Editing Control chart (section)

==History==
The control chart was invented by [[Walter A. Shewhart]]  working for [[Bell Labs]] in the 1920s.<ref>{{cite web|url=http://www.porticus.org/bell/westernelectric_history.html#Western+Electric+-+A+Brief+History|title=Western Electric History|website=www.porticus.org|access-date=2015-03-26|archive-url=https://web.archive.org/web/20110127163844/http://www.porticus.org/bell/westernelectric_history.html#Western+Electric+-+A+Brief+History|archive-date=2011-01-27|url-status=dead}}</ref> The company's engineers had been seeking to improve the reliability of their [[telephony]] transmission systems. Because [[amplifier]]s and other equipment had to be buried underground, there was a stronger business need to reduce the frequency of failures and repairs. By 1920, the engineers had already realized the importance of reducing variation in a manufacturing process. Moreover, they had realized 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's boss, George Edwards, recalled: "Dr. Shewhart prepared a little memorandum only about a page in length. About a third of that page was given over to a simple diagram which we would all recognize today as a schematic control chart. That diagram, and the short text which preceded and followed it set forth all of the essential principles and considerations which are involved in what we know today as process quality control."<ref>{{cite web|url=http://www.porticus.org/bell/doc/western_electric.doc|title=''Western Electric – A Brief History''|access-date=2008-03-14|archive-url=https://web.archive.org/web/20080511183038/http://www.porticus.org/bell/doc/western_electric.doc|archive-date=2008-05-11|url-status=dead}}</ref> 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.

Shewhart created the basis for the control chart and the concept of a state of statistical control by carefully designed experiments. While Shewhart drew from pure mathematical statistical theories, he understood that data from physical processes typically produce a "[[normal distribution]] curve" (a [[Gaussian distribution]], also commonly referred to as a "[[Normal distribution|bell curve]]"). He discovered that observed variation in manufacturing data did not always behave the same way as data in nature ([[Brownian motion]] of particles). Shewhart concluded that while every process displays variation, some processes display controlled variation that is natural to the process, while others display uncontrolled variation that is not present in the process causal system at all times.<ref>"Why SPC?" British Deming Association SPC Press, Inc. 1992</ref>

In 1924, or 1925, Shewhart's innovation came to the attention of [[W. Edwards Deming]], then working at the [[Hawthorne facility]]. Deming later worked at the [[United States Department of Agriculture]] and became the mathematical advisor to the [[United States Census Bureau]]. Over the next half a century, Deming became the foremost champion and proponent 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 for 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 1960s.

Bonnie Small worked in an Allentown plant in the 1950s after the [[transistor]] was made. Used Shewhart's methods to improve plant performance in quality control and made up to 5000 control charts. In 1958, ''The Western Electric Statistical Quality Control Handbook'' had appeared from her writings and led to use at AT&T.<ref name="Best & Neuhauser 2006">{{cite journal |last1=Best |first1=M |last2=Neuhauser |first2=D |title=Walter A Shewhart, 1924, and the Hawthorne factory |journal=Quality and Safety in Health Care |date=1 April 2006 |volume=15 |issue=2 |pages=142–143 |doi=10.1136/qshc.2006.018093 |pmid=16585117 |pmc=2464836 }}</ref>