Wikipedia:Verifiability

To discuss particular sources, see the reliable sources noticeboard. For vandalism, see WP:VAND.

The threshold for inclusion in Wikipedia is verifiability, not truth—whether readers can check that material in Wikipedia has already been published by a reliable source, not whether editors think it is true.

All material in Wikipedia articles must be attributable to a reliable published source to show that it is not original research, but in practice not everything need actually be attributed. This policy requires that all quotations and any material challenged or likely to be challenged be attributed to a reliable, published source in the form of an inline citation, and that the source directly support the material in question. This is strictly applied to all material in the mainspace—articles, lists, sections of articles, and captions—without exception, and in particular to material about living persons. Anything that requires but lacks a source may be removed, and unsourced contentious material about living persons must be removed immediately. For how to write citations, see Citing sources.

Verifiability is one of Wikipedia's core content policies, along with No original research and Neutral point of view. These policies jointly determine the type and quality of material that is acceptable in articles. They should not be interpreted in isolation from one another, and editors should familiarize themselves with all three.

Reliable sources and other principles

Reliable sources and notability

Further information: Wikipedia:Notability

If no reliable third-party sources can be found on a topic, Wikipedia should not have an article on it.

Reliable sources and neutrality

Further information: Wikipedia:Neutral point of view

All articles must adhere to the Neutral point of view policy (NPOV) fairly representing all majority and significant-minority viewpoints that have been published by reliable sources, in rough proportion to the prominence of each view. Tiny-minority views need not be included, except in articles devoted to them. Where there is disagreement between sources, use in-text attribution: "John Smith argues that X, while Paul Jones maintains that Y," followed by an inline citation.

Reliable sources and original research

Further information: Wikipedia:No original research

The No original research policy (NOR) has three requirements relevant to the Verifiability policy:

1. All material in Wikipedia articles must be attributable to a reliable published source. This means that a source must exist for it, whether or not it is cited in the article. Wikipedia must never be a first publisher.
2. Sources must support the material clearly and directly: drawing inferences from multiple sources to advance a novel position—called original synthesis, or original SYN—is prohibited by the NOR policy.
3. Articles should be based largely on reliable secondary sources. While primary sources are normally welcome, there are dangers in relying on them. For more information, see the Primary, secondary, and tertiary sources section of the NOR policy, and the Misuse of primary sources section of the BLP policy.

When a reliable source is required

Anything challenged or likely to be challenged

This policy requires that all quotations and any material challenged or likely to be challenged be attributed to a reliable published source using an inline citation. The source should be cited clearly and precisely, with page numbers where appropriate.

Burden of evidence

The burden of evidence lies with the editor who adds or restores material. Any material lacking a reliable source directly supporting it may be removed. How quickly this should happen depends on the material and the overall state of the article. Editors might object if you remove material without giving them time to provide references. It has always been good practice to make reasonable efforts to find sources yourself that support such material, and cite them. Do not leave unsourced or poorly sourced material in an article if it might damage the reputation of living persons or organizations, and do not move it to the talk page.

Reliable sources

REFERENCES

1. Marić R., Radojković Z., Šegović D., Pavlović A. Parturition as risk factor for the apperance of intrahospital infections. Giornale di malattie infettive e parassitarie, 1990; 42 (7) :536-8.

2. Milenkovic D., Radosavljevic N., Radosavljevic Z., Jovic S., Cobeljic R., Djordjevic O., Stojanovic A., Pavlovic A., Perisic D. Correlation of bone mineral density and fractures in postmenopausal female patients. In: IOF World Congress on osteoporosis and Tenth European Congress on Clinical and Economic Aspects of Osteoporosis and Osteoarthritis: abstract book, Florence, Italy, 2010, 230.

3. Pavlović A., Milovanovic N. The possibilities of pulsing electromagnetic field in treatment of patients with traumatic peroneal nerve laesions. In: 5th World Congress of International Society of Physical and Rehabilitation Medicine: abstract book, Istanbul, Turkey, 2009, 603.

