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The circular safety region: a useful graphical tool in capability analysis
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
2005 (English)In: Quality and Reliability Engineering International, ISSN 0748-8017, E-ISSN 1099-1638, Vol. 21, no 5, p. 529-538Article in journal (Refereed) Published
Abstract [en]

When measuring the capability of a manufacturing process some form of process capability index is often used. To assess the capability, using a random sample, confidence intervals or hypothesis tests on the index are frequently used. Here, an alternative approach is presented. A process is usually defined to be capable if the capability index exceeds a stated threshold value, e.g. Cpm > 4/3. This inequality can be expressed graphically as a region in the plane defined by the process parameters (µ, σ). This graphical region, or safety region, similar to a confidence region for ((µ, σ). can be plotted to test for capability. Under the assumption of normality a circular safety region for the capability index Cpm is constructed that can be used to draw conclusions about the capability at a given significance level. This simple graphical approach is helpful when trying to understand if it is the variability, the deviation from target or both that need to be reduced to improve the capability. Using circular regions several characteristics can be monitored in the same plot.

Place, publisher, year, edition, pages
2005. Vol. 21, no 5, p. 529-538
National Category
Probability Theory and Statistics
Research subject
Mathematical Statistics with special emphasis on Industrial Statistic
Identifiers
URN: urn:nbn:se:ltu:diva-9793DOI: 10.1002/qre.739ISI: 000231043300010Scopus ID: 2-s2.0-23744466454Local ID: 87955500-9598-11db-8975-000ea68e967bOAI: oai:DiVA.org:ltu-9793DiVA, id: diva2:982731
Note
Validerad; 2005; Bibliografisk uppgift: Special Issue: Innovation in Business and Industrial Statistics . Issue Edited by Martina Vandebroek; 20061227 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved

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Vännman, Kerstin

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CiteExportLink to record
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  • apa
  • harvard1
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  • de-DE
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  • nn-NB
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  • Other locale
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Output format
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