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Weight of Evidence
Citation preview
WeightofEvidence:areviewofconceptandmethods
DouglasL.Weed
reviewedby:N.Basilico,D.LaniadoRiskAnalysis,Vol.25,No.6,2005
Introduction
animportantissueintheprocessofscientificdiscovery:experimentumcrucis(crucialexperiment)
itisadeterminativeexperimentthatcreatesnewscientificconsensus examplescanbefoundinphysics,chemistryandengineering
Introduction
publichealth:difficulttofindcrucialexperiments ingeneralasingleexperimentcannotresolveacriticalissueonthecauseofadisease
severalformsofevidenceindirectlyconnectedtothephenomenon
someformofaggregationisneededinordertoevaluateacausalhypothesis
Introduction
WOE:takingintoaccountdifferentkindsofscientificevidenceinassessingthevalidityofacausalhypothesis
itisthemethodcurrentlyusedbyregulatoryagenciesinriskassessmentprocess
ObjectiveandMethodology objective:findoutthemenaningoftheexpression"weightofevidence"inrecentliterature
computerizedPubMedlibrarysearch selectionof92papersinwhichtheterm"weightofevidence"(WOE)wasused allpublicationsfrom2003to2004(71) allpublicationsfrom1994to2002inwhich"WOE"appearedinthetitle(21)
UsesofWOE
threedifferentusesoftheexpressionWOEhavebeenidentified: methaphorical methodological(withseveralsubcategories) theoretical
MetaphoricalUse
mostcommonuse notreferredtoanyparticularmethod themethodissupposedtobeimplicitlyunderstandable
lackoftransparency
MethodologicalUse
strenghtofevidence useonlyasubsetoftheevidence(onlypositiveandstatisticallyrelevantoronlyunbiasedevidence)
weightofevidence takeintoaccountalltheevidence
MethodologicalUse
useofestabilishedinterpretativemethodologies systematicnarrativereviews qualitycriteriafortoxicologicstudies epidemiology'scausalcriteria metaanalisys mixedepidemiologytoxicologymethods
SystematicNarrativeReviews
describingthestateofscience makingresearchrecommendationstoauthorsabouthowtodoclaimsofcausality,orpreventiverecommendations
fosteringclarityandtrasparencyindescribinginterpretativemethods
QualityCriteriaforToxicologicStudies
classifyingtoxicologicalstudiesaccordingtotheirquality: reliablewithoutrestriction reliablewithrestriction notreliable notassignable
first2classes:includedintheintepretativeprocess last2classes:includedwithacasebycaseapproach
Epidemiology'sCausalCriteria
givenabodyofstatisticallysignificantepidemiologicalevidenceandsomelabbasedevidence howcanbeestabilishedifthereisacausalrelationship? Ourobservationsrevealanassociationbetweentwovariables[...]Whataspectsofthatassociationshouldweespeciallyconsiderbeforedecidingthatthemostlikelyinterpretationofitiscausation?(A.B.Hill,1965)
Epidemiology'sCausalCriteria
plausibility coherence experimentation analogy
strenght consistency specificity temporality biologicalgradient(doseresponse)
Hillidentified9differentcriteria:
MetaAnalysis
quantitativeapproachforsummarizingevidencefromseveralhumanpopulationstudies
contributionofeachstudyisweightedbytheinversevarianceoftheeffectestimate
notsufficienttostatecausalitybutitcanprovideareproducibleweightedaverageoftheestimateofeffectacrossseveralstudies
MixedEpidemiologyToxicologymethods
methodstocombineepidemiologicalevidenceandlabbasedbiologicalevidence
whatisbiologicalplausibility?1.amechanismcanbehypothesized
2.somelabbasedevidencesupportsthehypothesis
3.sufficientevidencetoshowhowthefactorinfluencesaknowndiseasemechanism
QuantitativeWeightingSchemes
identifyingasetofattributes examples:strenghtofassociation,temporalrepresentativeness,useofastandard
assigningaweighttoeachelementaccordingtotheoverallsatisfactionofattributes
WOEintheory
WOEapproachusedtounderstandhowvisualpatternsareperceivedasregularphenomena(figuralgoodness)
canexplainwhysymmetryisperceivedasmoreregularthanrepetition
incognitivescience(E.M.Pothos,R.Ward,2000)
WOEintheory
inlaw>aconceptualframeworkforaWOEapproachbasedon4features: relevance reliability sufficiency standardofproof
Problems&Proposals
lackoftransparency encourageauthorstodescribetheinterpretativemethodsused
multiplicityofWOEdefinitionsandapplications movingtowardstheuseoffamiliarandwellestabilishedcriteria
differentkindsofweights roleofjudgement
Critics
Lettertotheeditor(I.Linkov,2006) noncomprehensivesearchmethods lackofcriticalappraisalofincludedstudies missedstudies notastateofthesciencereview
Discussion
clearformalizationofthemethodologiescanhelptoreducethesubjectivityofjudgements
wemustbeawarethatnointerpretativemethodcanabstractfromexpertjudgement furtherinvestigationisneededinordertoclearlydefinetheroleofexpertjudgementinthedifferentusesofWOEmethodologies
References Weed,D.L.(2005).Weightofevidence:areviewofconceptandmethod.RiskAnalysis,25(6),
15451557.
Hill,A.B.(1965).Theenvironmentanddisease:Associationorcausation?JournaloftheRoyalSocietyofMedicine,58,29530
Pothos,E.M.,andWard,R.(2000).Simmetry,repetition,andfiguralgoodness:Aninvestigationoftheweightofevidencetheory.Cognition,75(3),B6578
Krimsky,S.(2005).Theweightofscientificevidenceinpolicyandlaw.AmericanJournalofPublicHealth,95(S1),S129S136
Linkov,I.(2006).WeightofEvidence:WhatistheStateoftheScience?RiskAnalysis,26(3),573575.
Weed,D.L.(1997).Ontheuseofcausalcriteria.InternationalJournalofEpidemiology,26,11371141.
Weed,D.L.,andHursting,S.D.(1998).Biologicplausibilityincausalinference:Currentmethodandpractice.AmericanJournalofEpidemiology,147,415425.