ABSTRACT
Statistical process control (SPC) is an application of statistics to manufacturing processes. SPC provides evidence that feeds back information to the process manager that something has changed, relative to normal variation. Control action based on normal noise is both unnecessary and unwanted. Trends in overall level, sudden shifts in level, cycling in level, and changes in variability all indicate the presence of an assignable cause. For instance, an online gas chromatograph may be sampling the products of several distillation columns. Many processes use product attributes to measure whether a product conforms or does not conform to specifications. This chapter presented the fundamental statistical analysis of SPC (or six sigma, or quality control methods). After an assignable cause is recognized, the important tasks of trouble shooting, rational diagnosis, and decision making need to be performed.
