Statistical process control: Difference between revisions

Revision as of 18:59, 6 December 2023

Revision as of 16:27, 21 February 2024

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==='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? |agency=British Deming Association |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.

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*{{cite journal |author-link=W. Edwards Deming |first=W. E. |last=Deming |title=On probability as a basis for action |journal=The American Statistician |volume=29 |issue=4 |pages=146–152 |date=1975 |doi=10.1080/00031305.1975.10477402 |pmid=1078437 |s2cid=21043630 }}

*{{cite book |author-mask=1 |first=W.E. |last=Deming |title=Out of the Crisis: Quality, Productivity and Competitive Position |date=1982 |isbn=0-521-30553-5 }}

*{{cite book |first=E.L. |last=Grant |title=Statistical quality control |publisher= McGraw-Hill|___location= |date=1946 |isbn={{Format ISBN|0071004475}} |pages= |url=https://catalog.hathitrust.org/Record/003053820?type%5B%5D=all&lookfor%5B%5D=Statistical%20quality%20control%201946&filter%5B%5D=authorStr%3AGrant%2C%20Eugene%20Lodewick%2C%20b.%201897&ft= }}

*{{cite book |first=J. |last=Oakland |title=Statistical Process Control |publisher= |___location= |date=2002 |isbn=0-7506-5766-9 }}

*{{cite book |first=T. |last=Salacinski |title=SPC — Statistical Process Control |publisher=The Warsaw University of Technology Publishing House |date=2015 |isbn=978-83-7814-319-2 }}