Statistical process control (SPC) procedures can help you monitor process behavior.
Arguably the most successful SPC tool is the control chart, originally developed by Walter Shewhart in the early 1920s. A control chart helps you record data and lets you see when an unusual event, e.g., a very high or low observation compared with “typical” process performance, occurs.
Control charts attempt to distinguish between two types of process variation:
Various tests can help determine when an out-of-control event has occurred. However, as more tests are employed, the probability of a false alarm also increases.
A marked increase in the use of control charts occurred during World War II in the United States to ensure the quality of munitions and other strategically important products. The use of SPC diminished somewhat after the war, though was subsequently taken up with great effect in Japan and continues to the present day. (For more, see The History of Quality)
Many SPC techniques have been “rediscovered” by American firms in recent years, especially as a component of quality improvement initiatives like Six Sigma. The widespread use of control charting procedures has been greatly assisted by statistical software packages and ever-more sophisticated data collection systems.
Over time, other process-monitoring tools have been developed, including:
More recently, others have advocated integrating SPC with Engineering Process Control (EPC) tools, which regularly change process inputs to improve performance.
Contributed by Keith M. Bower, a statistician and webmaster of www.KeithBower.com.