What does it mean for a process to be “in control” in Six Sigma?

For a process to be considered “in control” in Six Sigma, it means that the process is stable and only common causes of variation are present. This indicates that any fluctuations observed in the process are regular and predictable, arising from inherent characteristics of the process itself rather than from external factors or special causes that could indicate a problem.

When a process is in control, it signifies that it is functioning within predetermined limits and that the variations that do occur are normal operational variations that the system is capable of handling effectively. This state of control is essential for consistent performance, and it allows for better predictability and reliability in outputs.

Other options describe beneficial outcomes or conditions but do not accurately encapsulate the definition of being “in control.” Meeting customer needs without variations suggests a state of perfection that is rarely achievable in practical scenarios. Achieving a desired outcome reflects effectiveness but does not confirm the consistency or stability of the process. Operating at maximum efficiency suggests optimization, but it does not necessarily correlate with stable process behavior. Therefore, the defining characteristic of a process being in control is the absence of special cause variations and the predominance of common cause variations.