OriginalPaper

DebbieRankin1PhD,Correspondingauthor,

d.rankin1@ulster.ac.uk

,+442871675841

MichaelaBlack1PhD,

mm.black@ulster.ac.uk

RaymondBond2PhD,

rb.bond@ulster.ac.uk

JonathanWallace2MSc,

jg.wallace@ulster.ac.uk

MauriceMulvenna2PhD,

md.mulvenna@ulster.ac.uk

GorkaEpelde3,4PhD,

gepelde@

1SchoolofComputing,EngineeringandIntelligentSystems,UlsterUniversity,Derry~Londonderry,NorthernIreland,UnitedKingdom

2SchoolofComputing,UlsterUniversity,Jordanstown,NorthernIreland,UnitedKingdom

3VicomtechFoundation,BasqueResearchandTechnologyAlliance(BRTA),Donostia-SanSebastián,Spain

4BiodonostiaHealthResearchInstitute,eHealthGroup,Donostia-SanSebastián,Spain

ReliabilityofSupervisedMachineLearningUsingSyntheticDatainHealthcare:AModeltoPreservePrivacyforDataSharing

Abstract

Background:

Theexploitationofsyntheticdatainhealthcareisatanearlystage.Syntheticdatagenerationcouldunlockthevastpotentialwithinhealthcaredatasetsthataretoosensitiveforreleaseduetoprivacyconcerns.Severalsyntheticdatageneratorshavebeendevelopedtodate,howeverstudiesevaluatingtheirefficacyandgeneralisabilityarescarce.

Objective:

Thisworksetsouttounderstandthedifferenceinperformanceofsupervisedmachinelearningmodelstrainedonsyntheticdatacomparedwiththosetrainedonrealdata.

Methods:

Atotalof19openhealthcaredatasetscontainingbothcategoricalandnumericaldatahavebeenselectedforexperimentalwork.SyntheticdataisgeneratedusingthreepopularsyntheticdatageneratorsthatapplyClassificationandRegressionTrees,parametricandBayesiannetworkapproaches.Realandsyntheticdataareused(separately)totrainfivesupervisedmachinelearningmodels:stochasticgradientdescent,decisiontree,k-nearestneighbors,randomforestandsupportvectormachine.Modelsaretestedonlyonrealdatatodeterminewhetheramodeldevelopedbytrainingonsyntheticdatacanbeputintousebyhealthcaredepartmentsandusedtoaccuratelyclassifynew,realexamples.Evaluationmetricsarecomputedanddifferentialsinthesescoresarecompared.Theimpactofstatisticaldisclosurecontrolonmodelperformanceisalsoassessed.

Results:

TheaccuracyofMLmodelstrainedonsyntheticdataislowerthanmodelstrainedonrealdatain92%ofcases.Tree-basedmodelstrainedonsyntheticdatahavedeviationsinaccuracyfrommodelstrainedonrealdataof17.7-19.3%,whilstothermodelshavelowerdeviationsof5.8-7.2%.Thewinningclassifierwhentrainedandtestedonrealdataversusmodelstrainedonsyntheticdataandtestedonrealdataisthesamein26.3%ofcasesforCARTandparametricsyntheticdata,andin21.1%ofcasesforBayesiannetworkgeneratedsyntheticdata.Tree-basedmodelsperformbestwithrealdataandarethewinningclassifierin94.7%ofcases.Thisisnotthecaseformodelstrainedonsyntheticdata.Whentree-basedmodelsarenotconsidered,thewinningclassifierforrealandsyntheticdataismatchedin73.7%,52.6%and68.4%ofcasesforCART,parametricandBayesiannetworksyntheticdata,respectively.Statisticaldisclosurecontrolmethodsdidnothaveanotableimpactondatautility.

Conclusions:

Theresultsofthisstudyarepromisingwithsmalldecreasesinaccuracyobservedinmodelstrainedwithsyntheticdatacomparedtomodelstrainedwithrealdata,wherebotharetestedonrealdata.Suchdeviationsareexpectedandmanageable.Tree-basedclassifiershavesomesensitivitytosyntheticdataandtheunderlyingcauserequiresfurtherinvestigation.Thisstudyhighlightsthepotentialofsyntheticdataandtheneedforfurtherevaluationitsrobustness.Syntheticdatamustensureindividualprivacyanddatautilityispreservedinordertoinstilconfidenceinhealthcaredepartmentswhenutilisingsuchdatatoinformpolicydecision-making.

