5Material Contribution to Injury

Illustrative Cases: Bonnington, Bailey, O2, Rahman, Fitzgerald

Factual Basis

This analysis is applied where:

• therearemultiplefactors(notallofwhichneedtobetortious);• thecaseisnotoneofoverdeterminationorpre-emption;• ithasbeenestablishedthatthetortiousfactor/shavehadanactualeffect1 on the

claimant’spositionattrial;andeither• theinjuryisdivisibleinprinciple,butitisnotpossibletoattributeconstituent

partstoparticularfactorsonthefactsofagivencase(Bonnington);or• theinjuryisindivisible(Bailey, O2, Rahman).

A‘materialcontributiontoinjury’analysisisappropriatewhereitismorelikelythannotthatatleastonedefendant’sbreachhasmadeadifferencetotheclaim-ant’soutcome,but it isnotpossible to isolate thephysicaleffectsof individualbreachesfromoneanother.Thisimpossibilityprecludestheapplicationofbasiccausalprinciples.Forinstance,inafactualscenarioliketheoneinPerformance Cars Ltd v Abraham,2thereweretwophysicallydistinctinstancesofdamagetotheclaimant’scar,eachofwhichcouldbelinkeddiscretelytoaparticulardefendant.3 Bycontrast,thosesituationsinwhichacourtshouldresorttoa‘materialcontribu-tiontoinjury’analysisarethosewherethefact4ofadefendant’scontributionto

1 Thequestionofwhatthisamountstoisacontentiousoneandwillbeexaminedindetailbelow.Insummary,undertheNBA,afactormusthavebeenanecessaryoneintheclaimant’sinjuryoccurringasandwhen itdid inorder toamount toamaterialcontribution.Thisdoesnotaccordwith the idea,expressedinSienkiewicz v Greif[2011]UKSC10,[2011]2AC229at[90]265(perLordPhillips)andinBonnington Castings v Wardlaw [1956]AC613(HL)at621(perLordReid)thatsuchafactorneedonlyhavemadeacontributioninexcessofade minimislevelinordertobedeemedamaterialcontribution.

2 Performance Cars Ltd v Abraham[1956]1QB33(CA).3 Inthiscase,suchanexercisewasastraightforwardonebecausethedamagetotheclaimant’scar

occurredintwoconsecutivechronologicalstages,butthisisnotnecessaryforaninjurytobedivisible.Wereacartohavebeenhitbytwoothervehiclessimultaneously,itmightofcoursestillbepossibletolinkseparablepartsofthetotaldamagetoeachparticularcollision.

4 Inthesenseoftheclaimanthavingproven,onthebalanceofprobabilities,thatbutforthedefend-ant’sbreach,hernaturalcourseofeventswouldhavebeenunaffected.

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damagehasbeenestablished,but thereareother factors involved, and there issimplynomeansofdiscretelyassigningconstituentpartsofthatdamagetopar-ticularfactors.Inthecaseof indivisible injuries, this isbecausesuchdamageisbinaryinnatureandsocannotbebrokendownintoconstituentparts.Inthecaseof injuriesdivisible in theory, theproblemarisesbecause it isnotpossibleasamatterofevidencetoidentifyanycleancorrespondencebetweenconstituentpartsandmultiplepotentialfactors.

InjuryIsDivisibleinPrinciplebutItIsNotPossibletoAttributeConstituentPartstoParticularFactors

TheclassicexampleofthiscategoryofcaseisBonnington Castings v Wardlaw,5 in whichtheclaimantcontractedpneumoconiosisduringthecourseofhisemploy-mentbythedefendants.Thereweretwofactorsidentifiedascontributingtothisdisease:first,thoseparticlesofsilicadustintheworkplaceatmospherewhichhademanatedfromswinggrindersandsecond,thoseparticlesofsilicadustwhichhadcomefrompneumatichammers.Whilstbothtypesofworkplacemachinerywerethe legalresponsibilityofthedefendants,6 theyhadonlybreachedtheirdutyinrelationtothefirst,sincetherewasnoknownorpracticablemeansofreducingthedustescapingfromthelatter.Thismeantthattheparticularquestionforthecourtinthiscasewaswhetherthedustresultingfromthedefendant’sbreachcouldbecausallylinkedtotheclaimant’sinjury.TheessenceofthisproblemwasidentifiedbyLordKeith:

Thediseaseisadiseaseofgradualincidence.Smallthoughthecontributionofpollutionmaybeforwhichthedefendersaretoblame,itwascontinuousoveralongperiod.Incumulo,itmusthavebeensubstantial,thoughitmightremainsmallinproportion.Itwastheatmosphereinhaledbythepursuerthatcausedhisillnessanditisimpossible,inmyopinion,toresolvethecomponentsofthatatmosphereintoparticlescausedbythefaultofthedefendersandparticlesnotcausedbythefaultofthedefenders,asiftheywereseparateandindependentfactorsinhisillness.Primafacietheparticlesinhaledareactingcumulatively,andI think thenatural inference is thathad itnotbeen for thecumulativeeffectthepursuerwouldnothavedevelopedpneumoconiosiswhenhedidandmightnothavedevelopeditatall.7

ThespecificproblemposedforthecausalinquirybyBonningtonstemsfromthefactthateachpotentialcausalfactor(iethe‘innocent’dustandthe‘guilty’dust)

5 Bonnington Castings v Wardlaw[1956]AC613(HL).Although,asLordRodgerstatesinFairchild v Glenhaven Funeral Services[2002]UKHL22,[2003]1AC32at[129]100:‘Theideaofliabilitybasedon wrongful conduct that had materially contributed to an injury was . . . established long beforeWardlaw.ButWardlaw becameaconvenientpointofreference,especiallyincasesofindustrialdisease’.

6 Covered specifically by regulation 1 of the Grinding of Metals (Miscellaneous Industries)Regulations1925.

7 [1956]AC613(HL)at626(perLordKeith).

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wasoperatingontheclaimantconcurrently.8Asadirectresultofsuchconcur-rence,thecausalinquirycouldnotrelyontheincrementalnatureofthedisease’sdevelopment to attribute causal valence to particular factors in the way that itcouldifthefactorshadbeenoperatingconsecutively.

Bonningtonmayrepresentadeparturefromthe...orthodoxapproachinthecontextofaparticularevidentiarygap:namely,whereitisknownthatthevictim’stotalcondi-tionisadivisibleonebutthereisnoacceptableevidentiarybasisonwhichthedisabilityduetotheseparateinsultstothebodycouldbeapportionedtotheindividualsources,theclaimantisallowedtorecoverforthetotalcondition...thepursuercouldproveanorthodoxcausalconnectionbetweenbreachandapartofthedivisibleinjury,hejustcouldnotquantifyit.9

An ‘acceptable evidentiary basis’ of the type lacking in Bonnington would existwheretherelevantpotentialcausalfactorsaffectedtheclaimantduringseparateconsecutiveperiods,meaning thateachcouldbe linked toaparticular stageofdevelopment,andthereforedivisiblepart,oftheinjury.Suchisthefactualbasisofcases inwhichorthodoxapportionmentcanbecarriedout.Take, forexample,Thompson v Smiths Shiprepairers (North Shields) Ltd,10inwhichMustillJ(ashethen was) reasoned as follows about the situation which would representBonnington weretheinnocentandguiltydustfactorstohaveoperatedconsecu-tively,asopposedtoconcurrently:

Next,onemustconsiderhowthisapproachcanbeappliedtoacasewhereeither(a)therearetwosuccessiveemployers,ofwhomonlythesecondisatfault,or(b)thereisasingleemployer,whohasbeenguiltyofanactionablefaultonlyfromadateaftertheemploymentbegan . . .EmployerBhas . . . ‘inherited’aworkmanwhosehearing isalreadydamagedbyeventswithwhichthatemployerhashadnoconnection,oratleastnoconnectionwhichmakeshimliableinlaw.Thefactthat,sofarastheworkeriscon-cerned,theprioreventsunfortunatelygivehimnocauseofactionagainstanyoneshouldnotaffect theprinciplesonwhichhe recovers fromemployerB. Justice looks to theinterestsofbothparties,nottothoseoftheplaintiffalone.11

ThisdistinctionbetweentheconcurrentnatureofthefactorsinBonnington and theconsecutiveoperationofthefactorsinThompsonexplainswhy,althoughbothinjuriesaredivisibleinprinciple,onlythedamageinthelattercasewasdivisibleinpractice.Therefore,Bonningtonrequiresamaterialcontributiontoinjuryanal-ysis, whereas Thompsondoesnot.Lookedatinthisway,thematerialcontributionanalysisappears tobe relatively simple.Thereare,however, twocomplicationsthathaveariseninrelationtoit.Thefirstisaquestionmarkoverwhateffecttheimpositionofliabilityformaterialcontributiontoinjuryshouldhaveonaconse-

8 ‘[C]oncurrent in effect, if not necessarily in time’ – Thompson v Smiths Shiprepairers (North Shields) Ltd [1984]QB405(QB)at442(MustillJ).

9 JStapleton,‘UnnecessaryCauses’(2013)129LQR39,52–53.SeealsoJStapleton,‘Lordsa’LeapingEvidentiaryGaps’(2002)10Torts Law Journal276,283onwards.

10 [1984]QB405(QB).SeeCh3,textton24.11 [1984]QB405(QB)at438.

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quentawardofdamages,and the second iswhetheramaterialcontribution toinjuryanalysisisanapplicationof,oranexceptionto,theButFortest.Thefirstquestionnodoubtarisesbecause,aswesee fromBonnington, injuries whicharedivisibleinprinciplewillsometimescallforliabilitytobeassessedonamaterialcontributiontoinjurybasiswherethatdivisibilityisnotpossibleinprac-tice, but where there have been multiple potential causal factors. Facts such asthosearisinginBonnington thereforeoccupysomethingofahalfwayhouse.Itistritenegligencelawthat,wherepossible,defendantsshouldonlybeheldliableforthatpartoftheclaimant’sultimatedamagetowhichtheycanbecausallylinked,asisclearfromcasessuchasThompson and Performance Cars.Itisequallytritethat,whereadefendanthasbeenfoundtohavecausedorcontributedtoanindi-visibleinjury,shewillbeheldfullyliableforit,eventhoughtheremaywellhavebeenothercontributingcauses:12

[I]tis...hard–andsettledlaw–thatadefendantisheldliableinsolidumeventhoughallthatcanbeshownisthathemadeamaterial,say5%,contributiontotheclaimant’sindivisibleinjury.Thatisaformofroughjusticewhichthelawhasnothithertosoughttosmooth,preferringinstead,asamatterofpolicy,toplacetheriskoftheinsolvencyofawrongdoerorhisinsurerontheotherwrongdoersandtheirinsurers.13

SincetheinjuryinBonningtonistheoreticallydivisible,itseemsnottofitintothissecondcategory,butitcannomorefitintothefirstbecausethereis,aswehaveseen,nopracticalbasisonwhichanysensibledivisioncouldbemade.14 This was notaquestionwhichtroubledtheCourtinBonnington,sincethedefendants’casewas that they were not liable for the damage at all; they made no plea for anyapportionmenttobemadeonthebasisthattheirbreachofdutywasnottheonlycausalfactorinvolvedintriggeringpneumoconiosis.Theveryfact,however,thatnoapportionmentwasmade,hasledtoquestionsbeingaskedsubsequentlyastowhetherthatconclusionwasthepurelytheresultoftheconductofthatparticularcase,orwhetherthesameoutcomewouldhaveoccurredforsubstantivereasons,hadthedefendantsrequestedthatitbeconsidered.15

Theansweristhatthereshouldbenoapportionmentincaseswhichrequire,onthebasisoutlinedinthischapter,amaterialcontributiontoinjuryanalysis.Theargumentthatapportionmentofdamagesisnotappropriateincasesinwhichadefendanthasmateriallycontributed toan indivisible injury is both well estab-lishedandeasytojustify.16Thereis,however,noobviousordefensiblereasonwhyadifferentapproachshouldbetakenwhereapracticalsegmentationisnomorefeasible,despitethefactthatthedamageinquestionmightbetheoretically divisible

12 See,eg,Dingle v Associated Newspapers[1961]2QB162(CA)at188(perDevlinLJ),Hotson v East Berkshire Health Authority[1987]AC750(HL)at783(perLordHarwich)andJSmith,‘Causation–theSearchforPrinciple’[2009]Journal of Personal Injury Law101,103.SeealsoBaldwin & Sons Pty Ltd v Plane (1998) 17 NSWCCR 434 (NSWCA), Bendix Mintex Pty Ltd v Barnes (1997) 42 NSWLR 307(NSWCA)andGates v Howard Rotavator Pty Ltd (2000)20NSWCCR7(NSWCA).

