What best describes common cause variation?

Common cause variation refers to the inherent fluctuations that are part of a stable process. This type of variation arises from the design of the process itself and is predictable and consistent over time. When a process operates under normal conditions, it will produce results that exhibit this kind of variation due to the natural differences in the process elements. Understanding common cause variation is essential for quality improvement because it indicates that the process is stable and predictable, but may require a redesign if the overall performance needs enhancement.

In contrast, variation that can be eliminated through adjustment pertains to special cause variation, which comes from specific incidents or unanticipated changes in the environment. This distinction between common and special cause variation is fundamental in quality management, particularly in methods such as Six Sigma or Statistical Process Control (SPC), where the goal is to identify and eliminate sources of variation in order to improve process performance.