In order to measure the capability of a process, what must the process be?

To measure the capability of a process accurately, it is essential for the process to be in control. This means that the process operates consistently within established limits, free from special cause variation, allowing for a reliable assessment of its performance. When a process is in control, it behaves predictably, which enables analysts to use statistical methods to evaluate how well the process meets its specifications or quality standards.

When a process is not in control, external factors can introduce variability that distorts the evaluation of the process capability. In such cases, any measurement taken may not reflect the true performance of the process, leading to misleading conclusions about its capability. Therefore, having the process in control is a critical prerequisite for effectively measuring its capabilities.