ORBITAandcoronarystents:

Acasestudyintheanalysisandreportingofclinicaltrials

AndrewGelman,JohnCarlinandBrahmajeeKNallamothu

19Mar2019

DepartmentofStatisticsandPoliticalScience,ColumbiaUniversity,NewYorkCity,NY,UnitedStates(AndrewGelman,professor);ClinicalEpidemiology&Biostatistics,MurdochChildren’sResearchInstitute,MelbourneSchoolofPopulationandGlobalHealthandDepartmentofPaediatrics,UniversityofMelbourne,Melbourne,Australia(JohnCarlin,professor);DepartmentofInternalMedicine,UniversityofMichiganMedicalSchool,AnnArbor,MI,UnitedStates(BrahmajeeKNallamothu,professor);Correspondenceto:BrahmajeeKNallamothubnallamo@med.umich.eduAcknowledgements:WethankDougHelmreichforbringingthisexampletoourattention,ShiraMitchellforhelpfulcomments,andtheOfficeofNavalResearch,DefenseAdvancedResearchProjectAgency,andtheNationalInstitutesofHealthforpartialsupportofthiswork.Competinginterests:Dr.GelmanandDr.Carlinreportnocompetinginterests.Dr.NallamothuisaninterventionalcardiologistandEditor-in-ChiefofajournaloftheAmericanHeartAssociationbutotherwisehasnocompetinginterests.WordCount:3078

1.Introduction

Al-Lameeetal.(2017)reportresultsfromarandomizedcontrolledtrialofpercutaneouscoronaryinterventionusingcoronarystentsforstableangina.Thestudy,calledORBITA(ObjectiveRandomisedBlindedInvestigationWithOptimalMedicalTherapyofAngioplastyinStableAngina),includedapproximately200patientsandwasnotableforbeingablindedexperimentinwhichhalfthepatientsreceivedstentsandhalfreceivedaplaceboprocedureinwhichashamoperationwasperformed.Infollow-up,patientswereaskedtoguesstheirtreatmentandofthosewhowerewillingtoguessonly56%guessedcorrectly,indicatingthattheblindingwaslargelysuccessful.

Thesummaryfindingfromthestudywasthatstentingdidnot“increaseexercisetimebymorethantheeffectofaplaceboprocedure”withthemeandifferenceinthisprimaryoutcomebetweentreatmentandcontrolgroupsreportedas16.6secondswithastandarderrorof9.8(95%confidenceinterval,−8.9to+42.0s)andap-valueof0.20.IntheNewYorkTimes,Kolata(2017)reportedthefindingas“unbelievable,”remarkingthatit“stunnedleadingcardiologistsbycounteringdecadesofclinicalexperience.”Indeed,oneofus(BKN)wasquotedasbeinghumbledbythefinding,asmanycardiologistshadexpectedapositiveresult.Ontheotherhand,Kolatanoted,“therehavelongbeenquestionsabout[stents’]effectiveness.”Attheveryleast,thewillingnessofdoctorsandpatientstoparticipateinacontrolledtrialwithaplaceboproceduresuggestssomedegreeofexistingskepticismandclinicalequipoise.

ORBITAwasalandmarktrialduetoitsinnovativeuseofblindingforasurgicalprocedure.However,substantialquestionsremainregardingtheroleofstentinginstableangina.Itisawell-knownstatisticalfallacytotakearesultthatisnotstatisticallysignificantandreportitaszero,aswasessentiallydoneherebasedonthep-valueof0.20fortheprimaryoutcome.Hadthiscomparisonhappenedtoproduceap-valueof0.04,wouldtheheadlinehavebeen,“‘Believable’:HeartStentsIndeedEaseChestPain”?Alotofcertaintyseemstobehangingonasmallbitofdata.

ThepurposeofthispaperistotakeacloserlookatthelackofstatisticalsignificanceinORBITAandthelargerquestionsitraisesaboutstatisticalanalyses,statisticallybaseddecisionmakingandthereportingofclinicaltrials.ThisreviewofORBITAisparticularlytimelyinthecontextofthewidelypublicizedstatementreleasedbytheAmericanStatisticalAssociationthatcautionedagainsttheuseofsharpthresholdsfortheinterpretationofp-values(WassersteinandLazar,2016).Weendbyofferingpotentialrecommendationstoimprovereporting.