13 Barker v Corus[2006]UKHL20,[2006]2AC572at[90]607–08(perLordRodger).14 Stapleton,‘Lordsa’Leaping’,aboven9at283.15 See,forexample,Stapleton,‘UnnecessaryCauses’,aboven9at52.16 Seenn12and13above.

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innature.17Asillustratedabove,hadthefactorsinBonningtonoperatedconsecu-tively, the damage therein would have been both theoretically and practicallydivisible.Thisisbecausethecumulativenatureofpneumoconiosis(whichiswhatmakesitdivisibleintheory)wouldhavelentitselftobeingdividedupchrono-logicallyaccordingtotheextentofitsdevelopmentduringtheperiodofexposuretoeachsuccessivefactor.AmaterialcontributiontoinjuryapproachwouldnotthereforehavebeennecessarybecausesuchfactswouldhavebeenamenabletoconventionalcausalanalysisalongthesamelinesasThompson.18Theveryfactthatsuchdivisionwasnotpossibleiswhatmakesitanappropriatecaseforanalysisonthebasisofmaterialcontributiontoinjury.Oncethispracticalimpossibilityexists,thereisnoeffectivemeansofdistinguishingbetweendivisibleandindivisibleinju-ries,sinceacourtisnomoreablesensiblytodivideuptheonethantheother.Adefendantwhohasbeenfoundtohavemateriallycontributedtosuchaninjury,therefore,shouldbeheldliablefor100percentoftheclaimant’sdamages.19

The answer to the second question, of whether the material contribution toinjuryanalysis isanapplicationof,oranexceptionto, theButFortest,canbemadeequallyemphatically:itadheresto,anddoesnotdepartfrom,thebasisofButForcausation.Aswillbecomeclear,thefirststageoftheNBA,whichisbasedonaggregateButForcausation,hasstilltobesatisfiedwhereamaterialcontribu-tiontoinjuryanalysisisapplied,justasitdoesinothertypesofcase.

1 – Is it more likely than not that a defendant’s breach of duty changed the claimant’s normal course of events so that damage (including constituent parts of larger damage) occurred which would not otherwise have done when it did?

Underthisanalysis,adefendant’sbreachhaseithertohavepart-caused an indivis-ible injury, or caused part ofa(theoretically)divisibleinjury.Unless,however,adefendanthasmadeadifference to theclaimant’scourseofevents in thisway,therewillbenoliability.20

Injury Is Indivisible

Anindivisibleinjuryisonewhichcannotbebrokendownintoseparableconstitu-entparts.Itisobvious,giventhischaracteristic,whyaquantificationofrespective

17 But see Sienkiewicz v Greif[2011]UKSC10,[2011]2AC229at[90]265(perLordPhillips).And,inorderforamaterialcontributiontoinjuryanalysistobeappropriate,theinjurymustbydefinitionbeonewhichcannotpracticallybedividedupamongstdiscretecausalfactors.

18 [1984]QB405(QB)at438.19 AccordingtoJaneStapleton,thisistheapproachadoptedbytheUScourtsinasbestosisclaims–

seeJStapleton,‘TheTwoExplosiveProof-of-CausationDoctrinesCentraltoAsbestosClaims’(2009)74 Brooklyn Law Review1011.Thisisalsosubject,asoutlinedbelow(seetextton38)toapossiblereductionincertainheadsofdamageifthecourtdecidesthattheinjurymighthaveoccurredatsomepointinthefutureowingtofactorsunrelatedtothedefendant’sbreachofduty.

20 Thisargumentwillbeaddressedfullybelow,wherethecaseofBailey v Ministry of Defence [2008] EWCACiv883,[2009]1WLR1052isdiscussed.

Factual Basis 99

contributionscannotbecarriedoutamongstmultiplefactors.21Someofthemoreobviousexamplesofindivisibleinjuryincludealimbbrokeninoneplaceatatime,psychiatric injury22anddeath.Psychiatric injurywas thedamage forwhichtheclaimantsoughtrecoveryinacasewhichhascometoberegardedasoneofthemostdifficultinthisarea:Rahman v Arearose Ltd.23AnNBA,however,clarifies themainissues.

In Rahman,theclaimantwasworkingforthefirstdefendantsasthemanagerofafastfoodrestaurantwhenhewasattackedbytwoblackyouths.Theinjurieshesustainedduringthatattacknecessitatedhishavingabonegraftinhiseyeattheseconddefendant’shospital.Thefirstdefendantsbreachedtheirdutybynotpro-viding sufficient protection for their employee, whilst the second defendant’sbreachlayinthenegligentperformanceoftheoperationonhiseye.Ultimately,therewereseveraldimensionstotheclaimant’sdamage.First,hewasblindintheeyeonwhichtheoperationhadbeenperformed.Inaddition,hedevelopedpost-traumatic stress disorder, a severe depressive disorder of psychotic intensity, aspecific phobia of Afro-Caribbean people with paranoid elaboration, and anenduringpersonalitychange;allofwhichlefthimunabletowork,oreventofunc-tionnormallyinsociety.Itwasthispsychiatricaspectofhisdamagewhichwasforensicallycontentious.AsaresultoftheCourtofAppeal’sconsiderationofthecase,

theclaimantgotjudgmentagainsteachdefendantforpartofhislossonly.Forhispainandsuffering/lossofamenityheobtainedjudgmentfor£7.5kagainsttheemployerand£55kagainstthehospital,andforhiseconomiclossofabout£500k,onequarteragainsttheemployerandthree-quartersagainstthehospital...24

LawsLJ’sjudgment,withrespect,makesthecausationissuesinthecaseappeartobefarmorecomplexthaninfacttheyare.AnapplicationoftheNBAleadstothesimple conclusion that both defendants should have been jointly and severallyliableforthewholeofthedamagefollowingthenegligentoperation.25Thefirst

21 Thisisthecorrectwaytoanalysethewell-knownUScaseofYbarra v Spangard154P2d687(Cal1945),inwhichthedefendantsufferedatraumaticarminjurywhilstundersedationforanunrelatedsurgicalprocedure.Theallegeddifficultyinhiscasewasthathecouldnotidentifyexactlyhoworbywhichmemberoftheteamintheatrehisinjurywascaused.Applyingres ipsa loquitur, however, the SupremeCourtofCaliforniadecidedinfavouroftheclaimant,andheld,interalia,thathedidnothavetoprovewhichpartywasresponsibleforthephysicaltraumabecause,inanyevent,eachpractitionerhadbreachedadutytoensurehissafetywhilstintheatre.Thisiscorrect,andpreciselytheresultthatwouldbereachedonanNBA:sinceallmembersofthesurgicalteamhadbreachedaduty,therewasat leastaggregateButForcausationand,sincehissafetywascompromisedintheatre,everybreachofthatdutywasoperativeonhimatthetimehisinjuryoccurred.Onthisview,itisastraightforwardcaseofmaterialcontributiontoanindivisibleinjury.

22 AsaresultofRahman v Arearose Ltd[2001]QB351(CA),somedoubthasbeencastonthisclas-sification.Astheanalysisbelowwillmakeclear,however,psychiatricinjuryisindeedindivisible.

23 [2001]QB351(CA).24 TWeir,‘TheMaddeningEffectofConsecutiveTorts’(2001)60CLJ237,238.25 Asconcededbycounselforthefirstdefendants,andacknowledgedat[2001]QB351(CA)at[36]

(perLawsLJ),adistinctionmustbemadebetweenthepre-operationandpost-operationlosses:sincethe effect of the second defendant’s breach could clearly not be operative on the claimant until itoccurred,thequestionofmultiplefactorssimplydoesnotarisepriortothesecondbreachoccurring.

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stageoftheNBAisclearlysatisfied,sinceitismorelikelythannotthatatleastonedefendant’sbreachofdutychangedtheclaimant’snormalcourseofeventsfortheworse.Thesecondstage,askedofthetwodefendantsinturn,wouldalsobesatis-fiedineachcase,sincetheeffectsofbothwerestilloperativeontheclaimantwhenhesufferedthedamageforwhichheclaimed.ContrarytotheviewofLawsLJ,theclaimant’s psychiatric injury should properly have been classed as indivisibleharm,sincehisongoingsufferingcouldnotbedisaggregatedandassignedtosep-aratecauses.WhilstLawsLJgavedetailedconsiderationtothequestionofwhetherthepsychiatricinjuryresultingfromthetwodefendants’breachescouldbesaidtobe ‘thesamedamage’forthepurposesoftheCivilLiability(Contribution)Act1978,heultimatelyheldthatitwasnot.HisLordship’sdecisionappearedtogivemuchweightto

anabsurdreportconfectedjointlybytheexpertsforthethreeparties,whotentativelydividedupthevictim’spresentconditionintermsofthetwocauses.Theyshouldnothavebeenaskedtodothis,andtheiranswershouldhavebeenignored,forthereisnoscientificbasisforanysuchattributionofcausality:theclaimantisnothalf-madbecauseofwhatthefirstdefendantdidandhalf-madbecauseofwhattheseconddefendantdid,heisasmadasheisbecauseofwhatbothofthemdid.Hismaniaisaetiologicallyindis-cerptible...26

Theconclusionthenreachedwasthat

ontheevidence therespective tortscommittedby thedefendantswere thecausesofdistinctaspectsoftheclaimant’soverallpsychiatriccondition,anditispositivelyestab-lishedthatneithercausedthewholeofit...onecannot...drawarough-and-readyconclusiontotheeffectthatthisisreallyanindivisibleinjuryandtherefore‘samedam-age’withinsection1(1)ofthe1978Act.27

Withrespect,itisdifficulttoseehowtheclaimant’sultimatepsychiatricdamagecouldbedividedinto‘distinctaspects’,andWeir’sanalysisisthemorecoherent.WhilstRahmandidindeedsufferfrommorethanonemanifestationofmentaltrauma,inthathehadPTSD,depressionandphobia,itwouldbeneitherauthen-ticnorfeasibletoregardtheseashavingbeentheseparateanddiscreteresultsofindividualbreachesofduty.Notonlyisitfarmorelikelythatthetwodefendants’actionsworkedsynergisticallytobringabouttheclaimant’songoinginjury,butthetenorofmorerecentcaselawappearstosupporttheviewthatsuchdamageisindivisible.28Forinstance,HaleLJinHatton v Sutherland 29referstoRahman as a

Onbasic causationprinciples(seeCh3),thefirstdefendantisliableforalloftheclaimant’sdamageupuntilthetimethenegligentoperationwasperformed.ApplyingtheNBAconfirmsthissince,underitssecondstageofanalysingthepre-operationdamage(lossofearningsandremovalexpenses),thesec-onddefendant’sbreachwouldbefound(obviously)tobenotyetoperativeontheclaimant.SeealsoWright v Cambridge Medical Group[2011]EWCACiv669,[2013]QB312at[52]328and[129]347.

26 Weir,‘TheMaddeningEffect’,aboven24at238.27 [2001]QB351(CA)at[23]–[24]364–365.28 Althoughsomeheadsofdamage, suchas thefirst threeyears’ lossofearningsandreasonable

removalexpenses,wereattributedsolelytothedefendantemployersincetheypre-datedtheeffectsofthenegligentmedicaltreatment.Thisisstandardpracticeand,assuch,isunremarkable.

