Common causes of variation

Within any process there are many variable factors (such as wind and muscle tremors in firing a gun) each of which may vary a small amount and in a predictable way, but when taken together result in a degree of randomness in the output, as indicated in the figure below. These seemingly uncontrollable factors are called common causes of variation.

Common causes of variation cannot be eliminated by reacting to individual variations. The spread in results can only be reduced through a deep understanding of how the process works.

Control Charts can be used to differentiate between common and special causes of variation.

See also:

Toolbook chapter: Variation