Keywords:SyntheticData;SupervisedMachineLearning;DataUtility;Healthcare;DecisionSupport;StatisticalDisclosureControl

Introduction

Background

NationalHealthcareDepartmentsholdvastvolumesofdataonpatientsandthepopulationthatisnotbeingusedtoitsfullpotentialduetovalidprivacyconcerns.Machinelearning(ML)hasthepotentialtovastlyimprovedecisionsandoutcomesinhealthcareandyettheseimprovementshavenotyetbeenfullyrealised.Thereasonmaybeinpartrelatedtoanissuethatfacesmanydatascientistsandresearchersinthearea:thelimitedavailabilityoforaccesstodata,orthereadinessforhealthcareinstitutionstosharedata.Privacyconcernsoverpersonaldata,andinparticularhealthcaredata,meansthatalthoughthedataexists,itisdeemedtoosensitiveforpublicrelease[1],eveninthecaseofseriousresearch.

Onewaytoovercometheissueofdataavailabilityistousefullysyntheticdataasanalternativetorealdata.Theexploitationofsyntheticdatainhealthcareisatanearlystageandisgainingincreasingattention.Syntheticdataisdatathatissimulatedfromrealdatabyusingtheunderlyingstatisticalpropertiesoftherealdatatoproducesyntheticdatasetsthatexhibitthesesamestatisticalproperties.Syntheticdatacanrepresentthepopulationintheoriginaldatawhilstavoidinganydivulgenceofreal,potentiallypersonal,confidentialandsensitivedata.Inthecaseofhealth-relateddata,thiswouldensurethatactualpatientrecordsarenotdisclosedthusavoidinggovernanceandconfidentialityissues.Therearethreetypesofsyntheticdata:fullysynthetic,partiallysynthetic,andhybridsynthetic.Thisworkconsidersfullysyntheticdatawhichdoesnotcontainoriginaldata.

Syntheticdatacanbeusedintwoways:toaugmentanexistingdatasetthusincreasingitssize,fortimeswhenadatasetisunbalancedduetothelimitedoccurrenceofaneventorwhenmoreexamplesarerequired[2,3];andtogenerateafullysyntheticdatasetthatisrepresentativeoftheoriginaldataset,fortimeswhendataisnotavailableduetoitssensitivenature[4].Thelatterisconsideredinthisworkasakeyrequirementforhealthcaredatasharing.

Traditionally,dataperturbationtechniquessuchasdataswapping,datamasking,cellsuppressionandaddingnoise,havebeenappliedtorealdatatomodifyandthusprotectthedatafromdisclosurepriortoreleasingit.However,suchmethodsdonoteliminatedisclosureriskandcanimpacttheutilityofthedata,particularlyifmultivariaterelationshipsarenotconsidered[5].SyntheticdatawasfirstproposedbyRubin[6]andLittle[7].Raghunathan,ReiterandRubin[8]implementedandextendeduponthis,pioneeringthemultipleimputationapproachtosyntheticdatageneration,exemplifiedinarangeofstudies[9-14].Reiter[15]thenintroducedanalternativemethodofsynthesisingdatathroughanon-parametrictree-basedtechniquethatutilisesClassificationandRegressionTrees(CART).AmorerecenttechniqueproposesaBayesiannetworkapproachforsyntheticdatageneration[16].Syntheticdataisconsideredasecureapproachforenablingpublicreleaseofsensitivedataasitgoesbeyondtraditionalde-identificationmethodsbygeneratingafakedatasetthatdoesnotcontainanyoftheoriginal,identifiableinformationfromwhichitwasgenerated,whilstretainingthevalidstatisticalpropertiesoftherealdata.Therefore,theriskofdisclosureofarealpersonorreverseengineeringisconsideredtobeunlikely[17].