4. Pavlović A., Milovanovic N. The possibilities of pulsing electromagnetic field in treatment of patients with hip joint osteoarthritis. In: 7th Mediterranean Congress of Physical and Rehabilitation Medicine: book of abstracts, Portorož, Slovenia, 2008, 283.

5. Pavlović A., Milovanovic N. Effects of electromagnetic field in treatment od patients with fracture of distal part of radius. In: 6th Mediterranean Congress of PRM: abstract book, Vilamoura, Algavre, Portugal, 2006, 139.

6. Pavlović A. The effects of pulsing electromagnetic field in treatment of patients with traumatic peroneal nerve laesions. In: 3rd World Congress of the International Society of Physical and rehabilitation Medicine – ISPRM: abstract book, Sao Paulo, Brazil, 2005.

7. Pavlović A. The effects of pulsing electromagnetic field in treatment of patients with hip joint osteoarthritis. In: 4th ISPO Central&Eastern European Conference and 5th Congress of Serbia & Montenegro Physiatrists: Proceedings, Belgrade, 2005, 90.

8.Pavlović A. The effects of special techniques of oscillatory and sliding passive movements in treatment of patients with knee joint arthrosis. In: 14th European Congress of Physical and Rehabilitation Medicine: abstract book, Vienna, Austria, 2004, 99.

9.Pavlović A. Therapeutic possibilities of electromagnetic field in treating of patients with knee injuries. In: 2nd World Congress of the International Society of Physical and Rehabilitation Medicine: abstract book, Prague, Czech Republic, 2003, 197.

10. Pavlović A., Rakočević A. The therapeutic possibilities of high frequency pulsed electromagnetic field in treating of patients with atherosclerosis obliterans of lower limbs. In: 12th European Congress of Physical Medicine & Rehabilitation: abstract book, Antalya, Turkey, 2000, 167.

11.Pavlović A., Rakočević A. The therapeutic effects of high frequency pulsed electromagnetic field in treating of patients with Burger’s disease. In: 12th European Congress of Physical Medicine & Rehabilitation: abstract book, Antalya, Turkey, 2000, 167.

12.Rakočević A., Pavlović A. The therapeutic effects of low frequency electromagnetic field in treating of patients with epicondylitis lateralis humeri. In: 12th European Congress of Physical Medicine & Rehabilitation: abstract book, Antalya, Turkey, 2000, 89.

13.Pavlović A. Therapeutic possibilities of high frequency pulsed electromagnetic field in treating patients with atherosclerosis obliterans of lower limbs. In: 13th World Con- gress of the International Federation of Physical Medicine and Rehabilitation: Acade- my annual assembly abstracts, Washington, USA, 1999, 1137.

14.Pavlović A., Rakočević A., Jović S. The therapeutic effects of pulsed high frequency electromagnetic field in treating of patients with peripheral chronic obliterans arteropathies. In: II Mediterranean Congress og Physical Medicine and Rehabilitation: abstract book, Valencia, Spain, 1998, 139.

15.Pavlović A., Rakočević A. Terapijski efekti pulsirajućeg visokofrekventnog elektromagnetnog polja u tretmanu pacijenata sa Birgerovom bolešću. U: I Slovenski Kongres zdravnikov za fizikalno in rehabilitacijsko medicino: zbornik povzetkov, Bled, Slovenija, 1998, 92.

16.Pavlović A. Atrial Natriuretic Peptide (ANP) in chronic coronary disease. In: XI World Congress of Cardiology: abstract book, Philippines, 1990, 403.

17..Avramović D., Avramović K., Pavlović A., Sušić D., Kentera D., Ivanović B. Atrial Natriuretic Peptide (ANP) with patients suffering from a valvular cardiac deffect. In: XI World Congress of Cardiology: abstract book, Philippines, 1990, 402.