29 Hatton v Sutherland[2002]EWCACiv76,[2002]2AllER1at[37]–[40]17–18.

Factual Basis 101

case involving indivisible injury,30asdoesSmithLJ inDickins v O2 Plc.31 In an extra-judicialcontext, this latterview isreiterated innouncertain terms,whenpsychiatricdamageisdescribedas ‘par excellenceanindivisible injury’.32 In one sense,LawsLJconcedesthisinanindirectwaywhenhesaysofthecontentiousreportoftheexperts:

Itistruethatthisagreedevidencedoesnotpurporttodistributecausativeresponsibilityforthevariousaspectsoftheclaimant’spsychopathologybetweenthedefendantswithanysuchdegreeofprecisionaswouldallowforanexactquantificationbythetrialcourt;nodoubtanyattempttodosowouldbehighlyartificial.Butthelackofitcannotdrivethecaseintotheregimeofthe1978Acttowhich,inprinciple,itdoesnotbelong...Thefact-findingcourt’sdutyistoarriveatajustconclusionontheevidenceastotherespec-tivedamagecausedbyeachdefendant,evenifitcanonlydoitonabroad-brushbasiswhichthenhastobetranslatedintopercentages.33

Inessence,whathisLordshippreparestodohereistoapportionliabilitybetweendefendantsonabasisapparentlyunconnectedtothefactualmatrixofthecase.Such apportionment (one-quarter to the employers and three-quarters to thehealthauthority)wasinsteadcarriedoutaccordingtoanapparentlyimpression-isticaccountof therelativeculpabilityof thedefendants.Despite thestrikinglyheterodoxnatureofthisapproach,itwasvalidatedbyobiterremarksmadebyHaleLJintheCourtofAppealinHatton34 and,althoughtheHouseofLordsexpresslydeclinedtoofferaviewonthispointwhentheyconsideredthesamecase,35 the suggestionwasimplementedinDickins v O2 Plc.36

TheclaimantinDickins wassuingherformeremployerforpsychiatricinjurycausedbyexcessivestressatwork.Theevidencesuggestedthatshehadbeenpro-motedtoapositionbeyondhernaturalcapabilitiesandthatthishad,overtime,ledtohersufferingfrommentalhealthproblems,variouslycharacterisedasanxi-etyanddepression.OncetheCourtofAppealacceptedthatherworkproblemsstemmedfromabreachofduty,itwasfacedwithapotentialproblemofcausationinthat,besidesthesituationatwork,theclaimanthadavulnerablepersonality,andhadsufferedfrommentalhealthissuesinthepast.Inadditiontothis,shesuf-feredfromIBS,wasatthematerialtimeexperiencingdifficultiesinherrelation-shipwithherpartner(althoughtheevidencewasinconclusiveastowhetherthesephenomenawerecausesoreffectsofherstress),andhadalso,duringtherelevantperiod, had to move out of her home for nine months as a result of flooding. Thereexisted,therefore,severalnon-breachfactorswhichcouldpotentiallyhave

30 [2002]EWCACiv76,[2002]2AllER1at[37]17andagainat[40]18.31 Dickins v O2 Plc[2008]EWCACiv1144,[2009]IRLR58at[45]64.SeealsoWeir,‘TheMaddening

Effect’,aboven24at239,wherehesaysofRahman that‘theharmwasnotincremental,buttheindivis-ibleresultofasynergisticorcatalyticconcatenationofevents’.

32 Smith,‘Causation’,aboven12at103.33 [2001]QB351(CA)at[23]364.34 [2002]EWCACiv76,[2002]2AllER1.35 [2004]UKHL13,[2004]2AllER385at[63]405(perLordWalker).36 [2008]EWCACiv1144,[2009]IRLR58.

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contributed to the illness to which she eventually succumbed. In the Court ofAppeal,SmithLJsummarisedthetrialjudge’smeansofdealingwiththispoint:

FollowingtheguidancegiveninHatton,thejudgetookthoseothermattersintoaccountwhenapportioningthedamagesasto50%beingduetothetortand50%duetothenon-tortious factors.Before the judge,bothpartieshadaccepted that itwas right toapportionthedamages.Thedisputebetweenthemwasonlyastohowtheyshouldbeapportioned.37

Asaresultofthenatureofthedisputebetweentheparties,andthereforeofthegroundsofappeal,theCourtofAppealinDickinswasunableconclusivelytorec-tifythetrialjudge’smistake,whichlayinhisapportionmentofliabilityinrespectofanindivisibleinjurytowhichthedefendantmadeamaterialcontribution.Asin Hatton and Rahman,thiswasapparentlydoneona‘broadbrush’basis,accord-ingtointuitiveestimationsofrelativeculpability,andwasasinappropriateinthiscaseasitwasinthejudgmentsfromwhichittookitslead.Fortunately,thosewhoheard the Dickinsappealseemedmindedtodowhattheycouldtoarrestthedevel-opmentofthisnovelandill-advisedpractice.Forinstance,althoughtheircom-mentscouldonlybeobiter,therewascommendableforceintheremarksoftwooftheirLordshipsontheapportionmentpoint.SmithLJstated:

I respectfully wish (obiter) to express my doubts as to the correctness of Hale LJ’sapproachtoapportionment.Myprovisionalview(givenwithoutthebenefitofargu-ment)isthat,inacasewhichhastobedecidedonthebasisthatthetorthasmadeamaterialcontributionbutitisnotscientificallypossibletosayhowmuchthatcontribu-tion is(apart fromtheassessment that itwasmorethandeminimis)andwhere theinjurytowhichthathasledisindivisible,itwillbeinappropriatesimplytoapportiondamagesacrosstheboard.Itmaywellbeappropriatetobearinmindthattheclaimantwaspsychiatricallyvulnerableandmighthavesufferedabreakdownatsomepointinthefutureevenwithoutthetort.Theremaythenbeareductioninsomeheadsofdamageforfuturerisksofnon-tortiousloss.Butmyprovisionalviewisthatthereshouldnotbeanyrulethatthejudgeshouldapportionthedamagesacrosstheboardmerelybecauseonenon-tortiouscausehasbeeninplay.38

Inconcurringwiththatjudgment,SedleyLJadded:

Iamtroubledbythesharedassumptionabouttheappropriatenessofapportionmentonwhichthecasehasproceeded.Whilethelawdoesnotexpecttortfeasorstopayfordam-agethattheyhavenotcaused,itregardsthemashavingcauseddamagetowhichtheyhavemateriallycontributed.Suchdamagemaybelimitedinitsarithmeticalpurchasewhereonecanquantifythepossibilitythatitwouldhaveoccurredsoonerorlaterinanyevent;butthatisquitedifferentfromapportioningthedamageitselfbetweentortiousandnon-tortiouscauses.Thelattermaybecomeadmissiblewheretheaetiologyoftheinjurymakesittrulydivisible,butthatisnotthecase.39

37 [2008]EWCACiv1144,[2009]IRLR58at[39]63.38 [2008]EWCACiv1144,[2009]IRLR58at[46]64.39 [2008]EWCACiv1144,[2009]IRLR58at[53]65.

Factual Basis 103

Furthermore,TonyWeirpointsout that this isnot ‘justamatterofaesthetics.Consequencesensue.If,inthepresentcase,eitherdefendanthadbeeninsolvent,theclaimantwouldnothavebeenfullyindemnified’.40AsbothSmithandSedleyLJJmakeclear,41fullindemnityinsuchacaseasthismaywelltaketheformofreduceddamages,toaccountforthepossibilityofthesameinjuryoccurringinthefutureasaresultofnon-tortiouscauses.Thisistheorthodoxlegalapproach,andisfarsuperiortoonewhichemploysapportionmentcarriedouton‘thebasisofspeculationorguesswork’:42

Itisimportantconceptuallytodifferentiateapportionmentordivisibilityfromanotherperfectlycommonprocessintheassessmentofloss,whichistotakeaccountofthevicis-situdesoflifeorcontingenciesasapplicabletotheindividualclaimant.If,forexample,aclaimantsufferedfromanaturaldiseasefromwhichhewaslikelytodieinfiveyears,thecourtwouldtakethatfactintoaccountwhenlimitingdamagestoaperiodoffiveyears...Intruth,...[this]isnotapportionmentatall–whatthecourtisdoingistak-ing a snapshot of the claimant, at a point immediately prior to the accident, whichincorporatesatthattimealltheparticularnegativeorpositivefactorsintheclaimant’sownpastorfuture,aswellasthefuturefactorswhichmightafflictpersonsgenerally.Thecourt,whentakingintoaccountthecontingenciesandvicissitudesoflife,makesitsawardinanattempttoreproducethesnapshot,theobjectbeingtorestoretheclaimant,wartsandall,tothepositionhewasinbeforethetortwascommitted.43

To understand exactly why this is so, it is necessary to consider the temporaldimension of the causal inquiry. When we ask whether the claimant’s damagewouldhaveoccurredbutforadefendant’sbreach,thiscanonlymeaningfullybeunderstoodasmeaning‘Butforadefendant’sbreach,wouldtheclaimant’sdam-agehaveoccurredwhen it did?’44Unless it isunderstoodinthisway,aButForinquiryiseitherimpossibletoanswer,orlegallymeaningless,orboth.Consider,asanexample,aclaiminwhichdeathformsthegistofthedamage.Clearly,here,butforthedefendant’sbreach,theclaimantwoulddefinitelyhavedied.Atsomestage.45Thepointoflegalrelevanceisofcoursewhethertheclaimantwouldhavediedwhenshedidbut for thedefendant’sbreach.46Wheredeath isconcerned,

40 Weir,‘TheMaddeningEffect’,aboven24at238.41 AndSmithLJreiteratesextra-judiciallyinSmith,‘Causation’,aboven12at103.42 ThecorrectapproachwastakeninFitzgerald v Lane[1989]AC328(HL),inwhichtwodefendants,

actingindependently,werefoundtohavebeenequallyresponsiblefortheultimateindivisibleinjury(partialtetraplegia),alongsideasubstantialcontributionfromtheclaimanthimself.Afterreducingthetotaldamagesby50%forcontributorynegligence,thedefendantswereheldjointlyandseverallyliablefortheremaining50%.

43 LCaun,‘MultipleCausesofInjury’[2003]Journal of Personal Injury Law 96,107–08.44 Asalreadyapparentlyrecognisedinacademicliterature,butrarelytranslatedintoexpresspracti-

cal applications – see R Wright, ‘The NESS Account: Response to Criticisms’ in R Goldberg (ed),Perspectives on Causation(Oxford,HartPublishing,2011)n48andJStapleton,‘ChoosingWhatWeMeanby“Causation”intheLaw’(2003)73Missouri Law Review433,452–53.

45 See D Lewis, ‘Causation as Influence’ in J Collins, N Hall and LA Paul (eds), Causation and Counterfactuals (Cambridge,MA,TheMITPress,2004)86.Thesignificanceofthispointbecomesevenmoreacuteincasesinvolvingepidemiologicalevidence;seebelow,textton50.

46 AlthoughitissometimesobviousthatthisisreallywhattheButForinquiryisasking,thisisbynomeansuniversallythecase(norisituniversallyacceptedasbeingappropriate).

104 Material Contribution to Injury

therefore,anon-temporallyspecificButForinquirywillalwaysbeeasytoanswer,butitwilltellusnothingofvaluetothecausalinquiry.47 Where, on the other hand, thegistoftheclaimisdamageofsomeothertype,suchasabrokenleg,itwillbeimpossibletopredictwhetheraclaimantwouldeverhavesufferedsuchaninjuryatanypointintheirlife,wereitnotforthedefendant’sbreach.Aninquirysuchasthis one is therefore both impossible to conduct and lacks any legal purchase.Facileexamplesthesemaybe,buttheyillustrateclearlyhowimportantitisthatanyButForinquiryisimbuedwithtemporalspecificity.Withoutthis,aswehaveseen,nosuch testwillbeable todistinguishbetweenoverdeterminedandpre-emptedcausalinquiries.48Itisdifficulttodiscernareason,therefore,foromittingthiscrucialqualificationfromtheexpressformulationofthetest.49

Inaddition to thisconceptualargument, therearepractical justifications forwhy the causal inquiry should have as its focus the stage at which a claimantincurredthedamageofwhichsheultimatelycomplains.First,thespecificques-tion of whether an individual would have incurred damage when she did is an establishedpartofepidemiologicalcausaltheory:

Onedefinitionofthecauseofaspecificdiseaseoccurrenceisanantecedentevent,con-dition or characteristic that was necessary for the occurrence of the disease at themomentitoccurred,giventhatotherconditionsarefixed.Inotherwords,acauseofadisease occurrence is an event, condition or characteristic that preceded the diseaseonsetandthat,hadtheevent,conditionorcharacteristicbeendifferentinaspecifiedway,thediseaseeitherwouldnothaveoccurredatallorwouldnothaveoccurreduntilsomelatertime.50

It is easy to identify several significant reasons why claimants should want toremainundamagedforaslongaspossible.Clearly,mostofuswouldwanttodielaterratherthansooner,andthisappliesnotonlytoouremotionalandphysiolog-icalperspectives,butalsotothematerialeffectthatalongerlifewilloftenhaveonour estate. Where illness is concerned, similar arguments apply, in that peoplegenerallywillwanttohaveasmuchoftheir lifeaspossibleunaffectedbypain,sufferingandinfirmity.Inthecontextofpropertydamage,particularlywherethatpropertyisfungibleandreplaceable,thesignificanceoftimingisnotnecessarilysostriking fromthesubjectiveviewpointof theclaimant.Nevertheless, it remainslegallypertinentbecause,aswithpersonalinjury,determiningthepointatwhichadefendant’sbreachaffectedtheclaimantallowsacourteithertodividedamageupamongstseveralfactors(wherethisispossible)or,inanyevent,todetermine

47 Seetextton124below.48 Wright,‘TheNESSAccount’,aboven44atn125.49 WhichiswhatRichardWrighthaslongarguedforinrelationtotheUS Restatement:American

LawInstitute,82nd Annual Meeting, Proceedings 2005 (Philadelphia,PA,AmericanLawInstitute,2006)81–84(thusfarinvain–seeAmericanLawInstitute,Restatement of the Law, Third, Torts: Liability for Physical and Emotional Harm (StPaul,MN,AmericanLawInstitute,2010)§26).

