that is already established and recognized.^[85] 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.^[86] This can lead to the removal of information that is valid, thus hindering inclusion of knowledge and growth of the encyclopedia.^[87] Finally, Wikipedia must not take a side.^[88] All opinions and viewpoints, if attributable to external sources, must enjoy an appropriate share of coverage within an article.^[89] This is known as neutral point of view (NPOV).

Dispute resolution[link]

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, an edit war may begin, in which a change is repeatedly done by one editor and then undone by another.

In order to gain a broader community consensus, editors can raise issues at the Village Pump, or initiate a Request for Comment. An editor can report impolite, uncivil, or otherwise problematic communications with another editor via the "Wikiquette Assistance" noticeboard. Such postings themselves have no binding or disciplinary power. Specialized forums exist for centralizing discussion on specific decisions, such as whether or not an article should be deleted. Mediation is sometimes used, although it has been deemed by some Wikipedians to be unhelpful for resolving particularly contentious disputes.

Arbitration[link]

The Arbitration Committee is the ultimate dispute resolution method. Although disputes usually arise from a disagreement between two opposing views on how articles should read^{[citation needed]}, 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,^[90] 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.^[91]

Privacy[link]

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.^[92] It is somewhat of a battle between the right to be anonymous in cyberspace and the right to be anonymous in real life ("meatspace"). Wikipedia Watch argues that "Wikipedia is a potential menace to anyone who values privacy" and that "a greater degree of accountability in the Wikipedia structure" would be "the very first step toward resolving the privacy problem."^[93] A particular problem occurs in the case of an individual who is relatively unimportant and for whom there exists a Wikipedia page against their 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 who was formerly with the Chaos Computer Club. More specifically, the court ordered that the URL within the German .de domain (http://www.wikipedia.de/) may no longer redirect to the encyclopedia's servers in Florida at http://de.wikipedia.org although German readers were still able to use the US-based URL directly, and there was virtually no loss of access on their part. The court order arose out of a lawsuit filed by Floricic's parents, demanding that their son's surname be removed from Wikipedia.^[94] 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 were being violated.^[95] The plaintiffs appealed to the Berlin state court, but were refused in May 2006.

Community[link]

Wikimania, an annual conference for users of Wikipedia and other projects operated by the Wikimedia Foundation.

Wikipedia's community has been described as "cult-like,"^[96] although not always with entirely negative connotations,^[97] and criticized for failing to accommodate inexperienced users.^[98] The project's preference for cohesiveness, even if it requires compromise that includes disregard of credentials, has been referred to as "anti-elitism".^[99]

Power structure[link]

The Wikipedia community has established "a bureaucracy of sorts", including "a clear power structure that gives volunteer administrators the authority to exercise editorial control."^{[100][101][102]} Editors in good standing in the community can run for one of many levels of volunteer stewardship; this begins with "administrator,"^[103][104] 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 do not enjoy any special privilege in decision-making; instead they 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).^[105][106]

Contributors[link]

Demographics of Wikipedia editors.

Wikipedia does not require that its users provide identification.^[107] However, as Wikipedia grows with its unconventional model of encyclopedia building, "Who writes Wikipedia?" has become one of the questions frequently asked on the project, often with a reference to other Web 2.0 projects such as Digg.^[108] Jimmy 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 are 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.^[109] 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."^[110] Although some contributors are authorities in their field, Wikipedia requires that even their contributions be supported by published and verifiable sources.

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 a "creative construction" approach encourages participation.^{[clarification needed][111]} In his 2008 book, The Future of the Internet and How to Stop It, Jonathan Zittrain of the Oxford Internet Institute and Harvard Law School’s Berkman Center for Internet & Society cites Wikipedia's success as a case study in how open collaboration has fostered innovation on the web.^[112] A 2008 study found that Wikipedians were less agreeable, open, and conscientious than others.^[113][114] A 2009 study suggested there was "evidence of growing resistance from the Wikipedia community to new content."^[115]

At OOPSLA 2009, Wikimedia CTO and Senior Software Architect Brion Vibber gave a presentation entitled "Community Performance Optimization: Making Your People Run as Smoothly as Your Site"^[116] in which he discussed the challenges of handling the contributions from a large community and compared the process to that of software development.

Interactions[link]

Wikipedians and British Museum curators collaborate on the article Hoxne Hoard in June 2010.

