A variation resulting from typical fluctuations within the system. Every system will have some amount of variation of results. The way to improve common cause variation is to change the system. The two most common mistakes that are made in reducing, understanding, or treating variation is treating a common cause as special and a special cause as common. Common Cause Variation is hard to link to any particular source whereas Special Cause Variation can be assigned to an identifiable source. Common Cause Variation is also the variation that occurs in and around a nominal task time also known as Statistical Fluctuation.
(see also Special Cause Variation)
Other Definitions
Common-cause variation: Random variation within the capability of the system. Treating common cause variation as special cause variation degrades system performance.(Advanced Projects Institute TQM Dictionary)
Common Cause Variation –
Common Cause Variation is fluctuation caused by unknown factors resulting in a steady but random distribution of output around the average of the data. It is a measure of the process potential, or how well the process can perform when special cause variation removed.
Common cause variability is a source of variation caused by unknown factors that result in a steady but random distribution of output around the average of the data. Common cause variation is a measure of the process’s potential, or how well the process can perform when special cause variation is removed. Therefore, it is a measure of the process technology. Common cause variation is also called random variation, noise, non-controllable variation, within-group variation, or inherent variation. Example: Many X’s with a small impact. (iSixSigma.com dictionary)
(see also Special Cause Variation)