50 K Rothman, S Greenland, T Lash, Modern Epidemiology 3rd edn (Philadelphia, PA, WoltersKluwer,2008)6.Thestatisticalimplicationsofthisforthelegaltestareexploredfurtherbelow.

Factual Basis 105

exactlywhataclaimanthaslostasaresultofherinjury.51ThefirststageoftheNBAexplicitlyincludesthistemporalconditionbyasking‘butforatleastonebreachofduty,wouldtheclaimant’sdamagehaveoccurredwhen it did?’

Thistimingissueistheprincipaldifferencebetweenmaterialcontributiontoinjurycasesandpre-emptedcausesituations.Aswehaveseen,52thelattertypeofsituationischaracterisedbythenon-duplicativeeffectsofthefactorsconcerned,sincepre-emptedfactorsarethosewhichneverhaveaneffectontheclaimant.Adefiningfeatureofmaterialcontributiontoinjurycases,ontheotherhand,isthemultipleeffectofdifferentfactorsontheclaimant,andthereisnorequirementforallofthefactorsconcernedtobebreachesofduty.So,evenifaclaimantisactuallyaffectedbybothbreachfactorsandnon-breachfactors,andevenifnon-breachfactorswouldeventuallyhaveledtothesamedamageoccurringatanypointinthefuture,53adefendantwillremainliableifherbreachhastenedtheoccurrence.Thequantificationofwhatsuchafactorhascausedaclaimanttoloseisasubsequent, and non-causal, question of damages.54 In the well-known US case of Dillon v Twin State Gas & Electric Co,55forexample,thedefendantwasheldliableforneg-ligentlyallowinga14-year-oldboytobeelectrocutedbyitselectriccables.Thefactthat,hadthedeceasednotgrabbedacable,hewouldhavefallentohisdeathoratleasttoseriousinjury,madenodifferencetothecausalquestion.Itwasrelevantonlytotheconceptuallydistinctissueofhowmuchthedefendanthadtopayinordertoredressitswrong.56

Consequently, in Dickins,57where theclaimanthadbeenaffectedbystressatwork,herownvulnerablepersonality,IBS,relationshipissuesanddomesticflood-ing, and where her depressive illness was ongoing, as it was at trial, the betteranalysisofthecasewouldhavebeenthatsuggestedintheobiterremarksofSmithandSedleyLJJ.58Thedefendantemployer’sbreachledtoMsDickins’breakdownhappeningwhenitdid,buttheotherfactorsaffectingherconcurrentlymadeitlikelythatshewouldhavesufferedthesamedamageatsomepointinthefutureanyway, meaning that the defendant employer’s liability could be described as hastening damage to which she was anyway vulnerable.59 It would, in such

51 Ifitwerepossibletodeterminethatabreachofdutyacceleratedtheoccurrenceofdamagethatwouldhaveoccurredatsometimeinthefutureinanyevent,thequantificationoftheclaimant’sdam-agesshouldreflectthis–seeMGreen,‘TheIntersectionofFactualCausationandDamages’(2006)55DePaul Law Review671,677–80.

52 SeeCh4.53 Evenamomentlater.54 SeeGreen,‘TheIntersection’,aboven51.55 Dillon v Twin State Gas & Electric Co163A111(NH1932).56 SeealsoRStevens,Torts and Rights(Oxford,OUP,2007) 134.57 [2008]EWCACiv1144,[2009]IRLR58.58 Seeabove,textton39.59 [2008]EWCACiv1144,[2009]IRLR58at[46]64.SeealsoJKingJr,‘Causation,Valuationand

ChanceinPersonalInjuryTortsInvolvingPre-ExistingConditionsandFutureConsequences’(1981)90 Yale Law Journal1353.

106 Material Contribution to Injury

circumstances,beopentoacourttoreducethedamagespayableaccordingly.60 Thishasbeenreferredtoasthe‘crumblingskulldoctrine’:

Theso-called‘crumblingskullrule’simplyrecognizesthatthepre-existingconditionwasinherentintheplaintiff’s‘originalposition’.Thedefendantneednotputtheplaintiffina position better thanhisorheroriginalposition.Thedefendantisliablefortheinjuriescaused,eveniftheyareextreme,butneednotcompensatetheplaintiffforanydebilitat-ingeffectsofthepre-existingconditionwhichtheplaintiffwouldhaveexperiencedany-way.Thedefendantisliablefortheadditionaldamagebutnotthepre-existingdamage ...ifthereisameasurableriskthatthepre-existingconditionwouldhavedetrimentallyaffectedtheplaintiffinthefuture,regardlessofthedefendant’snegligence,thenthiscanbetakenintoaccountinreducingtheoverallaward...Thisisconsistentwiththegeneralrulethataplaintiffmustbereturnedtothepositionhewouldhavebeenin,withallofitsattendantrisksandshortcomings,andnotabetterposition.61

Inthecasefromwhichthisexcerptistaken,Athey v Leonati,62 theSupremeCourtofCanadadealtmeticulouslywiththeparticularitiesofthematerialcontributiontoinjurymeansofanalysis.Inthatcase,theclaimant,whohadahistoryofbackproblems,hadbeeninjuredintwosuccessivecaraccidents,eachresultingfromthe defendants’ breach of duty.63 Subsequently, whilst performing a routinestretch,hesufferedadischerniationforwhichherequiredsurgery.Asaresult,hewasforcedtotakelower-paidemploymentsothathecouldavoidheavymanualwork.Thetrialjudgeawardedtheclaimant25percentoftheglobaldamagesfig-ureonthebasisthatthetwoaccidentswerenotthesolecauseoftheherniation,(becauseofthepre-existingbackproblems)butthattheyplayedacausativerole,estimatedtobeintheregionof25percent.TheCourtofAppealagreedwiththisassessment,buttheSupremeCourtrectifiedthismistakeconclusivelyandcon-structivelyinawardingfulldamagesagainstthedefendants.Itdidsoprimarilyonthebasis that the trial judgehadconcluded that ‘theplaintiffhasproven,onabalanceofprobabilities,thattheinjuriessufferedinthetwoearlieraccidentscon-tributedtosomedegreetothesubsequentdischerniation’.64MajorJ,ingivingthejudgmentoftheCourt,wentontosay:

Hadthetrialjudgeconcluded(whichshedidnot)thattherewassomerealisticchancethatthedischerniationwouldhaveoccurredatsomepointinthefuturewithouttheaccident,thenareductionoftheoveralldamageawardmayhavebeenconsidered.Thisisbecause theplaintiff is tobe returned tohis ‘originalposition’,whichmighthaveincludedariskofspontaneousdischerniationinthefuture.However,intheabsenceofsuchafinding,itremains‘speculative’andneednotbetakenintoconsideration.65

60 [2008]EWCACiv1144,[2009]IRLR58at[47]64.SeealsoADugdaleandMJones,Clerk & Lindsell on Torts,20thedn(London,Sweet&Maxwell,2010)2-161.

61 Athey v Leonati [1996]3SCR458(SCC)at[35].62 Athey v Leonati[1996]3SCR458(SCC).63 Althoughthereweretwodefendantsinfact,bothwererepresentedasoneatthetrial.64 [1996]3SCR458(SCC)at[44].65 [[1996]3SCR458(SCC)at[48].SeealsoGraham v Rourke(1990)75OR(2d)622(OntCA),

Malec v JC Hutton Proprietary Ltd[1990]HCA20,(1990)169CLR638andSchrump v Koot(1977)18OR(2d)337(OntCA).

Factual Basis 107

Evenmorehelpfully,theSupremeCourtexplicitlysummarisedtheprinciplesonwhichitreacheditsdecision:

Iftheinjuriessustainedinthemotorvehicleaccidentscausedorcontributedtothedischerniation,thenthedefendantsarefullyliableforthedamagesflowingfromtheher-niation.Theplaintiffmustprovecausationbymeetingthe ‘but for’ or material contribu-tion test.66Futureorhypotheticaleventscanbefactoredintothecalculationofdamagesaccordingtodegreesofprobability,butcausationoftheinjurymustbedeterminedtobeprovenornotproven.Thishasthefollowingramifications:

1. Ifthedischerniationwouldlikelyhaveoccurredatthesametime,withouttheinjuriessustainedintheaccident,thencausationisnotproven.2. Ifitwasnecessarytohaveboththeaccidentsandthepre-existingbackconditionfortheherniationtooccur,thencausationisproven,sincetheherniationwouldnothaveoccurredbutfortheaccidents.Eveniftheaccidentsplayedaminorrole,thedefendantwouldbefullyliablebecausetheaccidentswerestillanecessarycontribut-ingcause.3. Iftheaccidentsalonecouldhavebeenasufficientcause,andthepre-existingbackconditionalonecouldhavebeenasufficientcause,thenitisunclearwhichwasthecause-in-factofthedischerniation.Thetrialjudgemustdetermine,onthebal-anceofprobabilities,whetherthedefendant’snegligencemateriallycontributedtotheinjury.67

Thislastparagraphisslightlyambiguous.If itmeansthat,becausethejudgeinsuchasituationisunabletomakesuchadeterminationonthebalanceofproba-bilities therecanbeno liability, it iscorrect.Otherwise, it isdifficult to follow.Nonetheless, theAthey judgmentasawhole is tobewelcomedfor itsgenerallyconcise(atonly53shortparagraphs),straightforwardandaccurateexpositionofhowtoanalyseasituationinwhichtherehavebeenmaterialcontributionstoaninjury.

Attheotherendofthespectrum,ajudgmentapttocausemuchconfusionisthatoftheEnglishCourtofAppealinBailey v Ministry of Defence.68Theclaimantin this case suffered from severe brain damage, resulting from a cardiac arrestbroughtonbyheraspiratingherownvomit.Shehadattendedahospitalmanagedby the defendants in order that she might undergo a procedure, known as anERCP,toexamineandtreatasuspectedgallstoneinherbileduct.Itwasinrela-tiontotheclaimant’spost-operativecarethatthedefendantbreacheditsdutyofcare,sincetherewasafailuretoresuscitatetheclaimantduringthenightfollowingtheprocedure,leadingtoherbeingveryunwellbythefollowingmorning.Atthesame time, and unrelated to the defendant’s breach of duty, the claimant alsodevelopedpancreatitis,anillnesswhichisknowntooccurinsomepatientsfollow-ing an ERCP. More than a fortnight after her initial operation, the claimant

66 Emphasisadded–theseitalicshighlightanunfortunateflawintheCourt’sotherwisecoherentreasoning:asshouldnowbeapparent,theButForandmaterialcontributiontoinjuryanalysesarenotmutuallyexclusive.Rather,thelatterisaspecialisedapplicationoftheformer.

67 [1996]3SCR458(SCC)at[41].68 Bailey v Ministry of Defence[2008]EWCACiv883,[2009]1WLR1052.

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aspiratedhervomit,leadingtohercardiacarrestand,ultimately,tohypoxicbraindamage.For thepurposesof theappeal, thepertinent issuewas simply thatofwhether or not the defendant’s breach of duty in failing to give proper post- operativecare,wascausativeof theclaimant’sbraindamage.

Thereisnodoubt,accordingtothecriteriaoutlinedabove,thatthefactsofthiscaserequireamaterialcontributiontoinjuryanalysis.Forastart,thereweremul-tiplefactorsintheformofthedefendant’snegligentaftercareandthenaturallyoccurringpancreatitis.Furthermore,thiswasnotacaseofoverdeterminationorpre-emption.69Thepotentialcausalfactors inBailey couldonlybedescribedasinterdependentbecauseitisnotpossibletoestablishwhateffectsnegligentafter-care and pancreatitis would have if suffered separately. Their effects are bestdescribed as synergistic, or at least potentially so, meaning that Bailey belongsoutsideoftheduplicativecausecategory.Sincebraindamageisindivisibleinprin-ciple,itwasthereforenecessarytoestablishwhetherthedefendant’sbreachofdutyhadbeenapartialcauseoftheultimateinjury.Unfortunately,althoughthefactsofBaileywerecorrectlydeemedtorequireamaterialcontributiontoinjuryanaly-sis,thisisnotwhatfollowed.Whilst,withrespect,thereismuchtolamentinthejudgmentasawhole,70theessenceofthemistakeisencapsulatedinthefollowingstatementbyWallerLJ:

Inacasewheremedicalsciencecannotestablishtheprobabilitythat‘butfor’anactofnegligencetheinjurywouldnothavehappenedbutcanestablishthatthecontributionofthenegligentcausewasmorethannegligible,the‘butfor’testismodified,andtheclaimantwillsucceed.71

Thisproposition,whichformedthebasisoftheCourtofAppeal’sdismissalofthedefendant’sappealagainstliability,isdangerouslymisleading.AsStapletonpointsout,

until thatflawedproposition isdisapproved it threatens tohaveanexplosive impact inthefieldofmedicalnegligence.Thisisbecause,forexample,itmayoftenbethecasethatabreachbyamedicalproviderincreasestheweaknessofapatient,bysomenon-negligiblebutun-assessabledegree,beforethepatientsuffersanindivisibleinjurythatwouldhavebeenavoidedhadthepatientbeenofadequatestrength...Clearly,ifsuchclaimantsareentitledtosucceedunderthatpropositionitwouldexposemedicalpro-viderstoaradicallyexpandedrealmofliability.72

Thisexplainswhy,inordertobedeemedalegallyrelevantcause,afactormusteitherbeanecessarypart-causeof an indivisible injury,or thenecessary cause

69 SinceitdoesnotfitthecriteriaoutlinedinCh4.70 Suchasequatingmaterialcontributiontoinjurywiththeexceptionalmaterialcontributionto

riskanalysisdevelopedinFairchild v Glenhaven Funeral Services[2002]UKHL22,[2003]1AC32andadescriptionofthatcaseasoneinwhichtheevidenceestablishedthatonefibrecausedtheclaimant’sinjury.Foramoredetailedcriticismofthesearguments,seeCh6.