2.StatisticalanalysisoftheORBITAtrial

Adjustingforbaselinedifferences.InORBITA,exercisetimeinastandardizedtreadmilltest—theprimaryoutcomeinthepreregistereddesign—increasedonaverageby28.4sinthetreatmentgroupcomparedtoanincreaseofonly11.8sinthecontrolgroup.Asnotedabove,thisdifferencewasnotstatisticallysignificantatasignificancethresholdof0.05.Hence,followingconventionalrulesofscientificreportingitwastreatedaszero—aninstanceoftheregrettablycommonstatisticalfallacyofpresentingnon-statistically-significantresultsasconfirmationofthenullhypothesisofnodifference.

However,theestimateusinggaininexercisetimedoesnotmakefulluseofthedatathatwereavailableondifferencesbetweenthecomparisongroupsatbaseline(VickersandAltman,2001,Harrell,2017a).AscanbeseenintheTable,thetreatmentandplacebogroupsdifferintheirpre-treatmentlevelsofexercisetime,withmeanvaluesof528.0and490.0s,respectively.Thissortofdifferenceisfine—randomizationassuresbalanceonlyinexpectation—butitisimportanttoadjustforthisdiscrepancyinestimatingthetreatmenteffect.Inthepublishedpaper,theadjustmentwasperformedbysimplesubtractionofthepre-treatmentvalues:

Gainscoreestimatedeffect: (ypost−ypre)T−(ypost−ypre)

C, (1)

Butthisover-correctsfordifferencesinpre-testscores,becauseofthefamiliarphenomenonof“regressiontothemean”—justfromnaturalvariation,wewouldexpectpatientswithlowerscoresatbaselinetoimprove,relativetotheaverage,andpatientswithhigherscorestoregressdownward.Theoptimallinearestimateofthetreatmenteffectisactually:

Adjustedestimate: (ypost−βypre)T−(ypost−βypre)

C, (2)

whereβisthecoefficientofypreinaleast-squaresregressionofypostonypre,also

controllingforthetreatmentindicator.Theestimatein(1)isaspecialcaseoftheregressionestimate(2)correspondingtoβ=1.Giventhatthepre-testandpost-testmeasurementshavenearlyidenticalvariances(ascanbeseenintheTable),wecananticipatethattheoptimalβwillbelessthan1,whichwillreducethecorrectionfordifferenceinpre-testandthusincreasetheestimatedtreatmenteffectwhilealsodecreasingthestandarderror.Asaresult,anadjustedanalysisofthesedatawouldbeexpectedtoproducealowerp-value.

Theadjustedregressionanalysiscanbedoneusingtheinformationavailableinthe

Table,asexplainedindetailinBox1.Thep-valuefromthisadjustedanalysisis0.09:asexpected,lowerthanthep=0.20fromtheunadjustedanalysis.

Alternativereporting.Despitemovingclosertotheconventional0.05threshold,thep-valueof0.09remainsonthesideoftheconventionallevelofsignificancewhereonewouldnotrejectthenullhypothesis.Apotentialblockbusterreversalwithanadjustedanalysis—“StatisticalSleuthsTurnReportedNullEffectintoaStatisticallySignificantEffect”—doesnotquitematerialize.

Yetwithindifferentconventionsforscientificreporting,thisexperimentcouldhavebeenpresentedaspositiveevidenceinfavorofstents.Insomesettings,ap-valueof0.09isconsideredtobestatisticallysignificant;forexample,inarecentsocialscienceexperimentpublishedintheProceedingsoftheNationalAcademyofSciences,Sands(2017)presentedacausaleffectbasedonap-valueoflessthan0.10,andthiswasenoughforpublicationinatopjournalandinthepopularpress,with,forexample,thatworkmentioneduncriticallyinthemediaoutletVoxwithoutanyconcernregardingsignificancelevels(Resnick,2017).Bycontrast,VoxreportedthatORBITAshowedstentstobe“dubioustreatments,”aprimeexampleofthe“epidemicofunnecessarymedicaltreatments”(Belluz,2017).HadAl-Lameeetal.performedtheadjustedanalysiswiththeirdataandpublishedinPNASratherthantheLancet,couldtheyhaveconfidentlyreportedacausaleffectofstentsonexercisetime?

