Process Stability is a process’s ability to be consistent and predictable over a sufficiently long period of time. It describes a condition in which the process’s characteristics (e.g. average performance value, variation) tend to be constant. Such a process becomes consistent with performance levels set before the process’s start.
A stable process is always consistent with its performance objectives and also ready for improvements. Stability ensures process predictability and alignment. If the process is unstable, it is performed out of control. It tends to be unpredictable because of random variations that do not correlate with normal or standard distribution.
Charting is an analytical tool that is often used in assessing and visualizing process stability. For example, Scatter chart shows a sufficient number of performance indicators of a process collected over a long period to display random variation and normal distribution. The graph includes a variation line that helps track process changes and figure out instances when the process becomes unstable. Charting also provides input data for process analysis and performance improvement.