71 [2008]EWCACiv883,[2009]1WLR1052at[46]1069.72 Stapleton,‘UnnecessaryCauses’,aboven9at58.SeealsoMStauch,‘“MaterialContribution”asa

ResponsetoCausalUncertainty:TimeForaRethink’(2009)68CLJ 27,28–29.

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ofpartofa(theoretically)divisibleinjury.ThefirststageoftheNBAmust be satis-fiedinorderfortheretobeliabilityonthegroundsofamaterialcontributiontoinjury.

1 – Is it more likely than not that a defendant’s breach of duty changed the claimant’s normal course of events so that damage (including constituent parts of larger damage) occurred which would not otherwise have happened when it did?

Inhisproposition,WallerLJappearstoconflateButForwithde minimis non curat lex,byseeingthemasmutuallyexclusive,oratleastasalternatives.Sincebotharenecessary,thismaywellbethesourceofhisconfusion.Whereindivisibleinjury,suchasthatsufferedinBailey,isconcerned,aclaimantmustestablish,onthebal-anceofprobabilities,thatthedefendant’sbreachwasapart-causeofthatdamage.Inotherwords,shemustprovethat,butforthedefendant’sbreach,her injurywouldnothaveoccurredwhenitdid.Itmaywellbethecasethat,evenwhereaclaimanthasestablishedthatadefendant’sbreachwas,inButForterms,apart-causeofherinjury,acourtmaydecidethatthatcontributionwassosmallastoabsolvethedefendantfromliabilityonthebasisofthede minimisprinciple,butthe two principles are complementary and not alternative. The facts in Bailey shouldhave ledtoaconclusionofnoliabilitybecausetheexpertsthereinwereunable to say that, on the balance of probabilities, but for the negligent care, MsBaileywouldhaveavoidedhavingthecardiacarrest(whichledtothebraindamage) when she did.73 The medical evidence did, however, suggest that thedefendant’sbreachhadamorethannegligiblechance of being a cause oftheclaim-ant’sultimatedamageandthisiswhat,erroneously,WallerLJregardedasbeingsufficienttofindliabilityonamaterialcontributiontoinjurybasis.Asaresult,Baileyisaconfused,confusing,andultimatelyunhelpfuldecision.

Medical Negligence

Theperformanceofamaterialcontributiontoinjuryanalysisrequiresparticularcareinsituationsinvolvingmedicalnegligence.Themedicalcontextprovides,inanyevent,a specialkindofchallenge for thecausal inquirybecause,almostbydefinition,medicalpractitionersdealwithindividualswhoarealreadyinjuredordamagedinsomeway.Often,itisthetaskofextricatingthebreachfromthenon-breachfactorswhichmakesthisareaofthelawsodifficult.Anaddeddimensionto thisproblemis the fact thathumanphysiology isunpredictable, imperfectlyunderstoodandoftenmakesitveryhardtodeterminewheretheeffectofonefac-torendsandanotherbegins.

73 ForanAustralianperspective,seeTubemakers of Australia Ltd v Fernandez(1976)50AJLR720(HCA)at724.

110 Material Contribution to Injury

Wright v Cambridge Medical Group providesanexampleofthesedifficulties.74 Inthiscase,theclaimant’sGP,whoworkedforthedefendantpartnership,wasconsultedbytheclaimant’smotherbytelephone,andsubsequentlyfailedtoseetheclaimantortoreferhertohospitalas(thedefendantsconceded)heshouldhavedone.Theclaimant,whowas11monthsold,wasactuallysufferingfromabacterialsuper-infectioncontractedduringanearliervisittohospitalforchickenpox treatment. She was finally referred to hospital two days later. Once there,however,shereceivedinadequatemedicalcare,whichwoulddoubtlesshavebeendeemedtobeinbreachofdutyhadthehospitalbeenjoinedasadefendanttotheactionwhich,inexplicably,itwasnot.Thecausalquestionforthecourt,therefore,was whether the GP’s breach of duty was causative of the claimant’s ultimateinjury (apermanentlyunstablehip, restrictedmovement range, leg lengthdis-crepancyandrestrictedmobility).Ithadtoconsiderwhetherthehospital’sinad-equatetreatmentbrokethechainofcausationbetweenthedefendant’sbreachandtheclaimant’sinjury,andwhetheritwouldbereasonabletohold,asthetrialjudgehaddone,thatevenatimelyreferralwouldhavemadenodifferencetotheclaim-ant’sposition,sincethehospitalwouldhavetreatedherinadequately,leadingtoherinjuriesoccurringinanyevent.

Ultimately, the Court of Appeal (Elias LJ dissenting) allowed the claimant’sappealandfoundthedefendantsliableinfullfortheclaimant’spermanentdam-age.75TheessentialbasisofthisdecisioncanbefoundinthejudgmentofLordNeubergerofAbbotsburyMR:

Inthepresentcase,Iconsiderthatthedefendants’negligencewasacausativefactoroftheclaimant’spermanentinjury.Inotherwords,asinRahman’scase[2001]QB351,para34,Ihaveconcludedthatthenegligenceofthedefendantsandthefailingsofthehospitalhada‘synergisticinteraction,inthateachtendstomaketheotherworse’,andaccordinglyitseemsappropriatetoproceedonthebasisthatbothwerecausativeofthedamagesufferedbytheclaimant.

Idonotconsiderthehospital’sfailuretotreattheclaimantproperlyonceshewasadmitted...wasofsuchsignificancethatitjustifiesafindingthatthedefendant’sneg-ligencewasnotcausativeoftheclaimant’sinjury–orindeedafindingthatitbrokethechainofcausationbetweenthedefendant’snegligenceandtheclaimant’sinjury.Itwasnotsuchanegregiousevent,intermsofthedegreeorunusualnessofthenegligence,ortheperiodoftimeforwhichitlasted,todefeatordestroythecausativelinkbetweenthedefendant’snegligenceandtheclaimant’sinjury.76

Althoughtherewasnomentioninanyofthemajorityjudgments77ofamaterialcontributiontoinjuryanalysis,thefactsofthecasemeantthatthiswouldhave

74 Wright v Cambridge Medical Group[2011]EWCACiv669,[2013]QB312.75 Althoughitalsomadethepointthatthepainandsufferingenduredbytheclaimantafterthetime

ofthenegligencebutbeforehereventualadmissiontohospitaldidnotformpartoftheultimateper-manentdamage,andthedefendantsshouldnotthereforebeliableforit.See[2011]EWCACiv669,[2013]QB312at[52]–[53]328and[92]336–37.

76 [2011]EWCACiv669,[2013]QB312at[36]–[37]325(perLordNeuberger).77 EliasLJreferstoitimplicitly,see[2011]EWCACiv669,[2013]QB312at[92]336–37andexplic-

itlyat[96]337–38.

Medical Negligence 111

beenappropriate: theclaimant’spermanentdamagewas indivisible, thereweremultiplepotentialfactors,andthiswasnotacaseofduplicativecausationbecauseofthelackofsimultaneityandtheinterdependenceoftheeffectsofthosefactors(meaningthattherewasnoseveralsufficiency).78Itshouldhavefallen,therefore,toestablish,asthefinalpartofthejigsaw,whetherthedefendant’sbreachofdutyhad,onthebalanceofprobabilities,beenapart-causeofthatdamage.TheCourtdecidedithad,butitwasaconclusionnotcouchedinmaterialcontributiontoinjuryterms.So,whilsttheCourtofAppeal’sanalysisandonebasedonmaterialcontribution to injury would have led to the same outcome, use of the latterapproachwouldprobablyhaveledtothecasebeingmoreeasilyalignedwiththelineofauthoritytowhichitbelongs.Inanyevent,onanNBA,thesameansweriseasilyreached.

1 – Is it more likely than not that a defendant’s breach of duty changed the claimant’s normal course of events so that damage (including constituent parts of larger damage) occurred which would not otherwise have happened when it did?

ThisquestioniseasytoansweronthefactsofWright becauseitwasclearontheevidencethat,intheabsenceofbothbreaches,theclaimant’sdamagewouldnothaveoccurredwhenitdid.

2 – Was the effect of this defendant’s breach operative when the damage occurred?

Thiswaslesseasytoanswerthanthefirstbecauseoftheinterdependenceofthefactorsinthiscase.Thedefendant’sbreachofdutyandtheconsequentfailureofthe hospital to diagnose and treat Wright accordingly were interdependentbecause,first,itwasnotpossibletosaythat,hadthedefendantmadethereferralatthecorrecttime,thehospital’streatmentwouldhavebeenasbadasitwaswhenthereferralwaseventuallymade.Theremight,forinstance,havebeenmorecom-petentstaffavailableontheearlierday.Infact,giventhattheclaimantshouldhavebeenreferredonaWednesday,butwaseventuallyreferredonaFriday,andthattheCourtfoundthereweremoreconsultantsavailableduringtheweekthantherewereonweekends,theeffectsofthedefendant’sfailuretoreferappearlikelytohavecontinued,andoperatedincombinationwiththosecreatedbythehospital’spoor treatment.79 Secondly, it was generally accepted on the evidence that theclaimant’sdamagebecamepermanentaftersixdaysofinsufficienttreatment.Hadthedefendantmadeanearlierreferral,therefore,thehospitalwouldhavehadalarger ‘window’duringwhich to reachaproperdiagnosis andbegin treatmentaccordingly.Moreover,LordNeubergeralsomadethepointthat

thejudge’sconclusiondidnottakeintoaccounttheagreedexpertevidence...which,infairnesstohim,seemstohavebeenoverlookedintheargumentbeforehim(and,indeed, the argument before us). In my judgment, the effect of that evidence is to

78 SeeCh4,undersub-heading‘SeveralSufficiency’.79 See[2011]EWCACiv669,[2013]QB312at[68]331and[72]332.

112 Material Contribution to Injury

establish,atthelowest,thatitismorelikelythannotthatanypermanentdamagetheclaimantwouldhavesufferedduetotheinepttreatment,whichthejudgefoundthatshewouldhavereceivedifshehadbeenreferredon15April[theWednesday],wouldhavebeensignificantlylessthanthatwhichshedidsuffer.Indeed,Ithinkthatthisevidenceestablishedthatthereisareasonablechancethatshewouldhavesufferedrelativelylittlelong-term damage if she had been referred in the late afternoon or early evening of 15April.80

Whentheclaimant’sdamagebecamepermanent,theriskcreatedbythedefend-ant’sbreachwasstilloperative.81Itisclear,therefore,whyLordNeubergerconsid-eredtheeffectsofthetwofactorstohavebeenoperatingsynergistically.Asafactorwhichpartiallycontributedtherebytoanindivisibleinjury,thebreachofdutywasrightlyheldtobealegallyrelevantcauseandthedefendantliableforfulldamages.Hadthehospitalbeenjoinedasadefendant,itwouldhavebeenappropriatefortheCourttohaveheldbothpartiesjointlyandseverallyliable,sincebothwouldhavemateriallycontributedtotheclaimant’sinjury.

