JournalofClinicalEpidemiology61(2008)344e349

ORIGINALARTICLES

TheStrengtheningtheReportingofObservationalStudiesinEpidemiology(STROBE)statement:guidelinesforreportingobservationalstudies

ErikvonElm

a

,

g

,DouglasG.Altman

c

,MatthiasEgger

a

,

b

,

*

,StuartJ.Pocock

d

,PeterC.G?tzsche

e

,JanP.Vandenbroucke

f

fortheSTROBEInitiative

aInstituteofSocialandPreventiveMedicine(ISPM),UniversityofBern,3012Bern,Switzerland

bDepartmentofSocialMedicine,UniversityofBristol,Bristol,UnitedKingdomcCentreforStatisticsinMedicine,UniversityofOxford,Oxford,UnitedKingdom

dLondonSchoolofHygieneandTropicalMedicine,UniversityofLondon,London,UnitedKingdom

eNordicCochraneCentre,Copenhagen,Denmark

fDepartmentofClinicalEpidemiology,LeidenUniversityHospital,Leiden,TheNetherlands

gDepartmentofMedicalBiometryandMedicalInformatics,UniversityMedicalCentre,Freiburg,Germany

Accepted18November2007

Abstract

Muchofbiomedicalresearchisobservational.Thereportingofsuchresearchisofteninadequate,whichhamperstheassessmentofitsstrengthsandweaknessesandofastudy’sgeneralizability.TheStrengtheningtheReportingofObservationalStudiesinEpidemiology(STROBE)Initiativedevelopedrecommendationsonwhatshouldbeincludedinanaccurateandcompletereportofanobservationalstudy.Wedefinedthescopeoftherecommendationstocoverthreemainstudydesigns:cohort,caseecontrol,andcross-sectionalstudies.Weconveneda2-dayworkshopinSeptember2004,withmethodologists,researchers,andjournaleditorstodraftachecklistofitems.Thislistwassubsequentlyrevisedduringseveralmeetingsofthecoordinatinggroupandine-maildiscussionswiththelargergroupofSTROBEcontributors,takingintoaccountempiricalevidenceandmethodologicalconsiderations.Theworkshopandthesubsequentiterativeprocessofconsultationandrevisionresultedinachecklistof22items(theSTROBEStatement)thatrelatetothetitle,abstract,introduction,methods,results,anddiscussionsectionsofarticles.Eighteenitemsarecommontoallthreestudydesignsandfourarespecificforcohort,caseecontrol,orcross-sectionalstudies.AdetailedExplanationandElaborationdocumentispublishedseparatelyandisfreelyavailableonthewebsitesofPLoSMedicine,AnnalsofInternalMedicine,andEpidemiology.WehopethattheSTROBEStatementwillcontributetoimprovingthequalityofreportingofobservationalstudies.2007Theauthors.PublishedbyElsevierInc.Allrightsreserved.

1.Introduction

Manyquestionsinmedicalresearchareinvestigatedinobservationalstudies

[1]

.Muchoftheresearchintothecauseofdiseasesreliesoncohort,caseecontrol,orcross-sectionalstudies.Observationalstudiesalsohavearoleinresearchintothebenefitsandharmsofmedicalinterven-tions

[2]

.Randomizedtrialscannotanswerallimportant

*Correspondingauthor.

E-mailaddress:

strobe@ispm.unibe.ch

(M.Egger).

InordertoencouragedisseminationoftheSTROBEStatement,thisar-ticleisfreelyaccessibleontheJournalofClinicalEpidemiologywebsite(

),andwillalsobepublishedinAnnalsofInternalMedicine,BMJ,BulletinoftheWorldHealthOrganization,Epidemiology,TheLancet,PLoSMedicine,andPreventiveMedicine.Theauthorsjointlyholdthecopyrightofthisarticle.Fordetailsonfurtheruse,seeSTROBEwebsite(

).

questionsaboutagivenintervention.Forexample,observa-tionalstudiesaremoresuitabletodetectrareorlateadverseeffectsoftreatmentsandaremorelikelytoprovideanindicationofwhatisachievedindailymedicalpractice

[3]

.

