Statistical Tools for Experimental Design: Process and Product Development

This section is about SPC, a collection of tools that are essential in quality‐improvement activities. Statistical methods play a vital role in quality improvement. Some applications are outlined next:

1. In product and/or process design development, statistical methods, including designed experiments, can be used to compare different materials, components, or ingredients and to help determine both system and component tolerances. This application can significantly lower development costs and reduce development time.
2. Statistical method can be used to determine the capability of a manufacturing process. SPC can be used to systematically improve a process by reducing variability.
3. Experimental design methods can be used to investigate improvements in the process. These improvements can lead to higher yields and lower manufacturing costs.
4. Life testing provides reliability and other performance data about the product. This can lead to new and improved designs and products that have longer useful lives and lower operating and maintenance costs.

It is essential that engineers, scientists, managers, and policy makers have an in‐depth understanding of these statistical tools in any industry or business that wants to be a high‐quality, low‐cost producer. In this section we provide an introduction to the basic methods of statistical quality control that, along with experimental design, form the basis of a successful quality‐improvement effort.

SPC has its origins in the 1920s. Dr. Walter A. Shewhart of the Bell Telephone Laboratories was one of the early pioneers of the field. In 1924 he wrote a memorandum illustrating a control chart, one of the basic SPC tools. World War II saw the widespread dissemination of these methods to US industry. Dr. Edward Deming and Dr. Joseph Juan were instrumental in spreading the methodology after World War II.

SPC is a set of problem‐solving tools that may be applied to any process. The following are the major tools of SPC:

1. Stem‐and‐leaf diagram
2. Histogram
3. Pareto chart
4. Cause‐and‐effect diagram
5. Defect‐concentration diagram
6. Control chart
7. Scatter diagram
8. Check sheet

Although these tools are an important part of SPC, they comprise only the technical aspect of the subject. An equally important element of SPC is attitude – a desire of all individuals in the organization for continuous improvement in quality and productivity through the systematic reduction of variability. The control chart is the most powerful of the SPC tools. For complete discussion of these methods, see Montgomery (2009).