What are control limits in a control chart?

Control limits in a control chart represent the boundaries of acceptable process variation. These limits are established based on the statistical properties of the process, typically calculated using historical data. The upper control limit and the lower control limit are determined through the means and standard deviations of the process data, providing a range within which the process variation is expected to occur if it is stable and in control.

When variations in the process fall within these control limits, it indicates that the process is operating normally, adhering to its inherent variability. Conversely, when data points fall outside these limits, it signals that there may be special cause variations affecting the process, warranting further investigation to determine the root cause and implement corrective actions if necessary.

This concept is crucial for maintaining quality and consistency in processes, as it helps in monitoring the stability and predictability of performance over time. The other options, while related to process analysis, do not accurately describe the specific function of control limits in a control chart.