<Tr> <Td> Common cause </Td> <Td> Chance cause Non-assignable cause Noise Natural pattern <P> Random effects </P> <P> Random error </P> </Td> </Tr> <Tr> <Td> Special cause </Td> <Td> Assignable cause Signal Unnatural pattern <P> Systematic effects </P> <P> Systematic error </P> </Td> </Tr> <P> Common and special causes are the two distinct origins of variation in a process, as defined in the statistical thinking and methods of Walter A. Shewhart and W. Edwards Deming . 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 philosophy of statistics and philosophy of probability, with different treatment of these issues being a classic issue of probability interpretations, being recognised and discussed as early as 1703 by Gottfried Leibniz; various alternative names have been used over the years . </P>

Who is credited for creating a distinction between common and special cases of variation