ASTM E2281-08

This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately,ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
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Designation:E2281–03 Designation: E 2281 – 08
Standard Practice for
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Process and Measurement Capability Indices
This standard is issued under the fixed designation E2281; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
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e NOTE—Section 3 was corrected editorially in May 2007.
1. Scope
1.1 Thispracticeprovidesguidancefortheuseofcapabilityindicesforevaluatingprocesscapabilityandperformance.Process
capabilityindicescomparethevariabilityofaprocessqualitymeasureagainstproductspecificationsortolerancesandassumethe
process is in a state of statistical control. Process performance indices are useful in situations when the process is not in a state
of statistical control.
2. Referenced Documents
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2.1 ASTM Standards:
E456 Terminology Relating to Quality and Statistics
2.2 ISO Standard:
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ISO 3534-2 Statistics—Vocabulary and Symbols-Statistical Quality Control
2.3 Other Document:
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MNL 7 Manual on Presentation of Data and Control Chart Analysis
3. Terminology
3.1 DefinitionsDefinitions: Unless—Unless otherwise noted, all statistical terms are defined in Terminology E 456.
3.1.1
3.2 Definitions of Terms Specific to This Standard:
3.2.1 average standard deviation, s¯, n—arithmetic average of sample standard deviations.
3.1.2
3.2.2 long term standard deviation, s , n—sample standard deviation of all individual (observed) values taken over a long
LT
period of time.
3.1.2.1
3.2.2.1 Discussion—A long period of time may be defined as shifts, weeks, or months, etc.
3.1.3
3.2.3 lower process capability index, C , n—index describing process capability in relation to the lower specification limit.
pkl
3.1.4
3.2.4 lower process performance index, P , n—index describing process performance in relation to the lower specification
pkl
limit.
3.1.5
3.2.5 minimum process capability index, C , n—smalleroftheupperprocesscapabilityindexandthelowerprocesscapability
pk
index.
3.1.6
3.2.6 minimum process performance index, P , n—smaller of the upper process performance index and the lower process
pk
performance index.
3.1.7
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This practice is under the jurisdiction of ASTM Committee E11 on Quality and Statistics and is the direct responsibility of Subcommittee E11.30 on Data Analysis.
Current edition approved June 10, 2003. Published July 2003.
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This practice is under the jurisdiction ofASTM Committee E11 on Quality and Statistics and is the direct responsibility of Subcommittee E11.30 on Statistical Quality
Control.
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Current edition approved April 1, 2008. Published June 2008. Originally approved in 2003. Last previous edition approved in 2003 as E2281–03 .
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ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
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Available from American National Standards Institute, 11 W. 42nd St., 13th Floor, New York, NY 10036.
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Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E2281–08
3.2.7 process capability, PC, n—statisticalestimateoftheoutcomeofacharacteristicfromaprocessthathasbeendemonstrated
to be in a state of statistical control.
3.1.8
3.2.8 process capability index, C , n—an index describing process capability in relation to specified tolerance.
p
3.1.9
3.2.9 process performance, PP, n—statisticalmeasureoftheoutcomeofacharacteristicfromaprocessthatmaynothavebeen
demonstrated to be in a state of statistical control.
3.1.10
3.2.10 process performance index, P , n—index describing process performance in relation to specified tolerance.
p
3.1.11
3.2.11 range, R, n—the largest observation minus the smallest observation in a set of values or observations.
3.1.12
3.2.12 short term standard deviation, s , n—the inherent variation present when a process is operating in a state of statistical
ST
control, expressed in terms of standard deviation.
3.1.12.1
3.2.12.1 Discussion—This may also be stated as the inherent process variation.
3.1.13
3.2.13 special cause, n—source of intermittent variation in a process. ISO3534-2
3.1.13.1 ISO 3534-2
3.2.13.1 Discussion—Sometimes “special cause” is taken to be sy
...