sig·​ma | \ ˈsig-mə How to pronounce sigma (audio) \

Definition of sigma

1 : the 18th letter of the Greek alphabet — see Alphabet Table

Examples of sigma in a Sentence

Recent Examples on the Web Thomson and his team must reach five-sigma certainty to definitively claim a discovery. Quanta Magazine, "The Particle That Broke a Cosmic Speed Limit," 14 May 2015 Historically, most industrial companies operate between three and four sigma, making them between 93% and 99.3% defect-free (these figures can vary slightly depending on the statistical model). Oliver Staley, Quartz at Work, "Whatever happened to Six Sigma?," 3 Sep. 2019 The gold standard for discovery is a five-sigma result, comparable to tossing 21 heads in a row. Jennifer Ouellette, Quanta Magazine, "In the Hunt for Dark Matter, Promises to Keep?," 18 July 2013 Through regular reports released under the name sigma, the company offers a lens into the changing trends of the insurance world. David Grossman, Popular Mechanics, "Global Warming Is Already Costing the Insurance Industry Historic Amounts," 17 Apr. 2019 Typically, only five sigma is needed to call something a discovery. John Timmer, Ars Technica, "Visitor from another solar system accelerated away from the Sun," 28 June 2018 Physicists and astronomers, however, aren't usually convinced that two phenomena are connected until there's no more than a one in 3.5 million, or 5 sigma, probability of a coincidence. Daniel Clery, Science | AAAS, "Ghostly particle caught in polar ice ushers in new way to look at the universe," 12 July 2018 Physics requires a statistical significance of five sigma to declare discovery; MiniBooNE is tantalizingly close and will probably be there within the next two years. John Timmer, Ars Technica, "Weird neutrino excess won’t go away, hints at new physics," 8 June 2018 The MiniBooNE result had a standard deviation measured at 4.8 sigma, just shy of the 5.0 threshold physicists look for. NBC News, "A major physics experiment just detected a particle that shouldn't exist," 3 June 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'sigma.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of sigma

1584, in the meaning defined at sense 1

History and Etymology for sigma


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Time Traveler for sigma

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The first known use of sigma was in 1584

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Cite this Entry

“Sigma.” The Dictionary, Merriam-Webster Inc., Accessed 12 December 2019.

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How to pronounce sigma (audio)

English Language Learners Definition of sigma

: the 18th letter of the Greek alphabet

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a period of high artistic development

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