In a quality process, what is indicated by control limits?

Control limits are statistical boundaries set on control charts that represent the expected variations of a process. They are calculated based on the data collected from the process and are used to determine whether a process is in a state of control or if there are indications of variability that may require attention.

When control limits are established, they reflect the natural variability inherent in the process. The region within these limits signifies where the process output is expected to fall most of the time, specifically within a defined percentage (typically 95% or 99%) based on statistical principles. Any points that fall outside these control limits indicate that the process may be experiencing special cause variation, which could suggest issues that need to be investigated.

Thus, control limits effectively indicate the acceptable variance in a process. This allows quality professionals to monitor and ensure that the process remains stable and produce outputs that meet quality specifications. Recognizing what constitutes acceptable variation is key to maintaining high-quality standards and process improvement initiatives.