Whilstanumberofsyntheticdatageneratorshavebeendeveloped,empiricalevidenceoftheirefficacyhasnotbeenfullyexplored.Thisworkextendsapreliminarystudy[18]andinvestigateswhetherfullysyntheticdatacanpreservethehiddencomplexpatternsthatsupervisedMLcanuncoverfromrealdata,andthereforewhetheritcanbeusedasavalidalternativetorealdatawhendevelopingeHealthapplicationsandhealthcarepolicymakingsolutions.Thiswillbeachievedbyexperimentingwitharangeofopenhealthcaredatasets.Syntheticdatawillbegeneratedusingthreewellknownsyntheticdatagenerationtechniques.SupervisedMLalgorithmswillbeusedtovalidatetheperformanceofthesyntheticdatasets.Statisticaldisclosurecontrol(SDC)methodsthatcanfurtherdecreasethedisclosureriskassociatedwithsyntheticdatawillalsobeconsidered.

Overview

Toinformtheviabilityoftheuseofsyntheticdataasavalidandreliablealternativetorealdatainthehealthcaredomainwewillanswerthefollowingresearchquestions:

WhatisthedifferentialinperformancewhenusingsyntheticdataversusrealdatafortrainingandtestingsupervisedMLmodels?

WhatisthevarianceofabsolutedifferenceofaccuraciesbetweenMLmodelstrainingonrealandsyntheticdatasets?

HowoftendoesthewinningMLtechniquechangewhentrainingusingrealdatatotrainingusingsyntheticdata?

Whatistheimpactofstatisticaldisclosurecontrol(i.e.privacyprotection)measuresontheutilityofsyntheticdata(i.e.similaritytorealdata)?

Toanswerthesequestions,19openhealthcaredatasetscontainingbothcategoricalandnumericaldatahavebeenselectedforexperimentation[19].Syntheticdatasetsaregeneratedforeachofthese19datasetsusingthreepopularsyntheticdatageneratorsthatapplyCART[15,17],parametric[8,17]andBayesiannetwork[16]approaches,respectively,toenablearobustcomparisonofthethreesyntheticdatagenerationtechniquesacrossabroadrangeofdata.

Initiallyweanalysewhetherthemultivariaterelationshipsthatexistintherealdataarepreservedinthesyntheticversionsofthedata,fordatageneratedusingeachofthethreesyntheticdatagenerationtechniques,bycomputingpairwisemutualinformationscoresforeachvariablepaircombinationineachdataset[16].Itisimportantthatsuchrelationshipsareretainedwhendataissynthesised.

ToevaluatetheutilityofsyntheticdataforMachineLearning,wetheninvestigatetheperformanceofsupervisedMLmodelstrainedonsyntheticdataandtestedonrealdata,comparedwithmodelstrainedonrealdataandalsotestedontherealdata.Thisallowsustodetermineifamodeldevelopedusingsyntheticdatacanclassifyrealdataexamplesasaccuratelyandreliablyasamodeldevelopedusingrealdata.Weconsiderfivedifferentsupervisedmachinelearningmodelstocompareperformanceanddetermineiftherearedifferencesinrobustnessacrosseachofthesemodels.Standardevaluationmetricsarecomputedformodelstrainedonrealandsyntheticdata,foreachMLmodel,andforeachdataset[20].Thedifferencesinaccuracyformodelstrainedonsyntheticdataversusmodelstrainedonrealdataarecomputedtoanalysetheextenttowhichsyntheticdatacausesadegradationinmodelperformance,ifany.

ItispertinentthattheoptimalMLmodelbuiltusingsyntheticdatamatchestheoptimalMLmodelthatwouldbeselectedifrealdatawereusedinthemodeltrainingprocess.Thiswouldprovidestakeholdersinhealthcarewithconfidenceintheuseofsyntheticdataformodeldevelopment.Thus,weconsiderhowoftenthebestMLclassifierbuiltusingsyntheticdatamatchesthebestMLmodelbuiltusingrealdata.