Itisworthre-emphasisingapointalreadymadeinChapter4onDuplicativeCausation.LikethecaseofElayoubi82 mentionedthere,83 Wrightisacaseproperlycategorisedasoneinvolvingamaterialcontributiontoinjurybecausethemultiplefactorsthereinwerenotindependentfromoneanother.If,however,theGP’sfail-uretoreferinWrighthadinnowayaffectedthetreatmentprovidedbythehospi-tal,andifthedelayhadmadenodifferencetotheultimateoutcome,thefactorswouldhavebeenindependent,whichwouldhavemadethecaseoneofpre-emptedcause.Hadthisbeenthecase,thedefendantswouldnothavebeenliablebecausethesecondstageoftheNBAwouldnothavebeensatisfiedinrelationtoit:theeffectsofitsbreachwouldnoteverhaveaffectedtheclaimant,sincetheywouldhavebeenpre-emptedbytheeffectsofthehospital’ssub-standardtreatment.Itiseasytosee,therefore,howsignificantinteractionbetweenfactors(orlackofit)canaffecttheoutcomeofthecausalinquiry.

AmaterialcontributiontoinjuryanalysisisalsoappropriatetotheharrowingfactsofParoline v United States et al.84 Althoughacaseprincipallyaboutcriminalrestitution in the US,85thejudgmentmakessignificantreferencetocausationintortlaw.Theclaimantinthatcasehadasayounggirlbeenthevictimofsexualabuse,whichhadbeenfilmedanddistributedextensivelyonline.Herhurtandhumiliation were therefore set to continue into the future, as more and more individualswitnessedthematerialontheInternet.Thedefendant,whilstnottheindividualwhoproducedthematerialorfirstputitintocirculation,waschargedwithpossessingchildpornography,includingimagesoftheclaimant,andtheUSSupremeCourtwasaskedtoconsider

80 [2011]EWCACiv669,[2013]QB312at[73]332(perLordNeuberger).81 [2011]EWCACiv669,[2013]QB312at[65]–[79]330–34(perLordNeuberger).82 Elayoubi v Zipser[2008]NSWCA335.83 SeeCh4,textton134.84 Paroline v United States et alNo12-8561,April23,2014(USA).85 UndertheViolenceagainstWomenAct1994.

The ‘Doubling of the Risk’ Test 113

the theoryof ‘aggregatecausation,’one formulationofwhichfinds factualcausationsatisfiedwhereawrongdoer’sconduct,thoughalone‘insufficient...tocausetheplain-tiff’sharm,’is,‘whencombinedwithconductbyotherpersons,’‘morethansufficienttocausetheharm.’1Restatement(Third)ofTorts:LiabilityforPhysicalandEmotionalHarm§27,Commentf.86

Sincetheclaimant’smentaldistress,aswellasherneedforongoingcounsellingandlostincome,amountedtoindivisibledamage,andsincetheactofeachindi-vidualviewingthematerialcontributedtothatdamageinaninterdependentway,thiswasacaseinwhichthedefendanthadmateriallycontributedtotheclaimant’sinjury.87

The ‘Doubling of the Risk’ Test88

Cases classified as those in which a defendant has materially contributed to aclaimant’sinjuryarejustoneoftheinstancesinwhichanapplicationofthe‘dou-blingoftherisk’(DTR)testhasbeenmooted.Thistest,conceivedasanepide-miologicaldevice,performsaveryspecificfunction,andhasunfortunatelybeenmisappliedinaforensiccontextseveraltimes.ThefollowingexcerptfromNovartis Grimsby Ltd v Cookson89exemplifiesafactualphenomenonwhichisparticularlycommonincasesinwhichtheclaimant’sdamagetakestheformofadisease.

Besidestheoccupationalexposuretoaromaticaminesinthedyestuffsindustry,whichhasbeenrecognisedasacauseofbladdercancerformanyyears,itisalsoknownthatcigarettesmokingcanbeacause,ascantheingestionofcertaindrugs.Morethanonepotentialcausewaspresentinthiscase.AswellasworkingfortheAppellantformanyyears,MrCooksonhadbeenamoderatecigarettesmoker(10to20aday)forabout20years.Hehadgivenupthehabitinabout1980.Hehadalsotakenpotentiallyharmfuldrugsforatimebutitwasnotsuggestedbyeithersidethatthosedrugshadhadanysignificant effect on the causation of his bladder cancer. Cigarette smoke containsamines and the amines from both sources act on the body in the same way. It wasaccepted by both sides that the two forms of exposure would have had at least an additive,ifnotmultiplicative,effect.Theargumentbetweenthepartieswasabouttherelativepotencyoftheeffectsofsmokingandoccupationalexposure.Inessence, theargumentwaswhethertheoccupationalexposurewassufficienttohavecausedormate-riallycontributedtothedevelopmentofthecancer.90

86 No12-8561,April23,2014(USA)atB.87 Thedefendantinthatcasewasnotheldliableforalloftherestitutionclaimedbythedefendant.

Instead,theCourtattemptedtoestablishwhatwasthedefendant’srelativecausalcontribution–seeNo12-8561,April23,2014(USA)atB.

88 WiththankstoMarkInghamforcheckingthestatisticalaccuracyofwhatfollows.89 Novartis Grimsby Ltd v Cookson[2007]EWCACiv1261,[2007]AllER(D)465(Nov).90 [2007]EWCACiv1261,[2007]AllER(D)465(Nov)at[44](perSmithLJ).

114 Material Contribution to Injury

Theessenceoftheissuefromaforensicpointofviewisthattherearenotonlymultiple potential causes, but that those causes might operate synergistically,ratherthanindependently.‘Interactioniscommon,andexposuresthatsimulta-neouslyprotectagainsttheeffectofotherexposureswhentheycauseadiseasearerare’.91

Thesignificanceofsuch‘synergistic’effectshasunfortunatelybeenexaggeratedinsomerecentdecisions,andattemptstoapplytheDTRtesttodealwiththeper-ceivedproblemaremisguided.ThepracticeappearstohavestartedinSmithLJ’sjudgment in Novartis. As far as the extract above goes, the issue was correctlyidentifiedbutitisnotclearthattheDTRtestwasinanywaydeterminativeof,ornecessaryfor,theresult:

Theevidence...wasthatoccupationalexposureaccountedfor70%to75%ofthetotal.Putintermsofrisk,theoccupationalexposurehadmorethandoubledtheriskduetosmoking.Inmyview,if...thecorrecttestforcausationinacasesuchasthisisthe‘butfor’testandnothinglesswilldo,thattestisplainlysatisfiedonthefactsasfound.Thenaturalinferencetodrawfromthefindingoffactthattheoccupationalexposurewas70%ofthetotalisthat,ifithadnotbeenfortheoccupationalexposure,theRespondentwouldnothavedevelopedbladdercancer. In termsofrisk, ifoccupationalexposuremorethandoublestheriskduetosmoking,itmust,asamatteroflogic,beprobablethatthediseasewascausedbytheformer.92

Evenwithoutanyconsiderationofwhetherariskhadbeendoubled,itseemslikelythatthedefendantinNovartis would have been held liable, on the basis that the occupationalexposureaccountedfor70–75percentofthetotalriskinvolved.93 Thisisstrongevidenceonwhichatribunalcouldbaseabeliefprobability94 that theoccupationalexposurewasmorelikelythannottohavepart-causedthecancerand so formedamaterial contribution to the claimant’s injury.Given that theDTR testwas irrelevant to that result, therefore, itwasunfortunate that itwasmentionedatallbecausethe‘test’issimplynotindependentlydeterminativeofButForcausation;itmerelyprovidesoneindicationofapotentialstatisticalasso-ciationbetweenagivenfactorandagivenresult.95 Sadly, however, the Novartis decisionhasledtotheDTRtestbeingeitherappliedorrequestedinother,equallyunsuitable, contexts since. It was, for instance, applied in Shortell v BICAL Construction,96andreceivedjudicialacceptanceatsomepoint(albeitinbothcases

91 ABroadbent,‘EpidemiologicalEvidenceinProofofSpecificCausation’(2011)17Legal Theory 237,259.

92 [2007]EWCACiv1261,[2007]AllER(D)465(Nov)at[74](perSmithLJ).93 AlthoughtheCourtofAppealdecisioninAB v Ministry of Defence [2012] UKSC 9, [2013] 1 AC

78at[153]135(perSmithLJ)suggestsat[153]thattheDTRtestwasinfactdeterminativeofthiscase,suchanapproachis,withrespect,notthemosthelpfulanalysisoftheevidencetherein.

94 SeeCh2,underheading‘TheBalanceofProbabilities’.95 CMcIvor,‘The“DoublestheRisk”TestforCausation’inSPitel,JNeyersandEChamberlain(eds),

Tort Law: Challenging Orthodoxy (Oxford,HartPublishing,2013).96 Shortell v BICAL Construction,LiverpoolDistrictRegistry(unreported)16May2008.Thedefend-

ant’semployeehaddiedfromlungcancer,havingbeenexposedatworktoasbestosandhavingbeenasmokerforanumberofyearsofhislife.Onthebasisthattheexposuretoasbestosmore than doubled theriskofcontractinglungcancer,MackayJfoundfortheclaimant.

The ‘Doubling of the Risk’ Test 115

bythesameperson)inboththeCourtofAppealinSienkiewicz v Greif 97 and AB v Ministry of Defence.98

Asthenamesuggests,theDTRtestpurportstoequateafindingthatafactorhadtheeffectofexposingaclaimanttotwicetheriskofsufferingdamage,relativetoaclaimant not exposed to that factor, with a finding of probable causation. It istraceabletoMackayJ’sjudgmentinXYZ v Schering.99Thatcase,however,posedahighly specific question, expressly concerned with relative instances of injury. InSienkiewicz v Greif,adecisionwhichsuggestsanappropriatelimitationontheuseoftheDTRtest,LordPhilipsrecognisesthisfact:

XYZ v Schering Health Care Ltd70BMLR88isalengthyandcomplexjudgmentdevotedexclusivelytoapreliminaryissueontheeffectofepidemiologicalevidence.Theissuewaswhetherasecondgenerationoforalcontraceptivesmorethandoubledtheriskofcausingdeepvein thrombosis (DVT) thatwascreatedby thefirstgenerationoforalcontraceptives. It was common ground that, if the claimants in this group litigationcould not establish this, their claims under the Consumer Protection Act 1987 weredoomedtofailure.IdonotbelievethatSmithLJhascorrectlyidentifiedtherelevanceofthisissue.Itwasnot whether the DVT suffered by the claimants had been caused by the secondgenerationoforalcontraceptiveswhichtheyhadtaken.Itwaswhetherthesec-ondgenerationofcontraceptivescreatedasignificantlygreaterriskthanthefirst.Theexpertsappeartohavebeeninagreementthatthe‘doublestherisk’testwastheproperonetoapplyinordertoresolvethisissue.ThusIdonotbelievethatthatdecisionaffordsanydirectassistancetothequestionofwhetherthe‘doublestherisk’testisanappropri-ate test for determining causation in a case of multiple potential causes. (Emphasisadded)100

Inotherwords,theexplicitquestionfortheCourtinXYZ,aproductliabilitycase,waswhethertheproductwhichhadbeenprescribedfortheclaimantswasmorethantwiceaslikelyasitsearlierincarnation(therisksofwhichtheclaimantsweretakentohaveaccepted)tocauseitsusersharm.Here,askingwhethertheriskhasbeendoubledisclearlyanddirectlyappropriatebecause itanswersthisspecificquestion.AsLordPhilipsidentifiedinSienkiewicz,however,thisisnotthesameasaskingwhetheritismorelikelythannotthatoneofseveralpotentialfactorscausedaparticularinjury,andhisLordshipwascorrectinrulingthattheDTR‘test’isnot,therefore,thecorrectapproachtotakeonthosefacts:101

ForreasonsthatIhavealreadyexplained,Iseenoscopefortheapplicationofthe‘dou-blestherisk’testincaseswheretwoagentshaveoperatedcumulativelyandsimultane-ouslyincausingtheonsetofadisease.InsuchacasetheruleinBonnington applies.Where thedisease is indivisible, suchas lungcancer,adefendantwhohas tortiouslycontributedtothecauseofthediseasewillbeliableinfull.Wherethediseaseisdivisible,

97 Sienkiewicz v Greif[2009]EWCACiv1159,[2010]QB370at[23]379(perSmithLJ).98 AB v Ministry of Defence [2012] UKSC 9, [2012] 1 AC 78 at [132] 130, [140] 132, [146] 134, [151]

135,and[153]135.99 XYZ v Schering[2002]EWHC1420,70BMLR88(QB).

100 [2011]UKSC10,[2011]2AC229at[74]261–62.101 SeealsoJStapleton,‘FactualCausation,MesotheliomaandStatisticalValidity’(2012)128LQR

221,223.

