# Getting started with statistically based process improvement

Getting started with statistically based process improvement.

Let me know what you think

Thanks for sharing. A few observations:

In Step 2 you encourage determining the current state of the process through use of control charts, which is sound advice, but you also suggest that “A basic condition that must be satisfied before any improvements can be made is a stable and predictable process.” There’s a bit of redundancy there, because in this context “stable” and “predictable” are synonymous. Also, the problem might be instability, so in curing that issue, the problem might be solved. In other words, you can make improvements to an unstable process, contrary to your assertion that stability must be achieved as a prerequisite.

The charts in figures 1 and 2 show signs of instability other than points beyond the control limits; you might want to point out the fact that there is more than one test for statistical control.

You say, “Any points outside of the limits represent what are known as special causes…” Not necessarily; when using the normal curve as a model (which might not be advisable) we can predict that some points will naturally fall outside the ±3-sigma limits. It might be good to point this out, and advise against tampering.

You say, “Typically most improvement projects identify that the process is unstable which then begins the task of identifying why that is?” I’m not at all sure that the statement is true. In many cases, analysis will reveal a predictable but incapable process. Also, the sentence should end with a period and not a question mark.

You say, “If after getting you process under control the upper and/or lower control limits are outside of the specification limits you have a process that is near the brink of chaos.” Clearly, the condition you describe is undesirable in most cases, but “near the brink of chaos” seems a bit strong. Although the instances are rare, there are times when a certain level of nonconforming output is acceptable and economically necessary.

In addressing “Sustaining the Improvement,” you say, “Without the proper controls all processes will tend to work back to where they began before the project.” This is certainly true, but the object of the project should be installation and monitoring of controls. That is to say, the object should be to identify the process controls which, if maintained, will result in conforming output, and then monitor and measure those, rather than focusing on part/output measurement. The entire idea of process improvement should be making the process predictable by controlling the process variables that have been proven to contribute to conforming output.