Common cause variation is normally a result of:

Common cause variation refers to the inherent variability in a process that arises from the system itself. This type of variation is typically expected and is a product of the design and overall functioning of the process. Factors contributing to common cause variation include the process materials, the methods employed, the environmental conditions, and the characteristics of the equipment used.

When a process is well-designed and operated within its natural limits, common cause variation will be present due to the normal operation of the system. This means that variations are not due to specific or unusual occurrences but are instead an integral part of how the process functions regularly.

In contrast, other options like temporary external factors, manual errors, and equipment malfunctions typically lead to special cause variation. These are specific occurrences that could skew the process performance, requiring investigation and potential corrective actions. Understanding the distinction between common cause and special cause variation is essential for effective quality management and improvement processes.