Finally,theimpactofanumberofstatisticaldisclosurecontrolmethodsonmodelperformanceisassessed.Statisticaldisclosurecontrolmethodsseektofurtherenhancedataprivacy;however,thiscanleadtoalossinusefulnessofthedata[21]andweconsidertheextenttowhichperformancedegradationoccursasaresultofSDC.

Thislarge-scaleassessmentofthereliabilityofsyntheticdatawhenusedforsupervisedML,utilising19healthcaredatasetsand3syntheticdatagenerationtechniques,providesanimportantcontributioninrelationtothetrustandconfidencethatstakeholdersinhealthcarecanhaveinsyntheticdata.Wealsoproposeapipelinetoillustratehowsyntheticdatacanpotentiallyfitwithinthehealthcareprovidercontext.Thisworkdemonstratesthepromisingperformanceofsyntheticdatawhilsthighlightingitslimitationsandfutureworkdirectionstoovercomethem.

SyntheticData:PresentandFutureUse

ThevalidityanddisclosureriskassociatedwithsyntheticdatahasbeenunderinvestigationbytheU.S.CensusBureausince2003forthepurposeofcreatingpublicusedatafromacombinationofsensitivedatafromtheCensusBureau’sSurveyofIncomeandProgramParticipation(SIPP),theInternalRevenueService’s(IRS)individuallifetimeearningsdata,andtheSocialSecurityAdministration’s(SSA)individualbenefitdata[22,23].Thegoalwastoenablethereleaseofsynthesisedperson-levelrecordscontainingpersonalandfinancialcharacteristicsfromconfidentialdatasets,whilstpreservingprivacy.Successfulresultshaveledtothereleaseofpublicusesyntheticdatafiles.ResearcherscanhavetheirworkvalidatedagainsttheGoldStandard(real)databytheCensusBureau,thusenablingthemtodeterminetheimpactofsyntheticdataontheirexploratoryanalysesandmodeldevelopmentandhaveconfidenceintheirresults,whilstalsoallowingtheCensusBureautocontinuouslyimprovetheirsynthesistechniques.Thepublicreleaseofthisdatahasprovidedsignificantbenefittotheresearchcommunityandgeneralpopulation,enablingmoreextensiveeconomicpolicyresearchtobeperformedbygroupswhocouldnotpreviouslyaccessusefuldata[24-29].ThisworkledtothereleaseoffurthersyntheticdatasetsbytheCensusBureau.TheSyntheticLongitudinalBusinessDatabase(SynLBD)comprisesdatafromanannualeconomiccensusofestablishmentsintheU.S.[30].Thisdatasetprovidesbroadaccesstorichdatathatsupportstheresearchandpolicy-makingcommunitiesinbusinessandemploymentrelatedtopics.OnTheMapisatoolutilisingsyntheticdatatoprovideworkforcerelatedmaps,demographicprofilesandreportsofU.S.citizens,aswellasdisastereventinformationandtheimpactofsucheventsonworkersandemployers[31].Similarly,syntheticdatahasalsobeenunderinvestigationintheUKasameanstoprovidepublicaccesstorichdatafromUKLongitudinalStudies[32-34]thatcontainhighlysensitivedatalinkingnationalcensusdatatoadministrativedataforindividualsandtheirfamilies.

Thesedatasetsenableresearcherstoexploredataanddevelopandtestcodeandmodelsoutsidethesecureenvironmentwhererealdataresideswithnorestrictions,whilstthedataownersprovideavalidationmechanismwhereresults,codeandmodelscanbevalidatedonbehalfofresearchersontherealdatawithinthesecureenvironmentandfeedbackprovided.Thisprocessincreasesresearchproductivitywhilstensuringthedevelopmentofrobustandvalidmodels[35].

