Statistical Thinking to Improve Quality

Statistical Thinking gives a framework for learning and action to improve performance.  We initiate the application of Statistical Thinking by identifying, documenting and defining the business process.  The Monthly-Billing-Process Example began by flowcharting and defining the billing process.   The team in the Customer-Complaint Process recognized that the process included raw material suppliers, the OEM manufacturer, and their customers.   Statistical Thinking recognizes that reducing variation is the key to success.  Often reducing variation involves recognizing the different types of variation.   The team in the Customer-Complaint-Process Example recognized the difference between special-cause and common-cause variation.

Usually Statistical Thinking requires the collection and analysis of data to estimate and reduce variation.  Statistical Thinking is data-driven decision making.   However, we need to define the overall process including its customer before collecting and analyzing data.   Also, the process definition includes available subject matter knowledge.   In the Monthly-Billing-Process Example, the process definition created knowledge concerning the process that did not exist without the flowcharts.   In the Customer-Complaint-Process example, the team recognized that it had to collect usage rates in order to estimate variation and identify special-cause outcome.  This process definition allows us to collect the appropriate data and focus our analysis.

Britz, Emerling, et al (2000, p26) point out two key advantages of Statistical Thinking and data-driven decision making.

1. Managers react to the last outcome.   If it is satisfactory, everyone is pleased and satisfied that the system is performing well.   If it is unsatisfactory, the implication is that something needs correction.   Results from common-causes are treated as resulting from special causes.  The analysis to reduce common-cause variation is much more effective if results from multiple outcomes are used.  Trying to find a special cause when one does not exist leads to frustration.
2. The lack of data makes everyone an expert.   Individual opinions vary and conflict with each other.

The figure depicts the relationship among Statistical Thinking, data and statistical methods.   Effective application of statistical methods occurs after performing Statistical Thinking.   In the Customer Complaint Process Example, a control chart and designed experiments occur after Statistical Thinking.   Lynne Hare points out in the reference by Britz, Emerling, et al (2000, p27) that he was successful in getting increased use of statistical tools only after explaining Statistical Thinking to managers.   They would not permit employees to use tools when they did not understand their purpose.

1. Britz, G. C., D. W. Emerling, et al. (2000). Improving Performance Through Statistical Thinking. Milwaukee, WI, ASQ Quality Press.