Onealsocouldconsiderotheroptions.Forexample,onecouldjusttakethesummariesfromtheTableandreportthemasfollows:Withstents,thereisastatisticallysignificantimprovementof28.4seconds(witha95%confidenceintervalthatclearlyexcludeszero);withplacebo,thereisnostatisticallysignificantchange.Thus,thedatashowthatstentsworkandplacebohasnoeffect.Suchaconclusionwouldbeinappropriate,asitwouldbemakingtheerrorofcomparingsignificancetonon-significance(GelmanandStern,2006).Butthiserrorappearsinpublishedpapersallthetime,includingintopjournals,soitrepresentsanotherwaythedatacouldhavebeenreported(BlandandAltman2015,Allisonetal.,2016).

OurpointhereisnotatalltosuggestthatAl-Lameeelal.engagedinreverse“p-hacking”(Simmons,Nelson,andSimonsohn,2011),choosingananalysisthatproducedanexplosivenullresult.Infact,theauthorsshouldbecongratulatedforpre-registeringtheirstudyandpublishingtheirprotocolpriortoperformingtheiranalyses.Ratherwewishtoemphasizetheflexibilityinherentbothindataanalysisandreporting—eveninthecaseofacleanrandomizedexperiment.Wearepointingoutthepotentialfragilityofthestents-didn’t-workstoryinthiscase.Existingdatacouldeasilyhavebeenpresented

asasuccessforstentscomparedtoplacebobyauthorswhowereaimingforthatnarrativeandperformingmoreorlessreasonableanalyses.

Fragilityofthefindings.Howsensitiveweretheresultstoslightchangesinthedata?Tobetterunderstandthiscriticalpoint,onecanperformasimplebootstrapanalysis,computingtheresultsthatwouldhavebeenobtainedfromreanalyzingthedata1000times,eachtimeresamplingpatientsfromtheexistingexperimentwithreplacement(Efron,1979).Asrawdatawerenotavailabletous,weapproximatedusingthenormaldistributionbasedontheobservedz-scoreof1.7.Theresultwasthat,in40%ofthesimulations,stentsoutperformedplaceboatatraditionallevelofstatisticalsignificance.Thisisnottosaythatstentsreallyarebetterthanplacebo–thedataalsoappearconsistentwithanulleffect.Thetake-homepointofthisexperimentisthattheresultscouldeasilyhavegone“theotherway,”whenreportingisforcedintoabinaryclassificationofstatisticalsignificance,formanydifferentreasons.

3.Designofthetrialandclinicalsignificance

Inajustificationfortheirstudydesignandsamplesize,Al-Lameeetal.(2017)wrote:“Evidencefromplacebo-controlledrandomisedcontrolledtrialsshowsthatsingleantianginaltherapiesprovideimprovementsinexercisetimeof48–55s...Giventhepreviousevidence,ORBITAwasconservativelydesignedtobeabletodetectaneffectsizeof30s.”Theestimatedeffectof21swithstandarderror12sisconsistentwiththe“conservative”effectsizeestimateof30sgiveninthepublishedarticle.Soalthoughtheexperimentalresultsareconsistentwithanulleffect,theyareevenmoreconsistentwithasmallpositiveeffect.

Onemightask,however,abouttheclinicalsignificanceofsuchatreatmenteffect.,whichwecandiscusswithoutrelevancetop-valuesorstatisticalsignificance.Forsimplicity,supposewetakethepointestimatefromthedataatfacevalue.Howshouldwethinkaboutanincreaseinaverageexercisetimeof21s?Onewaytoconceptualizethisisintermsofpercentiles.Thedatashowapre-randomizationdistribution(averagingthetreatmentandcontrolgroups)withameanof509andastandarddeviationof188.Assuminganormalapproximation,anincreaseinexercisetimeof21sfrom509to530wouldtakeapatientfromthe50thpercentiletothe54thpercentileofthedistribution.Lookedatthatway,itwouldbehardtogetexcitedaboutthiseffectsize,evenifitwerearealpopulationshift.

