Editing Statistical process control (section)

== History ==
Statistical process control was pioneered by [[Walter A. Shewhart]] at [[Bell Laboratories]] in the early 1920s. Shewhart developed the control chart in 1924 and the concept of a state of statistical control. Statistical control is equivalent to the concept of [[exchangeability]]<ref>{{harvnb|Barlow|Irony|1992}}</ref><ref>{{harvnb|Bergman|2009}}</ref> developed by logician [[William Ernest Johnson]] also in 1924 in his book ''Logic, Part III: The Logical Foundations of Science''.<ref>{{harvnb|Zabell|1992}}</ref> Along with a team at AT&T that included [[Harold F. Dodge|Harold Dodge]] and Harry Romig he worked to put [[Sampling (statistics)|sampling]] inspection on a rational statistical basis as well. Shewhart consulted with Colonel Leslie E. Simon in the application of control charts to munitions manufacture at the Army's [[Picatinny Arsenal]] in 1934. That successful application helped convince Army Ordnance to engage AT&T's [[George D. Edwards]] to consult on the use of statistical quality control among its divisions and contractors at the outbreak of World War II.

[[W. Edwards Deming]] invited Shewhart to speak at the Graduate School of the U.S. Department of Agriculture and served as the editor of Shewhart's book ''Statistical Method from the Viewpoint of Quality Control'' (1939), which was the result of that lecture. Deming was an important architect of the quality control short courses that trained American industry in the new techniques during WWII. The graduates of these wartime courses formed a new professional society in 1945, the [[American Society for Quality Control]], which elected Edwards as its first president. Deming travelled to Japan during the Allied Occupation and met with the Union of Japanese Scientists and Engineers (JUSE) in an effort to introduce SPC methods to Japanese industry.<ref>{{cite book |author-link=W. Edwards Deming |first=W. Edwards |last=Deming |title=Lectures on statistical control of quality |publisher=Nippon Kagaku Gijutsu Remmei |edition=Rev. 2nd |date=1952 |oclc=2518026 }}</ref><ref>Deming, W. Edwards and Dowd S. John (translator) Lecture to Japanese Management, Deming Electronic Network Web Site, 1950 (from a Japanese transcript of a lecture by Deming to "80% of Japanese top management" given at the Hotel de Yama at Mr. Hakone in August 1950)</ref>

==='Common' and 'special' sources of variation===
{{Main|Common cause and special cause (statistics)}}
Shewhart read the new statistical theories coming out of Britain, especially the work of [[William Sealy Gosset]], [[Karl Pearson]], and [[Ronald Fisher]]. However, he understood that data from physical processes seldom produced a [[normal distribution]] curve (that is, a [[Gaussian distribution]] or '[[Normal distribution|bell curve]]'). He discovered that data from measurements of variation in manufacturing did not always behave the same way as data from measurements of natural phenomena (for example, [[Brownian motion]] of particles). Shewhart concluded that while every process displays variation, some processes display variation that is natural to the process ("''common''" sources of variation); these processes he described as being ''in (statistical) control''. Other processes additionally display variation that is not present in the causal system of the process at all times ("''special''" sources of variation), which Shewhart described as ''not in control''.<ref>{{cite book |title=Why SPC? |publisher=SPC Press |isbn=978-0-945320-17-3 |year=1992}}</ref>

===Application to non-manufacturing processes===

Statistical process control is appropriate to support any repetitive process, and has been implemented in many settings where for example [[ISO 9000]] quality management systems are used, including financial auditing and accounting, IT operations, health care processes, and clerical processes such as loan arrangement and administration, customer billing etc. Despite criticism of its use in design and development, it is well-placed to manage semi-automated data governance of high-volume data processing operations, for example in an enterprise data warehouse, or an enterprise data quality management system.<ref>{{cite book |first=Larry |last=English |title=Improving Data Warehouse and Business Information Quality: Methods for Reducing Costs and Increasing Profits |publisher=Wiley |date=1999 |isbn=978-0-471-25383-9 }}</ref>

In the 1988 [[Capability Maturity Model]] (CMM) the [[Software Engineering Institute]] suggested that SPC could be applied to software engineering processes. The Level 4 and Level 5 practices of the Capability Maturity Model Integration ([[CMMI]]) use this concept.

The application of SPC to non-repetitive, knowledge-intensive processes, such as research and development or systems engineering, has encountered skepticism and remains controversial.<ref>{{cite journal |first1=Bob |last1=Raczynski |author2-link=Dr Bill Curtis |first2=Bill |last2=Curtis |title=Point/Counterpoint: Counterpoint Argument: Software Data Violate SPC's Underlying Assumptions |journal=IEEE Software |volume=25 |issue=3 |pages=49–51 |date=May–June 2008 |doi=10.1109/MS.2008.68 }}</ref><ref>{{cite journal |first=Robert V. |last=Binder |title=Can a Manufacturing Quality Model Work for Software? |journal=IEEE Software |volume=14 |issue=5 |pages=101–5 |date=September–October 1997 |doi=10.1109/52.605937 |s2cid=40550515 }}</ref><ref>{{Cite web|last=Raczynski|first=Bob|date=February 20, 2009|title=Is Statistical Process Control Applicable to Software Development Processes?|url=https://www.stickyminds.com/article/statistical-process-control-applicable-software-development-processes|website=StickyMinds|language=en}}</ref>

In ''No Silver Bullet'', [[Fred Brooks]] points out that the complexity, conformance requirements, changeability, and invisibility of software<ref>{{Cite journal |author-link=Fred Brooks | last1 = Brooks, Jr. | first1 = F. P.| doi = 10.1109/MC.1987.1663532 | title = No Silver Bullet—Essence and Accidents of Software Engineering | journal = Computer | volume = 20 | issue = 4 | pages = 10–19 | year = 1987 | url = http://faculty.salisbury.edu/~xswang/Research/Papers/SERelated/no-silver-bullet.pdf| citeseerx = 10.1.1.117.315}}</ref><ref name="Brooks, Proc. IFIP" >{{cite conference |first=Fred P. |last=Brooks |title=No Silver Bullet&nbsp;— Essence and Accident in Software Engineering |book-title=Information processing 86: proceedings of the IFIP 10th World Computer Congress|publisher=North-Holland |date=1986 |isbn=978-0-444-70077-3 |pages=1069–76 }}</ref> results in inherent and essential variation that cannot be removed. This implies that SPC is less effective in the software development than in, e.g., manufacturing.