Whilstsyntheticdatahasbeenusedtoaccelerateanddemocratisebusinessandeconomicpolicyresearch[22-35],itisnotcurrentlyinuseforhealthcareresearch,anareathatcouldbenefitenormously.Withadvancementsintechnology,particularlyMLandartificialintelligence(AI),thepotentialtodevelopdiagnostictoolsforcliniciansanddatadrivendecision-makingplatformsforhealthpolicy-makersisever-increasing[36,37].Suchtoolsrequireaccesstohealthcaredata,forexample,totrainAIalgorithmsandproducemodelsthatcanidentifyhealthconditionsandhealth-relatedpatternsacrossthepopulation.Currentlyitcantakealengthyperiodoftimeforresearcherstogainaccesstohealthcaredata,arichandunder-utilisedresource,duetoprivacyconcerns[38-42].Forexample,inthecaseofthe40monthMIDASProject[36,43]developingadata-drivendecisionmakingtoolforhealthcarepolicymakers,ittookmorethan20monthstoobtainaccesstotherequireddataduetolegalandethicalconstraints.Inaddition,anumberofimportantdatavariablescouldnotmadeavailablewhichrestrictedtheutilityoftheplatformunderdevelopment.Withthehelpofsyntheticdata,suchdata,withmoreorallvariablesincluded,couldhavebeenmadeavailableinamatterofweeksthusprovidingmoretimefordevelopmentandevaluationoftheplatform.Theplatformcouldthenhavebeeninstalledinhealthcaresitesmorequicklyandconnectedtorealdataforvalidationandcomparisonofperformanceforsyntheticversusrealdata,enablingperformancetweakstomitigatebiasintroducedbysyntheticdata,ifany.Syntheticdatacouldalsoenablecross-siteanalyticsacrossvarioushealthregions,thatwouldenablepolicymakerstoconnecttheirhealthspacesandpotentiallyprovidesignificantenhancementstocross-nationalhealthpolicy.

Theultimategoalofthisworkistofurtherassessthevalidityanddisclosureriskofsyntheticdataunderthestringentconditionsassociatedwithhealthcaredata,withtheviewtosuccessfullydevelopingapipelineforuseinhealthcarethatenablessyntheticdatasetstobereleasedpubliclytoresearcherswhowouldotherwisenotbeabletoaccessthedata,oraccessitinatimelyfashion,inordertoaccelerateresearchbyenablingthewiderresearchcommunitytousethedataforanalysisandmodeldevelopment.Theresultsofsuchanalysesandthemodelsandcodedevelopedcanthenbegiventohealthcaredepartmentsforvalidationontherealdata,andifeffectivecanbeputintousebycliniciansandhealthpolicy-makers.

SyntheticDataPipelineforHealthcare

TounderstandhowhealthcaredepartmentscanbenefitfromsyntheticdataweproposeapipelineshowninFigure1.Thisisaproposedsyntheticdatasharingpipelineprovidedasanillustrationofhowsyntheticdatacanpotentiallyworkwithinarealhealthcaresettingtoexpeditedataanalytics.Infuturework,weplantotestthispipelineinarealsetting.InthispipelinerealdataresideswithintheNationalHealthcareDepartmentinfrastructure.Thedatacannotbesharedexternallyduetoitssensitiveandprivatenature.HealthcaredepartmentsmayonlyhaveasmallnumberofdatasciencestaffwiththeexpertisenecessarytoapplyMLtechniquestomanyoftheirdatasets,andsotheycannotmaximisetheuseoftheirdatanordiscovertheiruseduetolackofresources.ByapplyingasyntheticdatagenerationtechniquetotherealdataalongwithSDCmeasures,asyntheticdatasetcanbeproducedandmadeavailabletotheexternalresearchcommunityinplaceoftherealdata.Externalresearchers,inlargenumbersandwithwiderangingexpertise,canpotentiallydevelopoptimalMLmodelstrainedonthesyntheticdataandsharetheperformanceoftheMLmodel,themodelitselfandthemodelspecificationwiththeNationalHealthcareDepartment.ThehealthcaredepartmentcanthentesttheMLmodelonrealdataorin-housetechnicalstaffcanrebuildthemodelaccordingtothespecificationprovidedbyresearcherswherethespecificationcanincludetheprogramcodewrittenbyresearchers,detailsoftheMLalgorithmtouse,e.g.decisiontree,supportvectormachineetc.,andtheoptimalhyperparametersettingsdeterminedduringdevelopment.Usingthesesettings,themodelcanthenberebuilt,thistimebytrainingontherealdatainsteadofsyntheticdata,whichin-housestaffhaveaccessto.