Researchshouldbereportedtransparentlysothatreaderscanfollowwhatwasplanned,whatwasdone,whatwasfound,andwhatconclusionsweredrawn.Thecredibil-ityofresearchdependsonacriticalassessmentbyothersofthestrengthsandweaknessesinstudydesign,conduct,andanalysis.Transparentreportingisalsoneededtojudgewhetherandhowresultscanbeincludedinsystematicreviews

[4,5]

.However,inpublishedobservationalresearchimportantinformationisoftenmissingorunclear.Ananal-ysisofepidemiologicalstudiespublishedingeneralmedi-calandspecialistjournalsfoundthattherationalebehindthechoiceofpotentialconfoundingvariableswasoften

0895-4356/08/$eseefrontmatter 2007Theauthors.PublishedbyElsevierInc.Allrightsreserved.

doi:10.1016/j.jclinepi.2007.11.008

E.vonElmetal./JournalofClinicalEpidemiology61(2008)344e349

345

notreported

[6]

.Onlyfewreportsofcaseecontrolstudiesinpsychiatryexplainedthemethodsusedtoidentifycasesandcontrols

[7]

.Inasurveyoflongitudinalstudiesinstrokeresearch,17of49articles(35%)didnotspecifytheeligibilitycriteria

[8]

.Othershavearguedthatwithoutsufficientclarityofreporting,thebenefitsofresearchmightbeachievedmoreslowly

[9]

,andthatthereisaneedforguidanceinreportingobservationalstudies

[10,11]

.

Recommendationsonthereportingofresearchcanim-provereportingquality.TheConsolidatedStandardsofReportingTrials(CONSORT)Statementwasdevelopedin1996andrevised5yearslater

[12]

.Manymedicaljour-nalssupportedthisinitiative

[13]

,whichhashelpedtoim-provethequalityofreportsofrandomizedtrials

[14,15]

.Similarinitiativeshavefollowedforotherresearchareasde.g.,forthereportingofmeta-analysesofrandomizedtrials

ordiagnosticstudies

[17]

.Weestablishedanetworkofmethodologists,researchers,andjournaleditorstodeveloprecommendationsforthereportingofobservationalresearch:theStrengtheningtheReportingofObservationalStudiesinEpidemiology(STROBE)Statement.

1.1.AimsanduseoftheSTROBEStatement

TheSTROBEStatementisachecklistofitemsthatshouldbeaddressedinarticlesreportingonthethreemainstudyde-signsofanalyticalepidemiology:cohort,caseecontrol,andcross-sectionalstudies.Theintentionissolelytoprovideguidanceonhowtoreportobservationalresearchwell:theserecommendationsarenotprescriptionsfordesigningorcon-ductingstudies.Also,whileclarityofreportingisaprerequi-sitetoevaluation,thechecklistisnotaninstrumenttoevaluatethequalityofobservationalresearch.

Here,wepresenttheSTROBEStatementandexplainhowitwasdeveloped.Inadetailedcompanionpaper,theExplanationandElaborationarticle

[18e20]

,wejustifytheinclusionofthedifferentchecklistitemsandgivemeth-odologicalbackgroundandpublishedexamplesofwhatweconsidertransparentreporting.WestronglyrecommendusingtheSTROBEchecklistinconjunctionwiththeexplanatoryarticle,whichisavailablefreelyonthewebsitesofPLoSMedicine(

/

),AnnalsofInternalMedicine(

/

),andEpidemiology(

/

).

1.2.DevelopmentoftheSTROBEStatement

WeestablishedtheSTROBEInitiativein2004,obtainedfundingforaworkshopandsetupawebsite(

http://

/

).Wesearchedtextbooks,bib-liographicdatabases,referencelists,andpersonalfilesforrelevantmaterial,includingpreviousrecommendations,empiricalstudiesofreportingandarticlesdescribingrele-vantmethodologicalresearch.Becauseobservationalre-searchmakesuseofmanydifferentstudydesigns,wefeltthatthescopeofSTROBEhadtobeclearlydefinedearly

on.Wedecidedtofocusonthethreestudydesignsthatareusedmostwidelyinanalyticalobservationalresearch:cohort,caseecontrol,andcross-sectionalstudies.

