| Assignable
Cause Variation |
|
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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