Statistical Thinking to Improve Quality

This posting describes the Hoerl-Snee Process-Improvement Strategy.   This strategy was originally described in Hoerl-Snee (1995), and it also appears in Britz et (2000) and Hoerl-Snee (2002).   Prior to implementing the Process Improvement Strategy, one should define the scope and objectives for the improvement effort.  The following figure displays a flowchart of the improvement strategy steps and lists some example tools to perform the corresponding steps. 

 

The figure does not show the entire process improvement flow.    Eliminating special causes involves the Problem Solving Strategy.   Future postings will describe this strategy. 

Two primary features distinguish this strategy from the DMAIC strategy.   That is,
·        Improvement occurs in iterative sequential iterative steps.  One could call this strategy an enhanced PDCA approach to improvement.
·        One of the first steps is to remove special-cause sources of variation.   One reason for this is that the problem analysis for removing special causes often differs from the analysis to reduce common-cause variation.   Common causes are always present; however, special causes operate in isolated circumstances.

Note that the resin output variation case study clearly illustrated the above features of the process improvement strategy.  Improvement occurred in sequential cycles involving planning, implementing and collecting data.   Also, the first improvement action by the resin team was to determine whether special causes were present and then to correct them.   After that they moved on to reduce the variation contributed by common causes.

References
1.     Hoerl, R. W. and R. D. Snee (1995). Redesigning the Introductory Statistics Course. Madison, Wisconsin, University of Wisconsin, Center for Quality and Productivity Improvement.
2.     Britz, G. C., D. W. Emerling, et al. (2000). Improving Performance Through Statistical Thinking. Milwaukee, WI, ASQ Quality Press.
3.     Hoerl, R. and R. D. Snee (2002). Statistical Thinking - Improving Business Performance. Pacific Grove, CA, Duxbury.