Quantifiable Process Capability Analysis Task
A Quantifiable Process Capability Analysis Task is a statistical analysis task for a quantifiable process.
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- Counter-Example(s):
- See: Industrial Process, Process Analysis, Process Error Rate.
References
2012
- http://www.pqsystems.com/qualityadvisor/DataAnalysisTools/capability_analysis.php
- QUOTE: Capability analysis is a set of calculations used to assess whether a system is statistically able to meet a set of specifications or requirements. To complete the calculations, a set of data is required, usually generated by a control chart; however, data can be collected specifically for this purpose.
Specifications or requirements are the numerical values within which the system is expected to operate, that is, the minimum and maximum acceptable values. Occasionally there is only one limit, a maximum or minimum. Customers, engineers, or managers usually set specifications. Specifications are numerical requirements, goals, aims, or standards. It is important to remember that specifications are not the same as control limits. Control limits come from control charts and are based on the data. Specifications are the numerical requirements of the system.
All methods of capability analysis require that the data is statistically stable, with no special causes of variation present. To assess whether the data is statistically stable, a control chart should be completed. If special causes exist, data from the system will be changing. If capability analysis is performed, it will show approximately what happened in the past, but cannot be used to predict capability in the future. It will provide only a snapshot of the process at best. If, however, a system is stable, capability analysis shows not only the ability of the system in the past, but also, if the system remains stable, predicts the future performance of the system.
Capability analysis is summarized in indices; these indices show a system’s ability to meet its numerical requirements. They can be monitored and reported over time to show how a system is changing. Various capability indices are presented in this section; however, the main indices used are Cp and Cpk. The indices are easy to interpret; for example, a Cpk of more than one indicates that the system is producing within the specifications or requirements. If the Cpk is less than one, the system is producing data outside the specifications or requirements. This section contains detailed explanations of various capability indices and their interpretation.
- QUOTE: Capability analysis is a set of calculations used to assess whether a system is statistically able to meet a set of specifications or requirements. To complete the calculations, a set of data is required, usually generated by a control chart; however, data can be collected specifically for this purpose.
2008
- (Upton & Cook, 2008) ⇒ Graham Upton, and Ian Cook. (2008). “A Dictionary of Statistics, 2nd edition revised." Oxford University Press. ISBN:0199541450
- QUOTE: Capability Analysis: Method determining the extent to which the long-term performance of an industrial process complies with engineering requirements or managerial goals. Often it is required that output should lie between upper and lower specification limits (USL; LSL). One measure of the extent to which this is achieved is the potential capability, [math]\displaystyle{ C_p, }[/math], given by [math]\displaystyle{ C_p = \frac{USL - LSL}{6\sigma} }[/math] where [math]\displaystyle{ \sigma }[/math] is the standard deviation of the output distribution. An equivalent statistic is [math]\displaystyle{ C_r }[/math] the capability ratio, which is [math]\displaystyle{ 1/C_r }[/math].