18.Avramović D., Pavlović A., Avramović K., Mihajlović G., Uglješić M. A 24 hours follow-up of blood pressures in normo-tensive persons from the ages of 20-30 years and from 40-50 years. In: XI World Congress of Cardiology: abstract book, Philippines, 1990, 117.

19.Avramović D., Pavlović A., Ivanović B., Pešić R., Sušić D., Kentera D., Petrović P. Atrial Natriuretic Peptide in aortic blood and the highest pressure in the right atrium. In: 4th Annual Meeting of the Mediterranean Association of Cardiology and Cardiac Surgery: abstract book, Antalya, Turkey, 1990, 175.

20.Pešić R., Avramović D., Pavlović A., Ivanović B., Petrović P. The level of Atrial Natriuretic Peptide in the right ventricle and the pressure in the right heart. In: 4th Annual Meeting of the Mediterranean Association of Cardiology and Cardiac Surgery: abstract book, Antalya, Turkey, 1990, 245.

21.Zečević M., Avramović D., Pantić J., Bukmirović V., Ivanović B., Jeremić O., Pavlović A. Prognostic significance of myocardial contusion in patients with multi-systemic trauma. In: 4th Annual Meeting of the Mediterranean Association of Cardiology and Cardiac Surgery: abstract book, Antalya, Turkey, 1990, 181.

22.Marić R., Ristić S., Babić ., Pavlović A. Secondary prevention of rheumatic arthritis as the condition for the favorable prognosis of the disease. In: Rheumatologic Conference with international participation: abstract book, Trenčianske Teplice, Czechoslovakia, 1988.

23.Marić R., Kastratović B., Pavlović A. Descriptive study of osteoarthrosis on the territory of one commune. In: East and West Combined Orthopaedic Meeting: abstract book, Belgrade, 1988, 72.

24.Avramović D., Ivanović B., Stanojević M., Matic D., Pavlović S., Pavlović A., Šujeranović D. Zorkaptil u lečenju arterijske hipertenzije. U 9. Jugoslovensko-Sovjetski Medicinski Dani: zbornik rezimea, Sarajevo, 1988, 104.

25. Stanojević M., Avramović D., Ivanović B., Kalimanovska D., Pavlović S., Pavlović A., Šujeranović D. Zorkaptil u lečenju srčane insuficijencije. U: 9. Jugoslovensko-Sovjetski Medicinski Dani: zbornik rezimea, Sarajevo, 1988, 158.

Newspaper and magazine blogs

Several newspapers host columns that they call blogs. These are acceptable as sources so long as the writers are professionals and the blog is subject to the newspaper's full editorial control. In March 2010, the Press Complaints Commission in the UK ruled that journalists' blogs hosted on the websites of newspapers or magazines are subject to the same standards expected of comment pieces in that organization's print editions. Where a news organization publishes an opinion piece, the writer should be attributed (e.g. "Jane Smith has suggested..."). Posts left by readers may never be used as sources.

Sources that are usually not reliable

Questionable sources

Questionable sources are those with a poor reputation for checking the facts, or with no editorial oversight. Such sources include websites and publications expressing views that are widely acknowledged as extremist, or promotional, or which rely heavily on rumor and personal opinion. Questionable sources should be used only as sources of material on themselves, especially in articles about themselves; see below. They are generally unsuitable for citing contentious claims about third parties.

Self-published sources

Further information: Wikipedia:Biographies of living persons § Avoid self-published sources

Anyone can create a website or pay to have a book published, then claim to be an expert in a certain field. For that reason self-published media, such as books, newsletters, personal websites, open wikis, personal or group blogs, Internet forum postings, and tweets, are largely not acceptable as sources. Self-published expert sources may be considered reliable when produced by an established expert on the topic of the article whose work in the relevant field has previously been published by reliable third-party publications. Caution should be exercised when using such sources: if the information in question is really worth reporting, someone else is likely to have done so. Self-published sources should never be used as third-party sources about living persons, even if the author is an expert, or well-known professional researcher or writer.