Beyondexercisetime,therewereothersignalsfromORBITAthatseemedtosuggestconsistentimprovementsinthephysiologicalparameterofischemiathroughendpoints

suchasfractionalflowreserve,instantaneouswave-freeratio,andstressecho.Actually,findingsfromthestressechohighlightapotentiallyimportantavenueintoanalternativepresentationoftheseresults.Thereisnoquestionthatsomephysiologicalchangesarebeingmadebystents,withverylargeandhighlystatisticallysignificant(p<0.001)effectsseenonechomeasures.Asisoftenthecase,thenullhypothesisthatthesephysicalchangesshouldmakeabsolutelyzerodifferencetoanydownstreamclinicaloutcomesseemsfarfetched.Thus,thesensiblequestiontoaskis“Howlargearetheclinicaldifferencesobserved?”,not“Howsurprisingistheobservedmeandifferenceundera[spurious]nullhypothesis?”Thesimpletextbookwaytotacklethisquestionistoreportconfidenceintervals(CIs)aroundthemeandifferencesandnottofocusonwhethertheintervalshappentoincludezero.Thefactthatthestandard95%CIfortheprimaryoutcomecomfortablyincludesthetargeteffectsizeof30ssuggeststhisvalueshouldbenomore“rejected”thanthenullvalue.Furthermore,withoutthelongitudinaldatatoobservetheoutcomesthatmattermosttopatients—healthandlengthoflife—muchremainsuncertain.

Thelargerquestionhastobeaboutbalancingthelong-termbenefitsofstentswithrisksoftheoperation.Itdoesnotseemreasonableforapersontorisklifeandhealthbysubmittingtoasurgicalprocedurejustforapotentialbenefitof21secondsofexercisetimeonastandardizedtreadmilltest—orevenahypothesizedlargerbenefitof50seconds,whichwouldstillonlyrepresenta10%improvementforanaveragepatientinthisstudy.Yetmaybea5-10%increaseisconsequentialinthiscaseasitcouldimprovequalityoflifeforapatientoutsideofthisartificialsetting.Perhapsthissmallgaininexercisetimeisassociatedwiththeneedforlessmedications,fewerfunctionallimitationsorgreatermobility.Ifso,however,onemightpostulatethisgainwouldhavebeenapparentinassessmentsofanginaburden,anditwasnot.

Partofthebiggerconcernhereisthatthesepatientswerealreadydoingprettywellonmedications—thatis,theyalreadyhadalowsymptomfrequencybeforestenting.Forexample,anginafrequencyasmeasuredbytheSeattleAnginaQuestionnairewas63.2afteroptimizingmedicationsandbeforestentinginthetreatmentgroup.Thisroughlytranslatesas“monthly”angina(JohnSpertus,personalcommunication).Howdoesastudywithafollow-upofjust6weeksexpecttoimproveanoutcomethathappensthisinfrequently?Infact,oneofthegreatdebatessurroundingORBITAisthatthosewhodiscountthetrialsuggestitenrolledpatientswhotypicallydonotreceivestentsinroutinepractice.ThosewhobelieveORBITAisagame-changerarguethattheselesssymptomaticpatientsactuallymakeupalargeproportionofthosereceivingstents—andthatiswhywehavesuchalargeproblemwiththeiroveruse.

Finally,arestentsreallybeinggiventopatientswithstableanginajusttoimprovefitnessortoreducesymptoms?Oristhereacontinuedexpectationthatstentshavelong-termbenefitsforpatients,despiteearlierdatafromstudiesliketheClinicalOutcomesUtilizingRevascularizationandAggressiveDrugEvaluation(COURAGE)study(Boden,2007)?Thiswouldseemtobethekeyquestion,inwhichcasetheshort-termeffects,orlackthereof,foundintheORBITAstudyarelargelyirrelevant.Otherlargertrials,suchasInternationalStudyofComparativeHealthEffectivenessWithMedicalandInvasiveApproaches(ISCHEMIA,see:https://clinicaltrials.gov/ct2/show/NCT01471522)areconsideringthismorefundamentalquestionbutwillnothaveaplaceboprocedure.