116 Material Contribution to Injury

suchasasbestosis,thetortfeasorwillbeliableinrespectoftheshareofthediseaseforwhichheisresponsible.102

With respect, whilst his Lordship’s conclusion is undoubtedly correct on thispoint, the reasonshegivesareneithercompletenor fullyaccurate. Inorder tounderstandwhy,thefunctionofthisepidemiologicaltoolmustbefullyunder-stood.103TherearetwoprincipalreasonswhytheDTRtestisnot,withoutmore,anappropriatedeviceforcalculatingprobabilityofcausation.Thefirstisthattherelative ‘risk’onwhichit isbasedisnot inanytechnicalsenseariskatall,butmerelyameasureofincidenceoveradefinedpopulation:

[I]tiscrucialtorealizethat‘risk’inthiscontextmeansnothingmorethanincidenceoveraspecifiedtimeinterval.Itdoesnotdenotetheproductoftheprobabilitythattheharmwilloccurandthegravityofthatharm;infactitdoesnotevendenoteaprobabil-ity,strictlyspeaking...Itisapurelystatisticalmeasureoftherelativefrequencywithwhichadiseaseoccursinexposedandunexposedpopulations.104

Totreatitassubstitutiveforprobability,therefore,istoconfusetwodistinctcon-cepts,withpotentiallyadverseconsequencesforthecausalinquiry.

The second reason is that the result reached by the relative risk calculationinvolvedgivesa‘netresult’.Thatis,ittellsushowmanyextra casesofadiseasearecaused by the factor being tested. It does not, therefore, include those cases inwhichtheadverseoutcomewouldhavehappenedanyway,justnotwhenitdid.Inotherwords,itonlyidentifiescaseswhichwouldnever otherwise have happened, anddoesnotaccountforthosewhichthefactormerelyaccelerated.Thisissig-nificantsince,aswehaveseenabove,105sufferinginjurysoonerratherthanlaterisundoubtedlydamageforwhichthelawshouldprovidecompensation.

To illustrate this point, Alex Broadbent has provided a simple and effectiveexample:

Consider,forexample,afictitiousgroupofHimalayanporters.Onemightimaginethatcarryingheavyloadsupanddownmountainsincreasestheirriskofbackinjury.Amongthoseporterssufferingbackinjurywillbesomewhoforanatomicalreasonswouldhavedevelopedabackinjuryanyway.Buthavingaweakbackdoesnotprotecttheseportersfromtheeffectsofcarryingheavyloads.Onthecontrary,itisquitepossiblethatcarryingaheavyloadwillbeacauseofbackinjuryamongmanyorevenallthoseporterswhosebacksweresuchthattheywouldhavedevelopedabackinjuryeveninalessphysicallydemandingprofession.[Equatingrelativeriskincidencewithprobabilityofcausation]amountstoendorsingtheastonishingviewthatapersonwhowoulddevelopadiseasewithouttheexposureinquestionistherebyprotectedfromtheeffectsofthatexposure:thathavingaweakbackwillprotectaHimalayanporterfromtheharmthatcarryinga

102 [2011]UKSC10,[2011]2AC229at[90]265.103 Forahighlyusefulaccount,specifictoitsuseinnegligence,seeMcIvor,‘The“DoublestheRisk”

Test’,aboven95.Therealsoexiststhequestionofhowfarsuchepidemiologicalevidenceisrelevanttothecausalinquiryinnegligence,andwhatitslimitsare.ThiswillbeaddressedinCh7.

104 Broadbent,‘Epidemiologicalevidence’,aboven91at240.105 See also Smith v Leech Brain[1962]2QB405(QB)at413(perLordParkerCJ).

The ‘Doubling of the Risk’ Test 117

heavyloadwouldotherwisedotohisback.Itdoesnottakeanygreatconceptualsophis-ticationtoseethatthisisanerror.106

WhatthisdoestellusisthattheDTRtestandthemeasuresonwhichitreliescanunderestimate a factor’s effectonapopulation.What it cannotdo,however, isoverestimatethateffect:

The...problemisthattheexposuredoseatwhichtheprobabilityofcausationexceeds50%(thepointatwhichexposurecausationismorelikelythannot)mayfallwellbelowthe‘doublingdose’(thedoseatwhichtheincidenceofthediseaseisdoubled)...Whenaneffectofexposureistoacceleratethetimeatwhichdiseaseoccurs,theratefraction107 . . .will tend tounderestimate theprobabilityof causationbecause itdoesnot fullyaccountfortheaccelerationofdiseaseoccurrence.Inparticular,andcontrarytocom-monperceptions,aratefractionof50%[whichequatestoafindingthatthe‘risk’hasbeendoubledbythefactorinquestion]108doesnotcorrespondtoa50%probabilityofcausation.109

Theconclusion,therefore,thattheincidenceofinjuryhasbeendoubledbythefactorbeingtestedamountstoasingleindicationthattheremightexistastatisticalassociationbetweenthatfactorandtheinjury.110Itshouldalsobeclear,however,thatthisisnotthesamethingasestablishingonthebalanceofprobabilitiesthatthefactorcausedtheinjury:first,suchaconclusiondoesnotamounttoa ‘factprobability’of50percentormoreandsecond,forreasonsexaminedelsewhereinthisbook,factprobabilitiesarethemselvesnotindependentlysufficienttoestab-lishcausationinnegligence.111Rather,suchstatisticsarejustonecomponentoftherangeofevidenceonwhichacourtreachesitsdecision,and,eo ipso,tellusnothingabout what happened in this particular case.Wrightisinsistent,forexample,thatnon-particularised statistics are ‘mere ad hoc distributions not related to any

106 Broadbent,‘EpidemiologicalEvidence’,aboven91at256.107 Thatproportionofthetotalityofdiseasewithinapopulationwhichisattributabletothefactor

beingtested([incidencerateamongexposedpopulationminus incidencerateamongnon-exposedpopulation]dividedbyincidencerateamongexposedpopulation).

108 Forexample,supposethat40%ofthoseexposedtobrickdustgetdermatitisand20%ofthosenotsoexposedsufferthesamefate.Onthesefigures,itiseasytoseehowtheincidenceor‘risk’isdou-bledbyexposureandhow50%ofcasesareattributabletoexposure,whichiswhatGreenland’s‘ratefraction’ refers to. For a more detailed account of the relationship between the two measures, see A Broadbent, Philosophy of Epidemiology (Basingstoke,PalgraveMacmillan,2013)ch3.

109 S Greenland, ‘Relation of Probability of Causation to Relative Risk and Doubling Dose: AMethodologyErrorThatHasBecomeaSocialProblem’(1999)89American Journal of Public Health 1166,1166and1168–69.See, for instance, Jones v Secretary of State for Energy and Climate Change [2012]EWHC2936(QB),[2012]AllER(D)271(Oct).

110 Conditionallanguageisemployedheredeliberatelytoaccountforallofthepotentialerrorstowhichsuchaconclusionisinanyeventvulnerable,suchaspoorlydesignedexperimentsandsamplingerrors (bothofwhichare independentdangers– seeDBarnes,‘TooManyProbabilities: StatisticalEvidenceofTortCausation’(2001)64Law and Contemporary Problems191).ThisisatopiconwhichtherehasbeenextensiveacademicdiscussionintheUSinparticular:forbothacontributionanda briefreviewofsomeofthearguments,seeMDGreen,‘TheFutureofProportionalResponsibility’in SMadden(ed),Exploring Tort Law (NewYork,NY,CUP,2005).

111 See, for instance, discussion of belief probabilities in Ch 2, under heading ‘The Balance ofProbabilities’.

118 Material Contribution to Injury

causalgeneralisation’.112Indeed,thefallacyofequatingthesetoconclusionsaboutindividualised instancesof causation isnowwellknown, thanks to the famousexamplesofthetaxicabproblem113andtheGatecrasherparadox.114

Broadbent,however,hasdifferentconcerns:

Therearetwoseriousmistakesinjudicialandacademicliteratureonthistopic.ThefirstisthatRR>2isnecessaryforproofofspecificcausation.115Thesecondisthatepide-miologicalevidenceisneversufficientforproofofcausation:thatnomatterhowstrongtheevidenceforageneralcausallinkbetweenawrongandaharm,wearenevertherebywarrantedindecidingthataparticularclaimant’sharmwascausedbythewrong.Botherrorshaveledtoinjustices...ifepidemiologicalevidenceisnotcapableofbearingonindividualcasesthenitwouldleadtotheradicalmisuseofevidencethatisclearlyadmis-sible, such as that generated by medical tests. It follows that, where epidemiologicalevidencetotheeffectthatRR>2istheonlyevidence,itiscapableofprovingcausationasmore likelythannot . . .116Whatepidemiologicalevidencecannotdo,however, isdisproveacausalclaimwhereRR<2.117

Inreferringtothesituationinwhichepidemiologicalevidenceisthe‘only’evi-denceavailable,BroadbentdrawsattentiontoanareainwhichWright’shostilitytotheindependentinfluenceofsuchevidencerequiresthemostscrutiny.118Ifallacourthasatitsdisposalisthatwithwhichepidemiologyprovidesit,shoulditusethisasabasisforitsdecision?ThefollowingextractfromoneofWright’searliestandmostcomprehensiveworksoncausationsuggeststhatthereislessdisagree-mentonthispointthanmightfirstappear:

112 RWright,‘ProvingCausation:ProbabilityvBelief ’inGoldberg(ed)Perspectives on Causation, aboven44at210.

113 Inwhichanindividualisknockeddownbyataxiwhosecolourisnotobserved.Theincidentoccursinatownwherethereareonlytwotaxifirms:onewhichhasthreebluecabs,andanotherwhichhasoneyellowcab.Theexampleissupposedtoshowthatitwouldbeinappropriatetoinferfromthosefactsalonethatitwasmoreprobablethannotthattheaccidentinvolvedabluecab,despitetheexistenceof a 75% statistical probability of this. The example can be found in the dissenting judgment ofBrachtenbachJinHerskovits v Group Health Cooperative of Puget Sound664P2d474(Wash1983),adecisionoftheSupremeCourtofWashington.Amorecomplexexample,towhichparticularisticevi-denceandreliabilityestimateshavebeenadded,canbefoundinATverskyandDKahneman,‘EvidentialImpactofBaseRates’ inDKahneman,PSlovicandATversky(eds),Judgement Under Uncertainty: Heuristics and Biases(Cambridge,CUP,1982)153.SeealsoCh7.

114 Inwhichthereisarodeowith1,000attendees,499ofwhomhavepaidforadmission.Therearenoissuedtickets,nortestimonyastowhetherAclimbedoverafencetogainentry.Thereis,however,amathematicalprobabilityof.501thatAdidnotpay,whichwouldmean,onamathematicalinterpre-tationof theforensicstandard, that theorganiserswouldbeentitledto judgmentagainsthim.Theproblemhereisthattheywouldalsobeentitled,onthosegrounds,tojudgmentagainsteveryattendeeonthesamebasis.LJCohen,The Probable and the Provable (Oxford,OUP,1977)75.

115 Thisreferstothedistinctionsometimesmadebetweenthequestionofwhetheranagentiscapa-bleofcausingan injuryof the type inquestion(generalcausation)and thequestionofwhetheraparticular claimant’s injury was caused by a particular defendant’s breach (specific causation). SeeSeltsam Pty Ltd v McGuiness(2000)49NSWLR262(NSWCA)at[22](perSpigelmanCJ).

116 Sincecourtshavetomakeadecisiononewayoranother,anyrelevantevidenceiscapableofhelp-ingtoreachabeliefprobability.

117 Broadbent, Philosophy of Epidemiology,aboven108at206.Chapter7willelaboratefurtheronthegeneralapplicabilityofepidemiologicalevidencetotheforensicexercise.

118 SeeMDGreen,‘TheFutureofProportionalLiability:TheLessonsofToxicSubstancesCausation’inMadden(ed),Exploring Tort Law, above n 110 at 352.

