Wikidata:Verifiability

Wikidata is not a database that stores facts about the world, but a secondary knowledge base that collects and links to references to such knowledge. This means that Wikidata does not state what the population of Germany actually is; it simply provides the information on what the population of Germany is according to a specific source, such as The World Factbook (Q11191).

Verifiability in practice

Content in the Wikidata main namespace should be verifiable, meaning supported by authoritative sources of information. In practice, this means that all statements added to Wikidata should include a reference. References are added to item pages and used to point to specific sources that back up the data provided in a statement. For more information on adding references and using sources, please see Help:Sources.

For exceptions to this rule, see Help:Sources/Items not needing sources.

Responsibility for providing sources

The burden to demonstrate verifiability lies with the editor who adds, changes, or restores statements on Wikidata. Providing a source for your edits is the best insurance against having your contributions removed.

If you are unsure how to add a source and/or are having difficulty tracking down a valid source for a particular statement, please request help on the Project Chat page, over live chat, or by e-mailing info[at]wikidata[dot]org.

Authoritative sources

Authoritative sources refers to sources of information that are deemed trustworthy, up-to-date, and free of bias for supporting a particular statement on Wikidata.

Authoritative sources of information include:

• books (novels, textbooks, encyclopedias, atlases, guidebooks, etc.)
• academic, scientific, and industry publications (journal articles, theses, dissertations, trade magazines, conference proceedings, etc.)
• news sources (newspaper articles, radio and television news broadcasts, etc.)
• policy and legislation (including government and international organization reports)
• media (radio and television scripted series, movies, songs and music recordings, etc.)

Web pages and online resources such as databases can also be authoritative sources of information. However, take care that when adding information from a database to ensure that is in fact the database that is the source of the information. This is important because some databases, particularly academic databases, only facilitate access to information (by indexing journals and other publications); likely a journal article is the actual source of information you want. More information on adding journal articles as sources can be found here. An example of when a database is an appropriate source of information is also provided.

With regards to determining what web content qualifies as an authoritative source of information, it's recommended to follow the guidelines outlined by Wikipedia for using questionable and self-published sources.

Web pages clearly published by government agencies, companies, or organizations can often be considered reliable sources of information. Web pages with unknown authors (or authors with little to no credibility) should be avoided as sources of information. Self-published information (for example, personal blogs) are acceptable sources of information when they are used to support statements about their authors and the information is clearly not self-serving. For more information, please refer to the RFC on Wikidata contributions and conflicts of interest at Wikidata:Requests_for_comment/Conflict_of_Interest.

Sources that are not usually authoritative

For a source of information to be considered authoritative, it must be possible to feasibly confirm the information of the source. For example, while every Wikidata contributor may not have (digital or physical) access to a specific newspaper article included as a source for a given statement, it might still be possible for some Wikidata contributors to track down the article and confirm the source firsthand. In practice, what this means is that most unpublished or unrecorded material cannot be used to support Wikidata content and, consequently, is not considered authoritative information.

Finding sources

Tools

While work is underway to develop a Primary sources tool, presently there are few gadgets and scripts available to Wikidata contributors that support the task of easily finding and adding sources.

The special page, Book sources provides a search for book sources by ISBN (International Standard Book Number). Enter a particular ISBN and the page will provide links to catalogues of libraries, databases, and other sites with more information about the book.

Strategies

• Assuming a Wikipedia page already exists for the item you are editing or adding to, keep in mind that in most cases it is not appropriate to cite the corresponding Wikipedia page (or pages on other Wikimedia projects) as a source of information for a Wikidata item. However, this does not mean the Wikipedia page is not useful when finding and adding sources; likely the page includes links to authoritative sources such as books, academic publications, and newspaper articles in its "References", "Notes", "Further Reading", and "External Links" sections. These sections are good starting points for locating sources to use on Wikidata.
• Try searching some of the popular resources used by the Wikipedia community and included in Wikipedia's Find source template: Google, Google News, Google Newspapers, Google Books, Google Scholar, and JSTOR.
• Check out the Wikipedia Library's list of free and authoritative information sources on the web.

Using qualifiers

Qualifiers also play a large role in ensuring content on Wikidata is verifiable, particularly in cases when a simple statement (meaning a single property-value pair) would not adequately express the knowledge to be stored about an item. Qualifiers are helpful in such cases; they can modify what an item means ("France - excluding Adélie Land"), indicate how the value of a property was determined ("Population - method estimation") and constrain the validity of the value ("Population - as of 2011").

Qualifiers therefore contribute to Wikidata's flexibility as a platform and its ability to support a plurality of perspectives, including data which may provide contradicting information. In case of disputes, community consensus ultimately determines the value of a property, however other points of views can be added as additional values using qualifiers as well as sources. Please note that just as Wikipedia does not publish original research or content representing the beliefs of its editors, Wikidata does not allow contributions that reflect personal stances or opinions, nor does it tolerate edit warring over statement values.

For more information on adding and using qualifiers, please see Help:Qualifiers.

Verifiability and copyright

Use of quotations

The quotation (P1683) property is used when adding verifiable information; specifically, it is used to provide further details or context about a source. This property replaces P387, which is now obsolete.

We look to another Wikimedia Foundation project, Wikiquote, for guidance on avoiding copyright infringement and establishing limits on quotations:

The P387 property was configured so that it only accepted string values of less than 200 characters. This is well below Wikiquote's recommendations for a maximum of 250 words per quote. Additionally, Wikiquote outlines a maximum amount of quotations that can be taken from books, films, speeches, and other sources of information. These limits vary but follow a general rule of thumb: do not take too many quotations from any one source. This rule is intended to ensure that, overall, a "fair" amount of a work is used which is not considered as copyright infringement.

In the context of Wikidata, this means that if and when quotes are used for a given item, they should come from a variety of sources, or, at least not come from the same source multiple times on one page. For example, when editing the page on a celebrity or a politician, only use one, and no more than one, quotation from the celebrity or politician's autobiography. This limit only applies to quotations, and not the actual source of information. It is perfectly appropriate to reference the same source of information multiple times on a page as needed.

Verifiability and other Wikidata policies

Notability

Verifiability of data does not guarantee inclusion on Wikidata. For these types of decisions, as well inclusion and exclusion criteria for Wikidata, see the the policy notability.