Self-published or questionable sources as sources on themselves

Self-published and questionable sources may be used as sources of information about themselves, usually in articles about themselves or their activities, without the requirement in the case of self-published sources that they be published experts in the field, so long as:

1. the material is not unduly self-serving;
2. it does not involve claims about third parties;
3. it does not involve claims about events not directly related to the source;
4. there is no reasonable doubt as to its authenticity;
5. the article is not based primarily on such sources.

Accessibility

Access to sources

See also: Wikipedia:WikiProject Resource Exchange

Verifiability in this context means that anyone should be able to check that material in a Wikipedia article has already been published by a reliable source. The principle of verifiability implies nothing about ease of access to sources: some online sources may require payment, while some print sources may be available only in university libraries. WikiProject Resource Exchange may be able to assist in obtaining source material.

Non-English sources

Because this is the English Wikipedia, English-language sources are preferred over non-English ones, unless no English sources of equal quality and relevance are available. When quoting a source in a different language, provide both the original-language text and an English translation in the text or a footnote. Translations published by reliable sources are preferred over translations by Wikipedians. When citing such a source without quoting it, the original and its translation should be provided if requested by other editors: this can be added to a footnote or the talk page. When posting original source material, editors should be careful not to violate copyright; see the fair-use guideline.

Other issues

Tagging a sentence, section, or article

If you want to request a source for an unsourced statement, consider tagging a sentence with the {{citation needed}} template by writing {{cn}} or {{fact}}. Other templates are available here for tagging sections or entire articles. Alternatively, leave a note on the talk page requesting a source, or move the material there. To request verification that a reference supports the text, tag it with {{verification needed}}. Material that fails verification may be tagged with {{failed verification}} or removed. Unsourced or poorly sourced contentious material about living persons should be removed immediately and not tagged or moved to the talk page.

Exceptional claims require exceptional sources

See also: Wikipedia:Fringe theories

Exceptional claims require high-quality sources. Red flags that should prompt extra caution include:

• surprising or apparently important claims not covered by mainstream sources;
• reports of a statement by someone that seems out of character, or against an interest they had previously defended;
• claims that are contradicted by the prevailing view within the relevant community, or that would significantly alter mainstream assumptions, especially in science, medicine, history, politics, and biographies of living persons. This is especially true when proponents say there is a conspiracy to silence them.

Reliable sources noticeboard and WP:IRS

Further information: Wikipedia:Reliable sources noticeboard and Wikipedia:Identifying reliable sources

To discuss the reliability of a specific source for a particular statement, consult the reliable sources noticeboard, which seeks to apply this policy to particular cases. For a guideline discussing the reliability of particular types of sources, see Wikipedia:Identifying reliable sources (WP:IRS). In the case of inconsistency between this policy and the WP:IRS guideline, or any other guideline, the policy has priority.

Wikipedia and sources that mirror or use it

Articles on Wikipedia or on websites that mirror its content should not be used as sources, because this would amount to self-reference. Similarly, editors should not use sources that present material originating from Wikipedia to support that same material in Wikipedia, as this would create circular sourcing—Wikipedia citing a source that derives its material from Wikipedia. Wikipedia may be cited with caution as a primary source of information on itself, such as in articles about itself.

See also

• Wikipedia:Citation clutter, an essay
• Wikipedia:Core content policies, an essay
• Wikipedia:Identifying reliable sources (medicine), a guideline
• Wikipedia:List of free online resources
• Wikipedia:Template messages/Sources of articles
• Wikipedia:When to cite, an essay
• WikiProject Fact and Reference Check
• WikiProject Resource Exchange

Further reading

• Wales, Jimmy. "WikiEN-l insist on sources", WikiEN-l, July 19, 2006: "I really want to encourage a much stronger culture which says: it is better to have no information, than to have information like this, with no sources."