In a control chart, what does a control limit represent?

In a control chart, a control limit represents the acceptable range for process variation. Control limits are statistically determined boundaries that help you understand the expected variability within a process. Specifically, they are derived from the mean and standard deviation of the process data and provide a framework for evaluating whether a process is in a state of statistical control.

When data points fall within the control limits, it indicates that the process variation is normal and consistent, suggesting that any changes in data points are due to common cause variation rather than special cause variation. Conversely, if data points fall outside the control limits, it triggers further investigation, as this suggests that there may be an underlying issue that requires corrective action.

This definition reinforces the importance of control limits in quality improvement initiatives, as they guide decision-making about process stability and capability. Focusing on the control limits helps organizations monitor processes effectively and take proactive steps to maintain quality.