Weorganizeda2-dayworkshopinBristol,UK,inSeptember2004.Twenty-threeindividualsattendedthismeeting,includingeditorialstafffromAnnalsofInternalMedicine,BMJ,BulletinoftheWorldHealthOrganization,InternationalJournalofEpidemiology,JAMA,PreventiveMedicine,andTheLancet,aswellasepidemiologists,meth-odologists,statisticians,andpractitionersfromEuropeandNorthAmerica.Writtencontributionsweresoughtfrom10otherindividualswhodeclaredaninterestincontributingtoSTROBE,butcouldnotattend.Threeworkinggroupsidentifieditemsdeemedtobeimportanttoincludeincheck-listsforeachtypeofstudy.Aprovisionallistofitemspre-paredinadvance(availablefromourwebsite)wasusedtofacilitatediscussions.Thethreedraftchecklistswerethendiscussedbyallparticipantsand,wherepossible,itemswererevisedtomakethemapplicabletoallthreestudydesigns.Inafinalplenarysession,thegroupdecidedonthestrategyforfinalizinganddisseminatingtheSTROBEStatement.

Aftertheworkshop,wedraftedacombinedchecklistin-cludingallthreedesignsandmadeitavailableonourwebsite.Weinvitedparticipantsandadditionalscientistsandeditorstocommentonthisdraftchecklist.Wesubsequentlypublishedthreerevisionsonthewebsiteandtwosumma-riesofcommentsreceivedandchangesmade.Duringthisprocessthecoordinatinggroup(i.e.,theauthorsofthepres-entpaper)metoneightoccasionsfor1or2daysandheldseveraltelephoneconferencestorevisethechecklistandtopreparethepresentpaperandtheExplanationandElabora-tionpaper

[18e20]

.ThecoordinatinggroupinvitedthreeadditionalcoauthorswithmethodologicalandeditorialexpertisetohelpwritetheExplanationandElaborationpaper,andsoughtfeedbackfrommorethan30people,whoarelistedattheendofthispaper.Weallowedseveralweeksforcommentsonsubsequentdraftsofthepaperandremindedcollaboratorsaboutdeadlinesbye-mail.

1.3.STROBEcomponents

TheSTROBEStatementisachecklistof22itemsthatweconsideressentialforgoodreportingofobservationalstudies(

Table1

).Theseitemsrelatetothearticle’stitleandabstract(item1),theintroduction(items2and3),methods(items4e12),results(items13e17)anddiscus-sionsections(items18e21),andotherinformation(item22onfunding).Eighteenitemsarecommontoallthreedesigns,whereasfour(items6,12,14,and15)aredesignspecific,withdifferentversionsforallorpartoftheitem.Forsomeitems(indicatedbyasterisks),informationshouldbegivenseparatelyforcasesandcontrolsincaseecontrolstudies,orexposedandunexposedgroupsincohortandcross-sectionalstudies.Althoughpresentedhereasasinglechecklist,separatechecklistsareavailableforeachofthethreestudydesignsontheSTROBEwebsite.

346 E.vonElmetal./JournalofClinicalEpidemiology61(2008)344e349

Table1

TheSTROBEstatementdchecklistofitemsthatshouldbeaddressedinreportsofobservationalstudies

Itemnumber

Recommendation

Titleandabstract

1

(a)Indicatethestudy’sdesignwithacommonlyusedterminthetitleortheabstract

(b)Provideintheabstract,aninformativeandbalancedsummaryofwhatwasdoneandwhat

wasfound

Introduction

Background/rationale

2

Explainthescientificbackgroundandrationalefortheinvestigationbeingreported

Objectives

3

Statespecificobjectives,includinganyprespecifiedhypotheses

Methods

Studydesign

4

Presentkeyelementsofstudydesignearlyinthepaper

Setting

5

Describethesetting,locations,andrelevantdates,includingperiodsofrecruitment,exposure,follow

up,anddatacollection

Participants

6

(a)CohortstudydGivetheeligibilitycriteria,andthesourcesandmethodsofselectionof

participants.Describemethodsoffollowup

Case-controlstudydGivetheeligibilitycriteria,andthesourcesandmethodsofcaseascertainment

andcontrolselection.Givetherationaleforthechoiceofcasesandcontrols

Cross-sectionalstudydGivetheeligibilitycriteria,andthesourcesandmethodsofselection

ofparticipants

(b)CohortstudydFormatchedstudies,givematchingcriteriaandnumberofexposedandunexposed

Case-controlstudydFormatchedstudies,givematchingcriteriaandthenumberofcontrols

percase

Variables

7

Clearlydefinealloutcomes,exposures,predictors,potentialconfounders,andeffectmodifiers.