The ‘Doubling of the Risk’ Test 119

Ajudgmentonwhatactuallyhappenedonaparticularoccasionisajudgmentonwhichcausalgeneralizationanditsunderlyingcausallawwasfullyinstantiatedontheparticu-laroccasion.Particularisticevidenceconnectsapossiblyapplicablecausalgeneraliza-tion to the particular occasion by instantiating the abstract elements in the causalgeneralization, thereby converting the abstract generalization into an instantiated generalization.Withoutsuchparticularisticevidence,thereisnobasisforapplyingthecausalgeneralizationtotheparticularoccasion.119

Inotherwords,onWright’sanalysis,evidenceofaclaimant’sexposuretoagivenagent is particularised evidence sufficient to link epidemiological informationaboutaconditiontothatclaimant.120 Where this is all that is available,

thentheonlypossiblyapplicablecausalgeneralisationwithatleastsomeparticularisticinstantiationintheparticularsituationisthetoxic-agentcausalgeneralisation,whichfactcouldsupporttheformationofabeliefthatitwasthecausalprocessactuallyatworkintheparticularsituation.121

Wright’s point is not, therefore, that epidemiology cannot be used or useful.Rather,hisentireconceptualisationofcausationdemandsthattherebeadistinc-tionbetween‘mereadhocdistributions’andparticularinstancesofcausation.122 Logically,thismustbecorrect.OnemeansofillustratingthisistoshowhowaRRof<2isequallycompatiblewitha0percentand100percentprobabilityofcau-sation.Greenlanddoesthisusingthefollowingillustration:

Asanextremeexample,supposethedamagedonebyexposurewasthatofacceleratingthedevelopmentofdiseaseinallindividualsdestinedtocontractdisease.Then,whenconsideringthelifetimeexperienceoftheexposedcohort,alloftheexposedoccurrencesofdiseasewouldbeacceleratedcases...Inotherwords...theexcessfractionwouldbe0[andtheRRwouldbe1],incorrectlysuggestingthattherewasnoexposureeffect,andyettheprobabilityofcausationwouldbe100%.123

In conclusion, it would seem that the epidemiological device of estimating theeffectofagivenfactorcanbeforensicallyusefulwherethateffectisshownat least tohavedoubledtheratesofincidenceasagainstbackgroundfactors.Itisequallyclear,however,thatthismethodshouldinnowayconstitutearoutineorstand-alonetestwhichistreatedasconclusiveofthecausalinquiry.124ThedecisionoftheHighCourtofAustraliainAmaca Pty Ltd v Ellis125isanobjectlessoninhowtodeal

119 RWright,‘Causation,Responsibility,Risk,Probability,NakedStatistics,andProof:PruningtheBrambleBushbyClarifyingtheConcepts’(1988)73Iowa Law Review1001,1051.

120 AlthoughseeSienkiewicz v Greif [2011]UKSC10,[2011]2AllER857at[158]906–07(perLordRodger)andat[170]910(perBaronessHale).

121 Wright,‘ProvingCausation’,aboven112atn67.122 See also Sienkiewicz v Greif[2011]UKSC10,[2011]2AllER857at[96]888.123 Greenland,‘Relation of Probability’, above n 109 at 1168. Greenland further points out that,

whilstthesefactsmayseemfarfetched,itispreciselywhatwillbeseeniftheoutcomeinquestionisdeathratesinapopulationfollowedforitsentirelifetime,suchastheatomicbombsurvivorsinJapan.

124 See Seltsam Pty Ltd v McGuiness(2000)49NSWLR262(NSWCA)at[78]–[89]and[102](perSpigelmanCJ).Althoughthiswasamaterialcontributiontoriskcase,thepointremainsrelevantwhat-everthecausalquestion.

125 Amaca Pty Ltd v Ellis[2010]HCA5,(2010)240CLR111.

120 Material Contribution to Injury

appropriatelywithsuchepidemiologicalevidence.126Thedeceasedinthatcasehaddiedfromlungcancer,havingbeenasmokerforover25yearsandalsohavingbeenexposedbythedefendantemployerstoasbestosinbreachoftheirdutyofcare.Appropriately,theHighCourtmadenomentionoftheDTRtest,butinsteadconsideredtheepidemiologicalevidencepresentedtoitasanevidentialcompo-nentinitsinferencefromthefacts127astowhat,onthebalanceofprobabilities,causedthedeceased’scancer:

IftherelativerisksandprobabilitiesderivedfromepidemiologicalstudiesweretobetreatedasrevealingwhatwasaprobableexplanationofwhatcausedMrCotton’scancer,thoseanalysessupporttwoconclusions.First,itismoreprobablethannotthatsmokingwasacauseof(inthesensethatitwasanecessaryconditionfor)MrCotton’scancer.Second,therisksandprobabilitiesassociatedwithasbestos,whetheraloneorincon-junction with smoking, are low and not sufficient to found the inference which theplaintiffsoughttohavemade:thatitismoreprobablethannotthatexposuretorespi-rableasbestosfibreswasacauseofMrCotton’scancer.128

SincethefindingsofliabilityinbothNovartis129 and Shortell130 were based on evi-dencethattherespectivebreachesofdutymore than doubled theriskoftheharmoccurring, the formationofabeliefprobability that thosebreachesmore likelythannotcausedtheinjuriesseemsunobjectionable.131Nevertheless,thepresenta-tionoftheseresultsasbeingpredicatedonsatisfactionoftheDTRtestisregret-table.

Therelativeriskspermitssuchaninferenceonlyifitiscredible,whichmeansthatthebeliefprobabilityisgreaterthanfiftypercent.Thepreponderanceoftheevidencestan-dardisnotmetwithoutabeliefprobabilityofgreaterthanfiftypercentandariskratiogreaterthan2.0.132

Forthereasonsjustoutlined,therefore,courtsshouldrefrainfromaskingexpertstopresenttheirevidence intheformofananswertotheDTRtest,butshouldinsteadensurethat,wherepossible,suchevidencetakesaccountofwhatepidemi-ologists refer toas theetiologic fraction. In essence, this coversboth the excess

126 SeealsoDHamer,‘Mindthe“EvidentialGap”:CausationandProofinAmaca Pty Ltd v Ellis’ (2009)31Sydney Law Review465(criticisingthecontrastingapproachoftheCourtofAppeal).

127 See Clements v Clements[2012]SCC32,[2012]2SCR181at[38](perMcLachlinCJ).128 [2010]HCA5,(2010)240CLR111at[64]134.Thesefactswouldnot,therefore,satisfythefirst

stageoftheNBA:seeabove,textton20.SeealsoEvans v Queanbeyan City Council(2011)9DDCR541,[2011]NSWCA230whichfollowsEllisinallaspectsmaterialtothecurrentdiscussion.InEvans, the CourtofAppealmadeamisleadingandunfortunatereferencetotheFairchildprinciple,insayingthatitcouldnotbeappliedbythem,butwouldbeamatterfortheHighCourt.ThefactsofEvans would not,inanyevent,besuitableforacorrectapplicationofthatprinciple–seeCh6generally,andCh7,n31.

129 [2007]EWCACiv1261,[2007]AllER(D)465(Nov).130 LiverpoolDistrictRegistry,(unreported)16May2008.131 SeealsoJStapleton,‘FactualCausation,MesotheliomaandStatisticalValidity’,aboven101at223

and227foranexplanationofwhytheDTRtestisonlyapplicablewhereconclusionsaresoughtastowhichofseveralmutually exclusive or‘competingalternative’mechanismscausedtheinjuryinques-tion.

132 Barnes,‘TooManyProbabilities’,aboven110at207.

The ‘Doubling of the Risk’ Test 121

fractionalreadyreferredto(thosecaseswhichwouldneverhavehappenedbutfortheexposure)as well asthatfractionofcaseswhichwouldstillhavehappenedbutfor the exposure, but not until later (those accelerated by the exposure). Thispaintsacomprehensivepictureofallofthosecasesaffectedbytheexposure,anddoesnotunderestimateitinthewaythatDTRdoes.133

Toexplaintheprobleminalgebraicterms,supposethatAT

exposedpersonscontractedthe disease during the time period in question and that, of these individuals, A

0 are

unaffected,A1wereacceleratedbyexposure,andA

2representedall-or-noneoccurrences

ofdisease[thosethatwouldnothaveoccurredatallbutfortheexposure].Bydefinition,exposure...harmedpersonswhosediseasewaseitheracceleratedorallornone.Hence,thefractionofexposedpersonswiththediseasewhowereharmedbytheexposureis (A

1 + A

2)/A

T.Thisquantityistheetiologicfraction.Furthermore,ifwerandomlyselect

anexposedpersonwithdiseasefromthetotalAT,thechancethatexposureharmedthat

person(i.e.,thechancethatthepersonhadanacceleratedorall-or-noneoccurrence)isalso(A

1 + A

2)/A

T.Thelatterquantityisthusalsotheprobabilityofcausation.134

In Merrell Dow Pharmaceuticals v Havner,135 the Supreme Court of Texas, in ajudgment referred to with apparent approval by Lord Philips in Sienkiewicz,136 madethemethodologicerrortowhichGreenlandrefers:

Assumethataconditionnaturallyoccursinsixoutof1,000peopleevenwhentheyarenotexposedtoacertaindrug.Ifstudiesofpeoplewhodidtakethedrugshowthatnineoutof1,000contractedthedisease,itisstillmorelikelythannotthatcausesotherthanthedrugwereresponsibleforanygivenoccurrenceofthediseasesinceitoccursinsixoutof1,000individualsanyway.Sixofthenineincidenceswouldbestatisticallyattrib-utabletocausesotherthanthedrug,andtherefore,itisnotmoreprobablethatthedrugcausedanyoneincidenceofdisease.Thiswouldonlyamounttoevidencethatthedrugcouldhavecausedthedisease.However,ifmorethantwelveoutof1,000whotakethedrugcontractthedisease,thenitmaybestatisticallymorelikelythannotthatagivenindividual’sdiseasewascausedbythedrug.137

Thisstatementassumes,ofcourse,thatanyonewhowaseverlikelytohavesuf-feredfromtheconditioninquestionwouldhavebeenimmunetotheeffectsofthedrug(andtherebyfailstorecognisethosecaseswherethedrugwouldacceleratethedevelopmentof thedisease in thosewhowouldhavecontracted itat somepoint).Whilstthisbiologicalpatterncanprobablynotberuledoutaseveroccur-ring, it should certainly not be treated as if it were a normal occurrence. Theexcerptabove,therefore,demonstratesaforensicunderestimationoftheeffectsofthedruginquestion.Thiserrorisunfortunate,notonlyforits intrinsiclogicalflaw,butalsobecauseitdetractsfromadecisionwhichisotherwiseconstructiveinitstreatmentofepidemiologicalevidence(andwhich,anyway,didnotrelyon

133 ItalsoemphasisestheimportanceofthetemporaldimensiontotheButForquestion,asdis-cussedabove.

134 Greenland,‘RelationofProbability’,aboven109at1167–68.135 Merrell Dow Pharmaceuticals v Havner953SW2d706(Tex1997).136 [2011]UKSC10,[2011]2AC229at[85]264.137 953SW2d706(Tex1997)at717.

122 Material Contribution to Injury

thismistakeninterpretationoftheevidenceforitsultimateresultofnoliability).Elsewhere,forinstance,OwenJstates:

Werecognize,asdoesthefederalReference Manual on Scientific Evidence, that a disease orconditioneitherisorisnotcausedbyexposuretoasuspectedagentandthatfre-quencydata, suchas the incidenceofadverseeffects in thegeneralpopulationwhenexposed,cannotindicatetheactualcauseofagivenindividual’sdiseaseorcondition ...Butthelawmustbalancetheneedtocompensatethosewhohavebeeninjuredbythewrongfulactionsofanotherwiththeconceptdeeplyimbeddedinourjurisprudencethatadefendantcannotbefoundliableforaninjuryunlessthepreponderanceoftheevidencesupportscauseinfact.Theuseofscientificallyreliableepidemiologicalstudiesandtherequirementofmorethanadoublingoftheriskstrikesabalancebetweentheneedsofourlegalsystemandthelimitsofscience...Wedonothold,however,thatarelativeriskofmorethan2.0isalitmustestorthatasingleepidemiologicaltestislegallysufficientevidenceofcausation.Otherfactorsmustbeconsidered.Asalreadynoted,epidemiologicalstudiesonlyshowanassociation.Theremayinfactbenocausalrela-tionshipeveniftherelativeriskishigh....Likewise,evenifaparticularstudyreportsalowrelativerisk,theremayinfactbeacausalrelationship.Thestrongconsensusamongepidemiologistsisthatconclusionsaboutcausationshouldnotbedrawn,ifatall,untilanumberofcriteriahavebeenconsidered.138

Thisexcerptformsonlypartofthejudgment’sconsiderableevaluationoftheuseofepidemiologicalevidence,andthevariouswaysinwhichitcanbeinterpretedandused.UnliketheEnglishcaseswhichrelyonepidemiologicaldata,thisdeci-sioncitesmuchacademiccommentaryontheissue,andhighlightspointsofdisa-greement and uncertainty.139 This explains, at least in part, the measured andcautionaryapproachtakenbythecourttotheuseofsuchinformation,anditisunfortunatethattheEnglishcourtshaveinsteadchosentoimplementthespecial-isedDTRtestwithoutanycomparablereferencetoexpertevaluation.

138 953SW2d706(Tex1997)at718.Although theReference Manual referred toalsomakes theinterpretativemistakehighlightedhere,asAlexBroadbentpointsoutinBroadbent,‘EpidemiologicalEvidence’,aboven91at254.See,however,Restatement (Third) of Torts: Liability for Physical Harm§28commentc.

139 953SW2d706(Tex1997)at715–21inparticular.