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Common cause and special cause (statistics)
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<table><tbody><tr><th>Type of variation</th><th>Synonyms</th></tr><tr><td>Common cause</td><td>Chance causeNon-assignable causeNoiseNatural pattern<p>Random effects</p><p>Random error</p></td></tr><tr><td>Special cause</td><td>Assignable causeSignalUnnatural pattern<p>Systematic effects</p><p>Systematic error</p></td></tr></tbody></table> <p>Common and special causes are the two distinct origins of variation in a process, as defined in the <a href="/facts/Statistical_thinking/HfokKQnX">statistical thinking</a> and methods of <a href="/facts/Walter_A._Shewhart/7rE37orq">Walter A. Shewhart</a> and <a href="/facts/W._Edwards_Deming/ytaxg6sv">W. Edwards Deming</a>. Briefly, "common causes", also called natural patterns, are the usual, historical, quantifiable variation in a system, while "special causes" are unusual, not previously observed, non-quantifiable variation. </p><p>The distinction is fundamental in <a href="/facts/Philosophy_of_statistics/Wok6XV4Q">philosophy of statistics</a> and <a href="/facts/Philosophy_of_probability/qmuEgkIU">philosophy of probability</a>, with different treatment of these issues being a classic issue of <a href="/facts/Probability_interpretations/qmuEgkIU">probability interpretations</a>, being recognised and discussed as early as 1703 by <a href="/facts/Gottfried_Leibniz/cTc2er83">Gottfried Leibniz</a>; various alternative names have been used over the years. The distinction has been particularly important in the thinking of economists <a href="/facts/Frank_Knight/p54aNVR5">Frank Knight</a>, <a href="/facts/John_Maynard_Keynes/4otHjBRu">John Maynard Keynes</a> and <a href="/facts/G._L._S._Shackle/d77IGbPK">G. L. S. Shackle</a>. </p>