Members of the community predominantly interact with each other via 'talk' pages, which are wiki-edited pages which are associated with articles, as well as via talk pages that are specific to particular contributors, and talk pages that help run the site. These pages help the contributors reach consensus about what the contents of the articles should be, how the site's rules may change, and to take actions with respect to any problems within the community.^[117]

The Wikipedia Signpost is the community newspaper on the English Wikipedia,^[118] and was founded by Michael Snow, an administrator and the former chair of the Wikimedia Foundation board of trustees.^[119] It covers news and events from the site, as well as major events from sister projects, such as Wikimedia Commons.^[120]

Positive re-inforcement[link]

Wikipedians sometimes award one another barnstars for good work. These personalized tokens of appreciation reveal 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 by researchers seeking to determine what implications it might have for other communities engaged in large-scale collaborations.^[121]

New users[link]

60% of registered users never make another edit after their first 24 hours. Possible explanations are that such users only register for a single purpose, or are scared away by their experiences.^[122] 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,^[123] 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,"^[124] but the contribution histories of IP addresses cannot necessarily with any certainty be credited to, or blamed upon, a particular user.

A 2009 study by Business Insider editor and journalist Henry Blodget^[125] showed that in a random sample of articles most content in Wikipedia (measured by the amount of contributed text which 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).

Demographics[link]

One study found that the contributor base to Wikipedia "was barely 13% women; the average age of a contributor was in the mid-20s." Sue Gardner, Executive Director of the Wikimedia Foundation, hopes to see female editing contributions increase to 25% by 2015.^[126] 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% or greater).^[127]

Estimation of contributions shares from different regions in the world to different Wikipedia editions.

In a research article published in PLoS ONE in 2012, Yasseri et al. based on the circadian patterns of editorial activities of the community, have 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 25% in Simple English Wikipedia. The article also covers some other editions in different languages.^[128] The Wikimedia Foundation hopes to increase the number of editors in the Global South to 37% by 2015.^[129]

Language editions[link]

Percentage of all Wikipedia articles in English (red) and top ten largest language editions (blue). As of July 2007 less than 23% of Wikipedia articles are in English.

There are currently 285 language editions (or language versions) of Wikipedia; of these, 4 have over 1 million articles each (English, German, French and Dutch), 6 more have over 700,000 articles (Italian, Polish, Spanish, Russian, Japanese and Portuguese), 40 more have over 100,000 articles and 109 have over 10,000 articles.^[130] The largest, the English Wikipedia, has over 0 million articles. According to Alexa, the English subdomain (en.wikipedia.org; English Wikipedia) receives approximately 54% of Wikipedia's cumulative traffic, with the remaining split among the other languages (Japanese: 10%, German: 8%, Spanish: 5%, Russian: 4%, French: 4%, Italian: 3%).^[6] As of January 2012, the five largest language editions are (in order of article count) English, German, French, Dutch, and Italian Wikipedias.^[131]

Since Wikipedia is web-based 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. color vs. colour)^[132] or points of view.^[133] 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.^{[134][135][136]}

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."^[137] 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).^[138] For instance, Meta-Wiki provides important statistics on all language editions of Wikipedia,^[139] and it maintains a list of articles every Wikipedia should have.^[140] The list concerns basic content by subject: biography, history, geography, society, culture, science, technology, foodstuffs, 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.^[141] Articles available in more than one language may offer "Interwiki links", which link to the counterpart articles in other editions.

Analysis of content[link]

Although poorly-written articles are flagged for improvement,^[142] 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, not argue value judgements, yet some draw the censorship line^[143] more strictly than do articles focusing on unpleasant, highly specialized, arguably trivial, or arguably objectionable material. In 2006, the Wikipedia Watch criticism website listed dozens of examples of plagiarism by Wikipedia editors on the English version.^[144] Wikipedia co-founder Jimmy Wales has said in this respect: "We need to deal with such activities with absolute harshness, no mercy, because this kind of plagiarism is 100% at odds with all of our core principles."^[144]

Accuracy of content[link]

Articles for traditional encyclopedias such as Encyclopædia Britannica are carefully and deliberately written by experts, lending such encyclopedias a reputation for accuracy. On the other hand, Wikipedia is often cited for factual inaccuracies and misrepresentations. However, a non-scientific report in the journal Nature in 2005 suggested that for some scientific articles Wikipedia came close to the level of accuracy of Encyclopædia Britannica and had a similar rate of "serious errors."^[28] These claims have been disputed by, among others, Encyclopædia Britannica.^[145][146] The Nature report also concluded that the structure of Wikipedia's articles was often poor.

