Statistical Thinking to Improve Quality

The previous blog post describes an application of Statistical Thinking to increase customer satisfaction by examining the processes starting with the raw material supplier and ending with the customer use of the product.   This example illustrates important features of Statistical Thinking described by Britz, Emerling et al (2000).   These features include:

1. Reducing variation improves performance.   The team had training in Statistical Thinking so they understood the various types of variation.   One type is common-cause variation which is always present.   Another type is special-cause variation which is due to isolated events.   One way to reduce overall variation is to identify outcomes that have a significant special-cause variation component.  For those outcomes, we can analyze the circumstances causing the increased variation.    To reduce common-cause variation, we need to analyze the all outcomes not affected by special causes.   The team knew this so they collected data to help them identify outcomes due to special causes.    A control chart which is a statistical method is a common approach for identifying outcomes affected by special causes.
2. The team had management support.   An understanding of Statistical Thinking facilitates management support.   Management had to support the tactic of going to the customer and convincing them to collect usage data so the team could estimate defect rates.   The team explained the concepts of Statistical Thinking to the customer to gain their support.   Note that management and the customer did not have to have a detailed understanding of the statistical methods.  When the team discovered that the importance of raw material, they had to convince management to support designed experiments to reduce common-cause variation.   My experience is that management can be very reluctant to approve designed experiments unless they appreciate the principles of Statistical Thinking.
3. Reducing variation is often a sequential process.   The team went after special-cause variation and then discovered a potential contributor to common-cause variation.

References

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