Chance or random causes of variation, also known as common causes, are inherent in a process and cannot be easily removed. They represent the natural fluctuations that occur due to the complexity of the system.
Common causes are not caused by specific assignable factors but are part of the inherent variability of the process. Managing common cause variation requires improvements to the process itself. On the other hand, special cause variation, also known as signal cause variation, arises due to unusual circumstances and is not an inherent part of the process. Special causes can be identified and removed. The key distinction is that common causes are always present, while special causes are sporadic and unexpected. Recognizing and managing both types of variation is essential for quality improvement and process stability12. References)