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.^[147] Concerns have been raised regarding the lack of accountability that results from users' anonymity,^[148] the insertion of spurious information,^[149] 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.^[150]

Critics argue that Wikipedia's open nature and a lack of proper sources for most of the information makes it unreliable.^[151] Some commentators suggest that Wikipedia may be reliable, but that the reliability of any given article is not clear.^[152] Editors of traditional reference works such as theEncyclopædia Britannica have questioned the project's utility and status as an encyclopedia.^[153]

Wikipedia's open structure inherently makes it an easy target for Internet trolls, spamming, and those with an agenda to push.^[63][154] The addition of political spin to articles by organizations including members of the US House of Representatives and special interest groups^[27] has been noted,^[155] and organizations such as Microsoft have offered financial incentives to work on certain articles.^[156] These issues have been parodied, notably by Stephen Colbert in The Colbert Report.^[157] 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.^[158]

Quality of writing[link]

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.^[159] 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."^[159]

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."^[160] A study of cancer articles by Yaacov Lawrence of the Kimmel Cancer Center at Thomas Jefferson University found that the entries were mostly accurate, but they were written at college reading level, as opposed to the ninth grade level seen in the Physician Data Query. He said that "Wikipedia's lack of readability may reflect its varied origins and haphazard editing."^[161] The Economist argued that better-written articles tend to be more reliable: "inelegant or ranting prose usually reflects muddled thoughts and incomplete information."^[162]

Coverage of topics and systemic bias[link]

Wikipedia seeks to create a summary of all human knowledge in the form of an online encyclopedia, with each topic of knowledge covered encyclopedically in one article. Since it has terabytes of disk space, it can have far more topics than can be covered by any conventional printed encyclopedia.^[163] It also contains materials that some people may find objectionable, offensive, or pornographic (cf below). ^[164] It was made clear that this policy is not up for debate, and the policy has sometimes proved controversial. For instance, in 2008, Wikipedia rejected an online petition against the inclusion of Muhammad's depictions in its English edition, 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,^[165] Pakistan^[166] and the United Kingdom,^[167] 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:^[168]

Pie chart of Wikipedia content by subject as of January 2008^[168]

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 one 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.^[169]

Furthermore, the exact coverage of Wikipedia is under constant review by the editors, and disagreements are not uncommon (see also deletionism and inclusionism).^[170][171]

As of September 2009^[update], Wikipedia articles cover 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.^[172]

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 the coverage is the reflection of the demography of the editors, which predominantly consists of young male with high educations in the developed world (cf. above)^[51]

A "selection bias"^[173] 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. Founder Jimmy Wales has noted the dangers of bias on controversial political topics or polarizing public figures.^[20]

Citing Wikipedia[link]

The crowdsourced nature of Wikipedia's content creation means that anyone can add falsehoods to, or vandalize, the site. However, it also enables people to easily reverse such actions.

Most university lecturers discourage students from citing any encyclopedia in academic work, preferring primary sources;^[174] some specifically prohibit Wikipedia citations.^[175][176] Co-founder Jimmy Wales stresses that encyclopedias of any type are not usually appropriate to use as citeable sources, and should not be relied upon as authoritative.^[177]

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.^[178] In June 2007 former president of the American Library Association Michael Gorman condemned Wikipedia, along with Google,^[179] 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." He also said that "a generation of intellectual sluggards incapable of moving beyond the Internet" was being produced at universities. He complains that the web-based sources are discouraging students from learning from the more rare texts which are found only on paper or subscription-only web sites. In the same article Jenny Fry (a research fellow at the Oxford Internet Institute) commented on academics who cite Wikipedia, saying that: "You cannot say children are intellectually lazy because they are using the Internet when academics are using search engines in their research. The difference is that they have more experience of being critical about what is retrieved and whether it is authoritative. Children need to be told how to use the Internet in a critical and appropriate way."^[179]

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."^[180]

Wales once said he receives about ten e-mails weekly from students saying they got failing grades on papers because they cited Wikipedia. According to The Sunday Times of London, Wales told the students they got what they deserved. "For God's sake, you're in college; don't cite the encyclopedia", he said.^[181]

Explicit content[link]

Wikipedia has been criticized for allowing information of graphic content. Articles depicting arguably objectionable content (such as feces, corpses, the human penis or vulva) contain graphic pictures and detailed information easily available to anyone with 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.

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,^[182] to the Internet Watch Foundation (IWF) which issues a stop list to ISPs. IWF, a nonprofit, nongovernment-affiliated organization, later criticized the inclusion of the picture as "distasteful."^[183]

In April 2010, Larry 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 U.S. federal obscenity law.^[184] 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.^[185] That law bans photographic child pornography and cartoon images and drawings of children that are obscene under American law.^[185] Sanger also expressed concerns about access to the images on Wikipedia in schools.^[186] Wikimedia Foundation spokesman Jay Walsh strongly rejected Sanger's accusation,^[187] saying that Wikipedia did not have "material we would deem to be illegal. If we did, we would remove it."^[187] Following the complaint by Larry 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."^[188]

Operation[link]

Wikimedia Foundation and the Wikimedia chapters[link]

Wikimedia Foundation logo

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 chapters, local associations of users and supporters of the Wikimedia projects, also participate in the promotion, development, and funding of the project.

