Sagan standard

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The Sagan standard is an aphorism which says that "extraordinary claims require extraordinary evidence" (ECREE).[1]

Applying the standard[edit]

ECREE is related to Occam's razor in the sense that according to such a heuristic, simpler explanations are preferred to more complicated ones. Only in situations where extraordinary evidence exists would an extraordinary claim be the simplest explanation.[2] A routinized form of this appears in hypothesis testing where the hypothesis that there is no evidence for the proposed phenomenon, what is known as the "null hypothesis", is preferred. The formal argument involves assigning a stronger Bayesian prior to the acceptance of the null hypothesis as opposed to its rejection.[3] How to weigh such priors requires careful consideration, and it is usually at this point that arguments between those who make extraordinary claims and those who debunk them occur.


The aphorism was made popular by astronomer Carl Sagan through the 1980 TV show Cosmos.[4] Two 1978 articles, one in U.S. News & World Report and another by Koneru Ramakrishna Rao in the Journal of Parapsychology both quote physicist Philip Abelson, then the editor of Science, using the same phrase.[5][6] In "On the Extraordinary: An Attempt at Clarification" (1978), sociologist Marcello Truzzi said "an extraordinary claim requires extraordinary proof."[7]

Others have put forward very similar ideas with different phrasing. Théodore Flournoy, in 1899, put forward the principle that "the weight of evidence for an extraordinary claim must be proportioned to its strangeness",[8] attributing the idea to Laplace, whom he quotes saying, in 1814, that "we ought to examine [seemingly inexplicable phenomena] with an attention all the more scrupulous as it appears more difficult to admit them".[9] In 1808, Thomas Jefferson also said "A thousand phenomena present themselves daily which we cannot explain, but where facts are suggested, bearing no analogy with the laws of nature as yet known to us, their verity needs proofs proportioned to their difficulty."[10]

In 2004 the cyclist Lance Armstrong used the phrase "Extraordinary allegations require extraordinary evidence" to discredit allegations of doping put to him by journalist David Walsh.[11] Armstrong was later asked "What is it about you that makes ordinary proof insufficient to bring you down? For murderers, we're not looking for extraordinary proof, we're looking for proof. But you're saying it must be extraordinary. Why?".[12] Armstrong later confessed to doping in 2013.[13]

See also[edit]


  1. ^ Kaufman, Marc (2012). First Contact: Scientific Breakthroughs in the Hunt for Life Beyond Earth (Reprint ed.). Simon and Schuster. p. 124. ISBN 978-1439109014.
  2. ^ Smith, Jonathan C. (2011). Pseudoscience and Extraordinary Claims of the Paranormal: A Critical Thinker's Toolkit. John Wiley & Sons. ISBN 1444358944.
  3. ^ Matthews, Paul (2010). Sample Size Calculations: Practical Methods for Engineers and Scientists. Mathews Malnar and Bailey. p. 6. ISBN 0615324614.
  4. ^ Sagan, Carl (December 14, 1980). "Encyclopaedia Galactica". Cosmos: A Personal Voyage. Episode 12. 01:24 minutes in. PBS.
  5. ^ "A Stepchild of Science Starts to Win Friends". U.S. News & World Report. 1978-07-31. pp. 41–42. Retrieved 2017-10-14. Philip H. Abelson, editor of the authoritative journal Science, agrees that parapsychological research has improved markedly, but he is dubious about the results. "These extraordinary claims require extraordinary evidence," he contends.
  6. ^ Rao, K.R., 1978, Psi: Its place in nature. Journal of Parapsychology vol 42.
  7. ^ Marcello Truzzi, "On the Extraordinary: An Attempt at Clarification", Zetetic Scholar, Vol. 1, No. 1, p. 11, 1978.
  8. ^ Flournoy, Théodore (1899). Des Indes à la planète Mars: étude sur un cas de somnambulisme avec glossolalie. Slatkine. pp. 344–345. ISBN 9782051004992.*Flournoy, Théodore (2007). From India to the Planet Mars: A Study of a Case of Somnambulism. Daniel D. Vermilye, trans. Cosimo, Inc. pp. 369–370. ISBN 9781602063570.
  9. ^ Laplace, Pierre-Simon de (1825). Essai philosophique sur les Probabilités (in French) (5th ed.). pp. 134–135. Retrieved 6 July 2019.
  10. ^ Berkes, Anna (November 14, 2008). "Who is the liar now?". Thomas Jefferson Foundation. Retrieved October 29, 2016. Letter to Daniel Salmon on 15 February 1808 discussing the nature and origin of meteorites. U.S. Library of Congress image
  11. ^ Fotheringham, William (24 August 2012). "Lance Armstrong shying away from a fight is an extraordinary moment - William Fotheringham" – via
  12. ^ Chappell, Matt. "The State Of Doping In Sport In 2015, By David Walsh". AskMen.
  13. ^ Carter, Chelsea J. "Lance Armstrong facing lifetime ban, loss of titles". CNN.