4.Recommendationsforstatisticalreportingoftrials

Thesearchforbettermedicalcareisanincrementalprocess,withincompleteevidenceaccumulatingovertime.Thereisunfortunatelyafundamentalincompatibilitybetweenthatcoreideaandthecommonpractice,bothinmedicaljournalsandthenewsmedia,ofup-or-downreportingofindividualstudiesbasedonstatisticalsignificance.WeoffersomerecommendationssummarizedinBox2thatwebelievewillbehelpfultoauthorsandeditorsmovingforward.

Atthispointit’snotclearhowbesttoincorporatethisrecentexperimentintoroutinepracticedespiteitsnovelandprovocativestudydesign,sotheforcedreportingoftheprimaryoutcomeas“positive”or“negative”isunhelpful.AreanalysisofthesummarydatafromAl-Lameeetal.(2017)revealsastrongerestimatedeffectthatisclosertotheconventionalboundaryofstatisticalsignificance,indicatingthatthestudycouldrathereasilyhavegeneratedandreportedevidenceinfavorof,ratherthanagainst,theeffectivenessofstentsforpatientswithstableangina.Andfromourbriefflurryofexcitementoverthepossibilitythatasimplereanalysiscouldchangethesignificancelevel,weareagainremindedofthesensitivityofheadlineconclusionstodecisionsinstatisticalanalysis.Inanycase,though,theobservedincreasesinexercisetime,evenifstatisticallysignificant,donotappearatfirstglancetobeofmuchclinicalimportance,comparedtothemuchmorerelevantlong-termhealthoutcomesthatremainuncertain.

Inthedesign,evaluation,andreportingofexperimentalstudies,thereisanormoffocusingonthestatisticalsignificanceofaprimaryoutcome–inthiscase,changeinaverageexercisetimeonastandardizedtreadmilltest.Ingeneral,theresultingconclusionswillbefragilebecausep-valuesareextremelynoisyunlesstheunderlyingeffectishuge.Anexperimentmaybedesignedtohave80%power,butthisdoesn’teliminatethefragility,asillustratedbyourbootstrapre-analysis.Itisalsooftenconditionalonanoverestimatedeffectsize(SchulzandGrimes,2005,Gelman,2018)

anddoesnotaddresstheimportantquestionofvariationintreatmenteffects.ExaminationoftheLancetpaperanditsreceptioninthenewsmediasuggeststhatitexhibitsaclassiccaseof“significantitis”or“dichotomania”(Greenland,2017),withfrequentrepetitionofphrasessuchas“therewasnosignificantdifference.”Wesuggestthatthephraseusedbytheseauthors,“Wedeemedapvaluelessthan0.05tobesignificant,”shouldbestronglydiscouraged,ratherthanactivelydemandedasiscurrentlythecasebymanyjournaleditors.Totheircredit,theORBITAauthorsthemselveshaverecognizedthesecriticalissues(seehttps://twitter.com/ProfDFrancis/status/952008644018753536).

Inthecaseofstents,animportantdisconnectappearsbetweenthefindingsemphasizedintherecentstudy—howeverpresented—andthelargercontextoftreatmentsforheartdisease.Fromastatisticalperspective,thisappearstoreflectaproblemwiththeframingofclinicaltrialsasattemptstodiscoverwhetheratreatmenthasastatisticallysignificanteffect—commonlymisinterpretedtobeequivalenttoareal(non-zero)populationmeandifference.Powercalculationsareusedinanattempttoassurestableestimatesandagoodchanceoftheexperimentbeing“successful”,althoughwithintheseconstraintstherecanbeapushtowardconvenienceratherthanrelevanceofoutcomemeasures—whichisperhapsaninevitablecompromise.ORBITAshowsustheconfusionthatariseswhenatreatmentisreportedasasuccessorfailureinstatisticaltermsthataredivorcedfromclinicalcontext.

