Expert answer in March issue

The answer to the question is almost infallible, but contains, unfortunately, one inaccuracy. The first takeaway starts with the phrase: “If the Cpk and Ppk values are equal or nearly equal, the process is in statistical control”. This assertion is wrong. The reverse phrase is true: if the process is in a state of statistical control, the values of standard deviation within and between subgroups will be close to each other. The close values, however, do not mean that the process is stable. All other takeaways are good.