| Assignable Cause Variation |
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Synonym for Special Cause Variation
The sources of variation in a process that are truly random. They usually conform to a normal distribution, or a distribution that is closely related to the normal distribution.
Common cause variation is inherent in the process and can only be reduced by changes to the system; typically management action. See also 'Special Cause Variation'
Synonym for Common Cause Variation
See Plan Do Check Act
A synonym for Plan Do Study Act
A cycle for process improvement projects suggested by Shewhart (see Plan Do Study Act).
A cycle for process improvement projects suggested by J Edwards Deming. Based on the original Plan Do Check Act cycle suggested by Shewhart:
| Plan: |
Develop a plan for improving the quality of a process |
| Do: |
Execute the plan on a prototype scale |
| Study: |
Evaluate Feedback and adjust or confirm the plan |
| Act: |
Build the plan into the system |
Special Cause Variation is caused by factors that are non-random. Special causes can be identified and removed from the process.
Processes that contain special cause variation are not stable, or capable, and cannot be effectively monitored using control charts. The main purpose of control charts is the timely identification of special causes so that they can be eliminated. See also 'Common Cause Variation'.
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