Givediagnosticcriteria,ifapplicable

Datasources/measurement

8

*

Foreachvariableofinterest,givesourcesofdataanddetailsofmethodsofassessment

(measurement).Describecomparabilityofassessmentmethodsifthereismorethanonegroup

Bias

9

Describeanyeffortstoaddresspotentialsourcesofbias

Studysize

10

Explainhowthestudysizewasarrivedat

Quantitativevariables

11

Explainhowquantitativevariableswerehandledintheanalyses.Ifapplicable,describewhich

groupingswerechosen,andwhy

Statisticalmethods

12

(a)Describeallstatisticalmethods,includingthoseusedtocontrolforconfounding

(b)Describeanymethodsusedtoexaminesubgroupsandinteractions

(c)Explainhowmissingdatawereaddressed

(d)CohortstudydIfapplicable,explainhowlosstofollowupwasaddressed

Case-controlstudydIfapplicable,explainhowmatchingofcasesandcontrolswasaddressed

Cross-sectionalstudydIfapplicable,describeanalyticalmethodstakingaccountofsampling

strategy

(e)Describeanysensitivityanalyses

Results

Participants

13

*

(a)Reportthenumbersofindividualsateachstageofthestudyde.g.,numberspotentiallyeligible,

examinedforeligibility,confirmedeligible,includedinthestudy,completingfollowup,

andanalyzed

(b)Givereasonsfornonparticipationateachstage

(c)Consideruseofaflowdiagram

Descriptivedata

14

*

(a)Givecharacteristicsofstudyparticipants(e.g.,demographic,clinical,social)andinformation

onexposuresandpotentialconfounders

(b)Indicatethenumberofparticipantswithmissingdataforeachvariableofinterest

(c)CohortstudydSummarizefollow-uptime(e.g.,averageandtotalamount)

Outcomedata

15

*

CohortstudydReportnumbersofoutcomeeventsorsummarymeasuresovertime

Case-controlstudydReportnumbersineachexposurecategory,orsummarymeasuresofexposure

Cross-sectionalstudydReportnumbersofoutcomeeventsorsummarymeasures

Mainresults

16

(a)Giveunadjustedestimatesand,ifapplicable,confounder-adjustedestimatesandtheirprecision

(e.g.,95%confidenceinterval).Makeclearwhichconfounderswereadjustedforandwhythey

wereincluded

(b)Reportcategoryboundarieswhencontinuousvariableswerecategorized

(c)Ifrelevant,considertranslatingestimatesofrelativeriskintoabsoluteriskforameaningful

timeperiod

Otheranalyses

17

Reportotheranalysesdonede.g.,analysesofsubgroupsandinteractions,andsensitivityanalyses

Discussion

Keyresults

18

Summarizekeyresultswithreferencetostudyobjectives

Limitations

19

Discusslimitationsofthestudy,takingintoaccountsourcesofpotentialbiasorimprecision.

Discussbothdirectionandmagnitudeofanypotentialbias

(Continued)

E.vonElmetal./JournalofClinicalEpidemiology61(2008)344e349

347

Table1

Continued

Itemnumber

Recommendation

Interpretation

20

Giveacautiousoverallinterpretationofresultsconsideringobjectives,limitations,multiplicityof

analyses,resultsfromsimilarstudies,andotherrelevantevidence

Generalizability

21

Discussthegeneralizability(externalvalidity)ofthestudyresults

Otherinformation

Funding

22

Givethesourceoffundingandtheroleofthefundersforthepresentstudyand,ifapplicable,forthe

originalstudyonwhichthepresentarticleisbased

Givesuchinformationseparatelyforcasesandcontrolsincase-controlstudies,and,ifapplicable,forexposedandunexposedgroupsincohortandcross-sectionalstudies.