Software and hardware[link]

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.^[189] 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^[190] to extend the functionality of MediaWiki software. In April 2005 a Lucene extension^[191][192] 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,^[193] which is written in Java and based on Lucene library 2.3.^[194]

Overview of system architecture, December 2010. See server layout diagrams on Meta-Wiki.

Wikipedia receives between 25,000 and 60,000 page requests per second, depending on time of day.^[195] Page requests are first passed to a front-end layer of Squid caching servers.^[196] Further statistics are available based on a publicly available 3-months Wikipedia access trace.^[197] 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),^[198][199] with a few OpenSolaris machines for ZFS. As of December 2009, there were 300 in Florida and 44 in Amsterdam.^[200]

Access to content[link]

Content licensing[link]

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,^[201] 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.^[202] Because the two licenses, GFDL and Creative Commons, were incompatible, following the request of the project, in November 2008, the Free Software Foundation (FSF) released a new version of GFDL designed specifically to allow Wikipedia to relicense its content to CC BY-SA 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.^{[203][204][205][206]}

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 due to 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.

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.^[207][208]

Methods of access[link]

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.

• Web sites – 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 Apple iOS devices (see Wikipedia iOS 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)^[209] 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.^[210][211] The Polish-language version contains nearly 240,000 articles.^[212] There are German and Spanish-language versions as well.^[213][214] 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.^[215] 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.^[216][217] 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.^[218]
• Semantic Web – The website DBpedia, begun in 2007, is a project that extracts data from the infoboxes and category declarations of the English-language Wikipedia and makes it available in a queriable semantic format, RDF. The possibility has also been raised to have Wikipedia export its data directly in a semantic format, possibly by using theSemantic MediaWiki extension. Such an export of data could also help Wikipedia reuse its own data, both between articles on the same language Wikipedia and between different language Wikipedias.^[219]

Obtaining the full contents of Wikipedia for reuse presents challenges, since direct cloning via a web crawler is discouraged.^[220] Wikipedia publishes "dumps" of its contents, but these are text-only; as of 2007 there is no dump available of Wikipedia's images.^[221]

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%.^[222]

[edit] Mobile access

See also: Help:Mobile access

Wikipedia's original medium was for users to read and edit content using any standard web browser through a fixed internet connection. In addition, Wikipedia content is now accessible through the mobile web.

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,^[223] located at en.m.wikipedia.org, which caters to more advanced mobile devices such as the iPhone, Android-based devices, or the Palm Pre. 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 Wikipedia:Metadata), such as geoinformation.^[224][225]

Impact[link]

Sister projects - Wikimedia[link]

Wikipedia has also spawned several sister projects, which are also wikis run by the Wikimedia Foundation. The first, "In Memoriam: September 11 Wiki,"^[226] created in October 2002,^[227] detailed the September 11 attacks; this project was closed in October 2006.^{[citation needed]} Wiktionary, a dictionary project, was launched in December 2002;^[228] Wikiquote, a collection of quotations, 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.^[229] Of these, only Commons has had success comparable to that of Wikipedia. Another sister project of Wikipedia, Wikispecies, is a catalogue of species.

Impact on publishing[link]

Some observers have stated that Wikipedia represents an economic threat to publishers of traditional encyclopedias, who may be 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."^[230] 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.^[231]

Cultural significance[link]

In addition to logistic growth in the number of its articles,^[232] Wikipedia has steadily gained status as a general reference website since its inception in 2001.^[233] According to Alexa and comScore, Wikipedia is among the ten most visited websites worldwide.^[9][234] The growth of Wikipedia has been fueled by its dominant position in Google search results;^[235] about 50% of search engine traffic to Wikipedia comes from Google,^[236] a good portion of which is related to academic research.^[237] The number of readers of Wikipedia worldwide reached 365 million at the end of 2009.^[10] The Pew Internet and American Life project found that one third of US Internet users consulted Wikipedia.^[238] In October 2006, the site was estimated to have a hypothetical market value of $580 million if it ran advertisements.^[239]

Wikipedia's content has also been used in academic studies, books, conferences, and court cases.^{[240][241][242]} 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.^[243] The encyclopedia's assertions are increasingly used as a source by organizations such as the U.S. Federal Courts and the World Intellectual Property Organization^[244] – though mainly for supporting information rather than information decisive to a case.^[245] Content appearing on Wikipedia has also been cited as a source and referenced in some U.S. intelligence agency reports.^[246] 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.^[247]

Wikipedia has also been used as a source in journalism,^[248][249] often without attribution, and several reporters have been dismissed for plagiarizing from Wikipedia.^{[250][251][252]} In July 2007 Wikipedia was the focus of a 30-minute documentary on BBC Radio 4^[253] which argued that, with increased usage and awareness, the number of references to Wikipedia in popular culture is such that the term 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 terms as Hoovering or Coca-Cola.