Common cause variation is an essential concept in quality management. It refers to the inherent variability that exists in a process due to its normal operation. Common causes are part of the system and are not attributable to specific events or factors. They are the typical fluctuations that occur when a process is stable and in statistical control.
Examples of common cause variation include:
* Inherent Measurement Error: Measurement instruments inherently have some level of error or imprecision. This variation is common and expected.
* Equipment Variation: Even well-maintained equipment will exhibit some variability in its performance due to design tolerances, wear, and other factors.
* Process Variation: Processes naturally have variations in their output due to factors such as material properties, environmental conditions, and machine settings.
* Human Performance: Human operators, even when well-trained, introduce variability due to their inherent capabilities and limitations.
In contrast, special cause variation arises from specific events or factors that are not part of the normal process.
These events lead to sudden and significant changes in the process output. Special causes are typically identifiable and can be traced back to specific events or conditions.
In summary, common cause variation is the background noise of a process, while special cause variation represents unexpected disturbances. Effective quality management involves understanding and managing both types of variation to improve processes and achieve better outcomes.
References:
* ASQ Certified Manager of Quality/Organizational Excellence Handbook, Fourth Edition
* Understanding Variation
* ASQ Certified Manager of Quality/Organizational Excellence