Normality And the Process Behavior Chart

Normality is not a prerequisite for a process behavior chart or an unavoidable consequence of a predictable process. This first careful and complete examination of the relationship between the normal distribution and the process behavior chart clears up much of the confusion surrounding this subject, and it will help you overcome the superstitions that have hampered the effective use of this valuable tool. Topics include: the history of the normal distribution and early attempts to use it to analyze data; the shortcomings of procedures that check for goodness of fit; how to really compute parts-per-million defect rates; the fundamental difference between theory and practice; the relationship between R&D and SPC; the linkage between the normal distribution and basic constants in chart formulas; how non-normal distributions affect these basic constants; how three sigma limits work with over 1100 different probability models; the shortcomings of average run lengths as a tool for sensitivity analysis.