Figure1Proposedsyntheticdatasharingpipelinetoillustratehowsyntheticdatacouldbeimplementedtoexpeditehealthcaredataanalytics.

Methods

DatasetSelection

Forexperimentation,19openhealthcaredatasetshavebeenselectedfromtheUCIMachineLearningRepository[19].Missingvalueshavebeenremovedfromthedatasetseitherbyremovingfeatureswithahighnumberofmissingvaluesorremovingobservationswhereafeaturecontainsamissingvalue.TheexperimentaldatasetsandtheirpropertiesaresummarisedinTable1.Thesedatasetswereselectedtoenableananalysisofsyntheticdataperformancewhenappliedtodatasetsofdifferingvolumeanddatatypes(categoricalandnumerical).

Table1.Summaryofexperimentaldatasets.a

Dataset

No.ofAttributes

No.ofCategoricalAttributes

No.ofNumericalAttributes

No.Classes/Labels

No.ofObservations

A

BreastCancerWisconsin(Original)

9

0

9

2

683

B

BreastCancer

9

9

0

2

277

C

BreastCancerCoimbra

9

0

9

2

116

D

BreastTissue

9

0

9

6

106

E

ChronicKidneyDisease

21

12

9

2

209

F

Cardiotocography(3Class)

21

0

21

3

2126

G

Cardiotocography(10Class)

21

0

21

10

2126

H

Dermatology

34

33

1

6

358

I

DiabeticRetinopathy

19

3

16

2

1151

J

Echocardiogram

10

2

8

3

106

K

EEGEyeState

14

0

14

2

14980

L

HeartDisease

13

8

5

2

303

M

Lymphography

18

18

0

4

148

N

Post-OperativePatientData

8

8

0

3

87

O

PrimaryTumor

15

15

0

21

336

P

Stroke

10

7

3

2

29072

Q

ThoracicSurgery

16

13

3

2

470

R

ThyroidDisease

22

16

6

28

5786

S

ThyroidDisease(New)

5

0

5

3

215

Total

283

144

139

105

58,655

aEachdatasethasbeenencodedwithaletter(column1)andwillbereferencedusingthisletterfortheremainderofthepaper.

GeneratingSyntheticData

Inthiswork,weanalyseandassesstheperformanceofthreepubliclyavailablesyntheticdatagenerationtechniquesthatarebasedonwell-known,seminalworkinthearea[6-10,15,16].Thesemethodsareaparametricdatasynthesistechnique,anon-parametrictree-basedsynthesistechniquethatutilisesCART[15],andasynthesistechniquethatutilisesBayesiannetworks[16].Whilstotherapproachesexist,somearedevelopedforspecificdatasetsandproblems,e.g.SimPopsimulatespopulationsurveydata[44],andSyntheasimulatespatientpopulationandelectronichealthrecorddata[45],whereasthesetechniquesareconsideredtobemoregeneral.TheRpackage,Synthpop,developedbyNowak,RaabandDibben[17],providesapubliclyavailableimplementationoftheparametricandCARTbasedsyntheticdatagenerators.TheDataSynthesizerpythonimplementation,developedbyPing,StoyanovichandHowe[16],providesapubliclyavailableimplementationoftheBayesiannetworkbasedsyntheticdatagenerator.Theseimplementationshavebeenutilisedinthisexperimentalwork.

AttributesaresynthesisedsequentiallyinboththeparametricandCARTmethods.Thesyntheticvaluesforthefirstattributearesynthesisedusingarandomsamplefromtheoriginalobserveddatasinceithasnopredictorsfrompreviouslysynthesisedattributesinthedataset.Whensynthesisingattributes,bothcategoricalandnumerical,withthenon-parametricmethod,theCARTmethodisapplied.CARTisappliedtoallvariablesthathavepredictors,i.e.attributespriortotheminthesequence,anddrawsfromtheconditionaldistributionsfittedtotheoriginaldatausingCARTmodels.Theparametricmethodsynthesisesattributebasedondatatype.Numericalattributesaresynthesisedusingnormallinearregression.Categoricalattributesaresynthesisedusingpolytomouslogisticregressionwheretheattributehasmorethantwolevels,whilstlogisticregressionisappliedtosynthesisebinarycategoricalvariables[17].TheBayesiannetworkmethodofsynthesisingdatalearnsadifferentiallyprivateBayesiannetworkthatcapturescorrelationstructurebetweenattributesintherealdataanddrawssamplesfromthismodeltoproducesyntheticdata[16].

