2. How do you know whether a deviation in product characteristics is a "normal" variation of a statistical nature, or whether it is due to a process malfunction caused by an assignable cause that needs to be corrected?

We invite you to consult the fact sheet on Statistical quality control: the concept of process centring and dispersion [FIC 0562] for :

• remind you of the concepts of statistical dispersion of values, normal distribution and dispersion represented by the standard deviation;

• review how to calculate the mean and standard deviation of a normal distribution.

In what follows, we'll assume that the distribution of the value of the product characteristic...