ORBITAwasnevermeanttobedefinitiveinabroadsense—itwasdesignedtofindastatisticallysignificantphysiologicaleffectofstentingonmeanexercisetime,withoutclarityontheclinicalrelevanceofanticipatedeffectsonthisoutcomemeasure.Indeed,alikelyreasonwhythestudywaslimitedinitssizeanddesignofthesesurrogateoutcomeswasbecausethisisallthatcouldhavepassedanethicalboardgiventhenoveltyoftheplaceboprocedureinthissetting.FurtherbackgroundonthesetopicsfromDarrelFrancis,theseniorauthoronthestudy,appearsatHarrell(2017b).Beyondimmediatenewsreports,onepositiveimpactofORBITAisthatbiggertrialsofstentingwithplaceboproceduresarenowmuchmorelikelywithamoredefinitivesetofmeasuredoutcomesthataremeaningfulforpatients.

Wedon’tseeanyeasyanswershere—long-termoutcomeswouldrequirealong-termstudy,afterall,andclinicaldecisionsneedtobemaderightaway,everyday—butperhapswecanuseourexaminationofthisparticularstudyanditsreportingtosuggestpracticaldirectionsforimprovementinhearttreatmentstudiesandinthedesignandreportingofclinicaltrialsmoregenerally.

References

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Table.Summarydatacomparingstentstoplacebo,fromTable3ofAl-Lameeetal.(2017).

Box1.Usingthereporteddatasummariestoobtaintheanalysiscontrollingforthepre-treatmentmeasureForeachofthetreatmentandcontrolgroups,wearegiventhestandarddeviationofthepre-testmeasurements,thestandarddeviationofthepost-testmeasurements,andthestandarddeviationoftheirdifference,whichcanbeobtainedbytakingthewidthoftheconfidenceintervalforthedifference,dividingby4togetthestandarderrorofthedifference,andthenmultiplyingby 𝑛togetbacktothestandarddeviation.

Thenweusetherule,sd(y! − y!) = sd y! ! + sd y! !

− 2ρ sd(y!)sd(y!)andsolveforρ,thecorrelationbetweenbeforeandaftermeasurementswithineachgroup.Theresultinthiscaseisρ=0.88withineachgroup.Wethenconvertthecorrelationtoaregressioncoefficientofy!ony!usingthewell-knownformula,β = ρ sd(y!)/sd(y!),whichyieldsβ = 0.88forthetreatedandβ = 0.86forthecontrolgroup.Ifthesetwocoefficientsweremuchdifferentfromeachother,wemightwanttoconsideraninteractionmodel(Gelman,2004),butheretheyarecloseenoughthatwesimplytaketheiraverage.

Weusetheaverage,β=0.87,in(2)andgetanestimatefortheadjustedmeandifferenceof21.3(indeed,quiteabithigherthanthereporteddifferenceingainscoresof16.6)withastandarderrorof12.5(veryslightlylowerthan12.7,thestandarderrorofthedifferenceingainscores)and95%CI−3.2to45.8s.Theestimateisnotquitetwostandarderrorsawayfromzero:thez-scoreis1.7,andthep-valueis0.09.

Box2.RecommendationsforAnalysesandReportingAnalyses1.Baselineadjustmentfordifferences:shouldbeprespecifiedfortheprimaryanalysiswherestrongconfounderssuchasabaselinemeasureoftheoutcomeareavailable.2.Beawareoffragilityofinferences.Fragilitycanbedemonstratedusingthesamplingorposteriordistributionasestimatedusingmathematicalmodeling,bootstrapsimulation,orBayesiananalysis.Reporting1.Avoiduseofsharpthresholdsforp-valuesandthuseliminatetheterm“statisticalsignificance”fromthereportingofresults.2.Considerthefullrange(upperandlowerends)ofintervalestimatesforimportantoutcomesandtheirpotentialinclusionofclinicallyimportantdifferences.3.Considerthepotentialforindividualvariabilityinresponses(heterogeneityoftreatmenteffects)andnotjustmeandifferences.