SupervisedMachineLearningwithRealandSyntheticData

AkeymeasureofdatautilityofasyntheticdatasetforthepurposeofMListodeterminehowwellasupervisedMLmodeltrainedonsyntheticdata,performswhentaskedwithclassifyingrealdata.ThiswilldeterminewhethersupervisedMLmodelswillberobustenoughtoclassifyrealdataexamplesifonlysyntheticdataisprovidedforthetrainingofthesemodels.

ToevaluatewhethersyntheticdatasetscanbeusedasavalidalternativetorealdatasetsinML,foreachofthe19datasets(Table1),fivedifferentclassificationmodelsweretrained.Initiallythemodelsweretrainedandtestedontherealdatatoobtainaperformancebenchmark.Subsequently,aclassifierwastrainedoneachofthesyntheticdatasets,generatedusingparametric,CARTandBayesiannetworktechniques,andthentestedwiththerealdata.Modelsaretestedonrealdataonly,todeterminewhetheramodeldevelopedbytrainingonsyntheticdatacanbeputintousebyhealthcaredepartmentsandusedtoaccuratelyclassifynew,realexamples.

Therangeofmodelsappliedtoeachdatasetwere:stochasticgradientdescent(SDG)decisiontree(DT),k-nearestneighbors(KNN),randomforest(RF),andsupportvectormachine(SVM).Thisselectionofalgorithmswasappliedtodeterminehowwelleachperformedwhentrainedwiththerealdatacomparedwiththesyntheticdata,withbothtestedonrealdata.

TheclassifierswereimplementedusingPython’sScikit-Learn0.21.3machinelearninglibraryandareasfollows:

StochasticgradientdescentclassificationwasimplementedusingSGDClassifier,asimplelinearclassifier,withloss=“hinge”,random_state=0andallotherparameterssettotheirdefaults.

DecisiontreeclassificationwasimplementedusingDecisionTreeClassifier,anoptimisedversionofCART,withcriterion=“gini”,max_depth=10andrandom_state=0andallotherparameterssettotheirdefaults.

K-NearestNeighborsclassificationwasimplementedusingKNeighborsClassifierwithn_neighbors=10,weights=‘uniform’,leaf_size=30,p=2,metric=‘minkowski’,n_jobs=2andallotherparameterssettotheirdefaults.

RandomForestclassificationwasimplementedusingRandomForestClassifierwithcriterion=“gini”,max_depth=10,min_samples_split=2,n_estimators=10,random_state=1andallotherparameterssettotheirdefaults.

SupportVectorMachineclassificationwasimplementedusingSVCwithC=1.0,degree=3,kernel=‘rbf’,probability=True,random_state=Noneandallotherparameterssettotheirdefaults.

Fortrainingandtesting,Python’sScikit-Learn0.21.3ShuffleSplitrandompermutationcross-validatorwasusedwith10splittingiterationsandatrain/testsplitof75/25.Categoricalattributesweretransformedintoindicatorattributesusingone-hotencoding.

StatisticalDisclosureControl

Syntheticdataisconsiderednottocontainrealunitsandthereforetheriskofdisclosureofarealpersonisconsideredtobeunlikely[46].Whilstunlikely,thescenariowheresomeofthegeneratedsyntheticdataisverysimilartotherealdata,resultinginpotentialdisclosurerisk,mustbeconsideredandwhereadditionalprotectionscanbeappliedtosyntheticdataitisplausibletodoso.Additionalstatisticaldisclosurecontrol(SDC)measures,beyonddatasynthesis,canbeappliedasaprecautionarymeasuretoaddfurtherprotectionstosyntheticdatabyreducingtheriskofreproducingrealpersonrecordsandreplicatingoutlierdata,thus