Chapter 7 Summary and Concluding Remarks

When World War II ended, U.S. manufacturing changed its emphasis from producing mainly defense equipment to producing products for civilian consumption. At this time, many of the quality control techniques that were used so effectively during the war years fell into relative disuse. It was competition from foreign companies that were using quality control techniques that motivated American companies to re-emphasize the use of these techniques. In addition, the use of these practices has spread from solely manufacturing to other areas such as administrative processes and health care delivery.

The use of computers, and results of recent research, can enable dramatic increases in the efficiency of Statistical Quality Control methods over what was possible in 1945. In Chapters 2 and 3, it has been shown that the use of the computer makes it quick and easy to develop OC curves and average sample size curves that are useful in comparing different acceptance sampling plans. Understanding how to develop and interpret these curves can greatly clarify the differences in various proposed sampling plans. In addition, programs have been written that allow quick access to published sampling schemes that are normally used in domestic and international trade.

The use of the computer greatly reduces the time involved to iteratively develop Shewhart control charts with Phase I data. Other simple computer displays of data, such as Pareto Diagrams and Scatter plots etc., greatly help in determining the assignable causes for out-of-control conditions that may appear on Phase I control charts. More sophisticated statistical tools such as PDCA and designed experiments can detect assignable causes that may not be obvious with observational data.

More recently developed time-weighted control chart such as the Cusum and EWMA charts can greatly reduce the expected time to detect out of control signals in Phase II monitoring of process data. In addition, they can reduce the chance of falsely concluding an assignable cause is present when there is none. This can greatly improve the operation of any process.

This book has emphasized the use of the public domain program R for SPC and Acceptance Sampling calculations. In addition to getting a CQPA Certification from the American Society for Quality (ASQ), students in this course who learn to use this tool, will be able to make immediate contributions in the job market where there is a strong demand for Quality Analysts and Quality Engineers.