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The control chart was invented by Walter A. Shewhart while working for the Western Electric Company . The company's engineers had been seeking to improve the reliability of their telephony transmission systems. Because amplifiers and other equipment had to be buried underground, there was a business need to reduce the frequency of failures and repairs. By 1920 they had already realised the importance of reducing variation in a manufacturing process. Moreover, they had realised that continual process-adjustment in reaction to non-conformance actually increased variation and degraded quality. Shewhart framed the problem in terms of Common- and special-causes of variation and, on May 16 1924, wrote an internal memo introducing the control chart as a tool for distinguishing between the two. Shewhart stressed that bringing a production process into a state of statistical control , where there is only common-cause variation, and keeping it in control, is necessary to predict future output and to manage a process economically.
In 1938, Shewhart's innovation came to the attention of W. Edwards Deming, then working at the United States Department of Agriculture but about to become mathematical advisor to the United States Census Bureau. Over the next half a century, Deming became the foremost champion and exponent of Shewhart's work. After the defeat of Japan at the close of World War II, Deming served as statistical consultant to the Supreme Commander of the Allied Powers. His ensuing involvement in Japanese life, and long career as an industrial consultant there, spread Shewhart's thinking, and the use of the control chart, widely in Japanese manufacturing industry throughout the 1950s and 1960sCenturies: 19th century 20th century 21st century Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s 2010s Years: 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 Events and trends The 1960s was a turbulent decade of change around.
More recent use and development of control charts in the Shewhart-Deming tradition has been championed by Donald J. Wheeler . Control charts play a central role in the Six SigmaSix Sigma is a quality management program to achieve "six sigma" levels of quality. It was pioneered by Motorola in the mid- 1980s and has spread to many other manufacturing companies. It continues to spread to service companies as well. In 2000, Fort Way management strategy.
A control chart is a run chart of a sequence of quantitativeA quantitative property can be meaningfully measured using numbers; properties which aren't quantitative are called qualitative . Examples of quantitative properties include: the number of grains of sand on a beach, the width of a hair, and the time for a data with three horizontal lines drawn on the chart:
Common cause variation plots as an irregular pattern, mostly within the control limits. Any observations outside the limits, or patterns within, suggest (signal) a special-cause (see Rules below). The run chart provides a context in which to interpret signals and can be beneficially annotated with events in the business.
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