Is due to a factor that has "slipped" into the process causing unstable or unpredictable variation.
Are unpredictable variations that are abnormal to the process including human error, equipment failure, defective/changed raw materials, acid spills, power failures, etc.; failure to remove them can result is corrosion, scale, metal fatigue, lower equipme
Removal of all special causes of variation yields a process that is in statistical control.
Correctable by local personnel.
Common Causes of Variation
Account for 85-95% of quality problems
Are due to the many small sources of variation "engineered" into the process of the "system”.
Are naturally caused and are always present in the process because they are linked to the system's base ability to perform; it is the predictable and stable inherent variability resulting from the process operating as it was designed.
Standard deviation, s, is used as a measure of the inherent process variability; it helps describe the well-known normal distribution curve.
Correctable only by management; typically requires the repair/replacement of a system's component, or the system itself.