Note:AnExplanationandElaborationarticlediscusseseachchecklistitemandgivesmethodologicalbackgroundandpublishedexamplesoftransparentreporting.TheSTROBEchecklistisbestusedinconjunctionwiththisarticle(freelyavailableonthewebsitesofPLoSMedicineat

http://www.plosmedi

,AnnalsofInternalMedicineat

,andEpidemiologyat

).Separateversionsofthechecklistforcohort,case-control,andcross-sectionalstudiesareavailableontheSTROBEwebsiteat

.

1.4.Implicationsandlimitations

TheSTROBEStatementwasdevelopedtoassistauthorswhenwritingupanalyticalobservationalstudies,tosupporteditorsandreviewerswhenconsideringsucharticlesforpublication,andtohelpreaderswhencriticallyappraisingpublishedarticles.Wedevelopedthechecklistthroughanopenprocess,takingintoaccounttheexperiencegainedwithpreviousinitiatives,inparticularCONSORT.Wereviewedtherelevantempiricalevidenceaswellasmeth-odologicalworkandsubjectedconsecutivedraftstoanextensiveiterativeprocessofconsultation.Thechecklistpresentedhereisthusbasedoninputfromalargenumberofindividualswithdiversebackgroundsandperspectives.Thecomprehensiveexplanatoryarticle

[18e20]

,whichisintendedforusealongsidethechecklist,alsobenefitedgreatlyfromthisconsultationprocess.

Observationalstudiesserveawiderangeofpurposes,onacontinuumfromthediscoveryofnewfindingstothecon-firmationorrefutationofpreviousfindings

[18e20]

.Somestudiesareessentiallyexploratoryandraiseinterestinghypotheses.Otherspursueclearlydefinedhypothesesinavailabledata.Inyetanothertypeofstudies,thecollectionofnewdataisplannedcarefullyonthebasisofanexistinghypothesis.Webelievethepresentchecklistcanbeusefulforallthesestudies,sincethereadersalwaysneedtoknowwhatwasplanned(andwhatwasnot),whatwasdone,whatwasfound,andwhattheresultsmean.WeacknowledgethatSTROBEiscurrentlylimitedtothreemainobserva-tionalstudydesigns.Wewouldwelcomeextensionsthatadaptthechecklisttootherdesignsde.g.,case-crossoverstudiesorecologicalstudiesdandalsotospecifictopicareas.FourextensionsarenowavailablefortheCONSORTstatement

[21e24]

.AfirstextensiontoSTROBEisunder-wayforgeneediseaseassociationstudies:theSTROBEExtensiontoGeneticAssociationstudies(STREGA)initia-tive

[25]

.WeaskthosewhoaimtodevelopextensionsoftheSTROBEStatementtocontactthecoordinatinggroupfirsttoavoidduplicationofeffort.

TheSTROBEStatementshouldnotbeinterpretedasanattempttoprescribethereportingofobservationalresearch

inarigidformat.Thechecklistitemsshouldbeaddressedinsufficientdetailandwithclaritysomewhereinanarticle,buttheorderandformatforpresentinginformationdependsonauthorpreferences,journalstyle,andthetradi-tionsoftheresearchfield.Forinstance,wediscussthere-portingofresultsunderanumberofseparateitems,whilerecognizingthatauthorsmightaddressseveralitemswithinasinglesectionoftextorinatable.Also,item22,onthesourceoffundingandtheroleoffunders,couldbead-dressedinanappendixorinthemethodssectionofthear-ticle.Wedonotaimatstandardizingreporting.Authorsofrandomizedclinicaltrialswereaskedbyaneditorofaspe-cialistmedicaljournalto‘‘CONSORT’’theirmanuscriptsonsubmission

[26]

.Webelievethatmanuscriptsshouldnotbe‘‘STROBEd,’’inthesenseofregulatingstyleorter-minology.Weencourageauthorstousenarrativeelements,includingthedescriptionofillustrativecases,tocomple-menttheessentialinformationabouttheirstudy,andtomaketheirarticlesaninterestingread

[27]

.

