常规定性分析方法的不确定度之评估Word文档下载推荐.docx
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常规定性分析方法的不确定度之评估Word文档下载推荐.docx
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Copyright©
2003PublishedbyElsevierScienceB.V.
UncertaintyofresultsinroutinequalitativeanalysisA.Pulido,I.Ruisá
nchez,,R.Boqué
andF.X.Rius
DepartamentdeQuí
micaAnalí
ticaiQuí
micaOrgá
nica,UniversitatRoviraiVirgili,Pç
a,ImperialTà
rraco1,E-43005,Tarragona,Spain
Availableonline2December2003.
Abstract
Uncertaintyisaperformancecharacteristicthatshouldbeestimatedinbothquantitativeandqualitativeresultsinordertoimproveknowledgeoftheirreliability.Contrarytoquantitativeresults,uncertaintyinqualitativeanalysiscannotbeexpressedasanintervalaroundthepredictedvalue.Theuncertaintyisprobabilisticinnatureasitmightexpresstheprobabilityoftakingawrongdecision.Inthisarticle,wereviewfourdifferentwaysofestimatingtheuncertaintyofaqualitativeorscreeningsystem:
contingencytables;
Bayes’theorem;
statisticalintervals;
and,performancecurves.Wepayparticularattentiontotheiradvantagesanddrawbacks,andtheirmainapplications.
AuthorKeywords:
Cut-offvalues;
Performancecharacteristics;
Qualitativeanalysis;
Screeninganalysis;
Uncertainty
ArticleOutline
1.Introduction
2.Methodsforestimatinguncertaintyinqualitativeanalysis
2.1.Contingencytables
2.2.Bayes’method
2.3.Statisticalintervals
2.4.Performancecurves
3.Conclusions
Acknowledgements
References
1.Introduction
Screeninganalyticalmethodologiesareemerginginanalyticallaboratoriesbecauseoftheneedtoproducereliableinformationrapidly.Analyticalmethodsthatprovideimmediateresponsessothatimmediatedecisionscanbetakenareinconsiderabledemand.Decision-makingisthereforeakeypointwhendealingwithscreeningsystems,aswearemoreinterestedinstatingwhetherornotasamplecomplieswithlegislationthaningivinganaccurateconcentrationresult.Thegeneraltrendistodevelopanalyticalsystemsthatprovidebinaryresponsesoftheyes/notype,indicatingwhetherananalyteisaboveorbelowaspecifiedlimit,normallyimposedbylegislationorclients.Inadditiontothis,qualitativeorscreeningmethodshaveimportantadvantages,suchaslowercosts,rapidity,simplicityorminimizationoferrorsbecauseofdelaysbetweensamplingandanalysis,amongothers[1].
Asinanyotheranalyticalmethods,qualitativeandscreeningmethodsmustbevalidatedbeforebeingusedfortestingunknownsamples.Typicalperformancecharacteristics,suchasaccuracy,robustness,measurementuncertainty,andlimitofdetection,mustbeknowntoensurethatthemethodisfitforpurpose.Inthisarticle,wefocusononeoftheseperformancecharacteristics:
themeasurementofuncertainty.
Althoughbeinganoldtopicofresearch,ashasbeenrecentlydiscussed[2],uncertaintyinquantitativeanalysishasbeenextensivelystudied[3,4and5]sincepublicationoftheISOGuidetotheExpressionofUncertaintyinMeasurement(GUM)andtheEurachemtranslationtochemicalanalysisin1995[6].However,thereareveryfewstudiesonuncertaintyinqualitativeanalysis.Itshouldbepointedoutthatseveralpapershavementionedtheneedforstudiesofthissort[1,2,7and8].
Uncertaintyinqualitativeanalysiscannotbeexpressedinthesamewayasinquantitativeanalysis,thatistosay,asaparameterthatcharacterizesthedispersionoftheresults.Onthecontrary,thetypicalformofuncertaintyisprobabilisticinnature,anditmightbeexpressedastheprobabilityofmakingawrongdecision.Forexample,abloodanalysisindicatesthatapatienthasdiabeteswithX%probabilityofbeingwrong.Inanotherexampleontheimplementationofborder-crossingenvironmentalregulations,thesamplehasaY%probabilityofcomplyingwiththelegislation.Thebinaryresponseanddecision-makingyes/noarisefromaninstrumentalmeasurement,atestkit(involvingasensorialchange,suchasappearanceorchangeincolor)orothers.Likeallmeasurementprocesses,itinvolvessomeerrors,whichshouldberandomorattributabletothecorrectionofbias;
theseerrorsaretheoriginofanuncertaintyinthefinalresults.Theconceptofuncertaintyandtheprobabilitiesofcommittingfalsepositivesandfalsenegativeshavetobetakenintoaccountinordertomakeacompliancedecision.
Severalstudiesdiscusshowtorelateuncertaintytoqualitativeresults,buttherearenoindicationsofthebestapproachforagivenapplication[7].Inthisarticle,wereviewcurrentapproachesformeasuringtheuncertaintyofaresultinaqualitativeanalyticalmethod.Allofthemarebasedonprobabilitycalculations.Contingencytables[9],Bayes’Theorem[10]andperformancecurves[11]havebeendescribedandseveralapplicationsofthemcanbefoundintheli
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