Common Cause Variation

Common- and special-causes are the two distinct origins of variation, in a process that features in the statistical thinking and methods of Walter A. Shewhart and W. Edwards Deming. However, it can be argued that they were recognised and discussed as early as 1703 by Gottfried Leibniz and are particularly important in the thinking of economists Frank Knight, John Maynard Keynes and G. L. S. Shackle. Several alternative names have been used over the years.
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the normal random variation in output for a process.