WeemphasizethattheSTROBEStatementwasnotde-velopedasatoolforassessingthequalityofpublishedob-servationalresearch.Suchinstrumentshavebeendevelopedbyothergroupsandwerethesubjectofarecentsystematicreview

[28]

.IntheExplanationandElaborationpaper,weusedseveralexamplesofgoodreportingfromstudieswhoseresultswerenotconfirmedinfurtherresearchdtheimportantfeaturewasthegoodreporting,notwhethertheresearchwasofgoodquality.However,ifSTROBEisadoptedbyauthorsandjournals,issuessuchasconfound-ing,bias,andgeneralizabilitycouldbecomemoretranspar-ent,whichmighthelptempertheoverenthusiasticreportingofnewfindingsinthescientificcommunityandpopularmedia

[29]

,andimprovethemethodologyofstudiesinthelongterm.Betterreportingmayalsohelptohavemoreinformeddecisionsaboutwhennewstudiesareneeded,andwhattheyshouldaddress.

Wedidnotundertakeacomprehensivesystematicreviewforeachofthechecklistitemsandsubitems,ordoourownresearchtofillgapsintheevidencebase.Further,althoughnoonewasexcludedfromtheprocess,the

348 E.vonElmetal./JournalofClinicalEpidemiology61(2008)344e349

compositionofthegroupofcontributorswasinfluencedbyexistingnetworksandwasnotrepresentativeintermsofge-ography(itwasdominatedbycontributorsfromEuropeandNorthAmerica)andprobablywasnotrepresentativeintermsofresearchinterestsanddisciplines.WestressthatSTROBEandotherrecommendationsonthereportingofresearchshouldbeseenasevolvingdocumentsthatrequirecontinualassessment,refinement,and,ifnecessary,change.WewelcomesuggestionsforthefurtherdisseminationofSTROBEde.g.,byrepublicationofthepresentarticleinspecialistjournalsandinjournalspublishedinotherlanguages.Groupsorindividualswhointendtotranslatethechecklisttootherlanguagesshouldconsultthecoordi-natinggroupbeforehand.Wewillrevisethechecklistinthefuture,takingintoaccountcomments,criticism,newevidence,andexperiencefromitsuse.WeinvitereaderstosubmittheircommentsviatheSTROBEwebsite(

/

).

Acknowledgments

WearegratefultoGerdAntes,KayDickersin,ShahEbrahim,andRichardLilfordforsupportingtheSTROBEInitiative.Wearegratefultothefollowinginstitutionsthathavehostedworkingmeetingsofthecoordinatinggroup:InstituteofSocialandPreventiveMedicine(ISPM),UniversityofBern,Bern,Switzerland;DepartmentofSo-cialMedicine,UniversityofBristol,Bristol,UK;LondonSchoolofHygieneandTropicalMedicine,London,UK;NordicCochraneCentre,Copenhagen,Denmark;andCentreforStatisticsinMedicine,Oxford,UK.Wearegratefultosixreviewerswhoprovidedhelpfulcommentsonapreviousdraftofthispaper.

ThefollowingindividualshavecontributedtothecontentandelaborationoftheSTROBEStatement:Doug-lasGAltman,MariaBlettner,PaoloBoffetta,HermannBrenner,Genevie`veChe?ne,CyrusCooper,GeorgeDavey-Smith,ErikvonElm,MatthiasEgger,FranceGagnon,PeterCG?tzsche,PhilipGreenland,SanderGreenland,ClaireInfante-Rivard,JohnIoannidis,AstridJames,GiselleJones,BrunoLedergerber,JulianLittle,MargaretMay,DavidMoher,HoomanMomen,AlfredoMorabia,HalMorgenstern,CynthiaDMulrow,FredPaccaud,StuartJPocock,CharlesPoole,DrummondRennie,MartinRo¨o¨sli,DietrichRothenbacher,KennethRothman,CarolineSabin,WilliSauerbrei,LaleSay,JamesJSchlesselman,JonathanSterne,HollySyddall,JanPVandenbroucke,IanWhite,SusanWieland,HywelWilliams,GuangYongZou.

TheworkshopwasfundedbytheEuropeanScienceFoundation(ESF).AdditionalfundingwasreceivedfromtheMedicalResearchCouncilHealthServicesResearchCollaborationandtheNationalHealthServicesResearchandDevelopmentMethodologyProgramme.ThefundershadnoroleintheelaborationoftheSTROBEStatement,decisiontopublishit,orpreparationofthemanuscript.

Theauthorshavedeclaredthatnocompetinginterestsexist.

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