Designation:E2281−15AnAmericanNationalStandardStandardPracticeforProcessCapabilityandPerformanceMeasurement1ThisstandardisissuedunderthefixeddesignationE2281;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thispracticeprovidesguidancefordeterminingprocesscapabilityandperformanceunderseveralcommonscenariosofuseincluding:(a)normaldistributionbasedcapabilityandperformanceindicessuchasCp,Cpk,Pp,andPpk;(b)processcapabilityusingattributedatafornon-conformingunitsandnon-conformitiesperunittypevariables,and(c)additionalmethodsinworkingwithprocesscapabilityorperformance.2.ReferencedDocuments2.1ASTMStandards:2E456TerminologyRelatingtoQualityandStatisticsE2334PracticeforSettinganUpperConfidenceBoundForaFractionorNumberofNon-Conformingitems,oraRateofOccurrenceforNon-conformities,UsingAttributeData,WhenThereisaZeroResponseintheSample2.2OtherDocument:MNL7ManualonPresentationofDataandControlChartAnalysis33.Terminology3.1Definitions—Unlessotherwisenoted,allstatisticaltermsaredefinedinTerminologyE456.3.1.1longtermstandarddeviation,σLT,n—samplestandarddeviationofallindividual(observed)valuestakenoveralongperiodoftime.3.1.1.1Discussion—Alongperiodoftimemaybedefinedasshifts,weeks,ormonths,etc.3.1.2processcapability,PC,n—statisticalestimateoftheoutcomeofacharacteristicfromaprocessthathasbeendemonstratedtobeinastateofstatisticalcontrol.3.1.3processcapabilityindex,Cp,n—anindexdescribingprocesscapabilityinrelationtospecifiedtolerance.3.1.4processperformance,PP,n—statisticalmeasureoftheoutcomeofacharacteristicfromaprocessthatmaynothavebeendemonstratedtobeinastateofstatisticalcontrol.3.1.5processperformanceindex,Pp,n—indexdescribingprocessperformanceinrelationtospecifiedtolerance.3.1.6shorttermstandarddeviation,σST,n—theinherentvariationpresentwhenaprocessisopera...
