Explain if the following processes are stable or not

1. How do you tell if a process is stable or not?
2. What is a stable process in Six Sigma?
3. When would you say that a process is stable and capable?
4. Why is a stable process important?

How do you tell if a process is stable or not?

A process is said to be stable when all of the response parameters that we use to measure the process have both constant means and constant variances over time, and also have a constant distribution. This is equivalent to our earlier definition of controlled variation.

What is a stable process in Six Sigma?

A stable process can be defined as one where its variation is a result of the common cause variation of the system. The variation is due to the combination of the unique process elements and not a single identifiable special cause. This process will be steady and predictable within some expected range of variation.

When would you say that a process is stable and capable?

A stable process will rarely have outliers or unusual output values. Capable Process is a process where the observed variation is largely within the specification limits or in other words has minimal rejections. Such a process almost always produces as per customer requirements.

Why is a stable process important?

Without a stable process, you are not able to predict the performance of the process when there is a special cause variation. A special cause variation is an indicator of a significant disturbance in the process. When you monitor stability, you can catch these variations and improve your process.