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RoleofEconomicEpidemiology: WithSpecialReference to HIV/AIDS SenelaniDorothyHoveMusekwa

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RoleofEconomicEpidemiology: WithSpecialReference to HIV/AIDS

SenelaniDorothyHoveMusekwa NUSTAIMS BulawayoCapeTown ZimbabweSouthAfrica EconomicEpidemiologyWorkshop Uganda: 3August2009

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Outlineofpresentation

Definitions Trend/Aim/Benefit Prevalencedependence Effectsofindividualbehaviour EconomicimpactofHIV/AIDS Conceptsfrommathematical epidemiologicalmodels Measuringeconomicimpact

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Outline…….

Economicevaluationconcepts Conclusion

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WhatisEconomicEpidemiology?

Economicepidemiology isafieldatthe intersectionofepidemiologyandeconomics Itspremiseistoincorporate principlesofindividualbehavior incentivesforhealthybehavior(Wikipedia) resourceoptimization simpleeconomics intoepidemiologicalmodelsand thedynamicsofinfectiousdiseases intohealtheconomics

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Epidemiology

Itisthebasicscienceofpublichealth whichisthescienceandartof preventingdiseases prolonginglife promotinghealth throughorganisedeffortsandinformed choices ofgovernments,individuals, communities,societiesandorganisations (bothprivateandpublic)(Winslow,1920)

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Epidemiology

DEFINITION: Thestudy ofthe distribution,frequency and determinants ofhealthproblemsand diseaseinhumanpopulation PURPOSE: Toobtain,interpretand usehealthinformationtopromote healthandreducedisease(that’s publichealth) Publichealth meanspublicpolicy

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Economics

Economics isthesocialscience that studiestheproduction,distribution,and consumption ofgoods andservices. Economicsaimstoexplainhoweconomies workandhoweconomicagents interact. (Wikipedia) Economicsplaysabigroleinpublic policy whileepidemiologysays alotabout thedynamicsofinfectiousdiseases

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Whatisthetrend?

Epidemiologicalmodelsdonotrealtake accountofeconomicconstraintsor incentivesfacedbyindividualsandpolicy makers Economicmodelsmostlydonot incorporatethedynamicsofdisease. Biologicalandeconomicepidemiology makedifferentpredictionsofdisease

  • ccurrencebecauseoftheirdifferent

predictionsabouttherelationshipbetween preventionandprevalence(Philipson, 1999)

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Hazardrateintoinfectionisanincreasing functionofprevalenceinepidemiologicalanalysis whileitisadecreasingfunctionofprevalencein economicalanalysis Morepeopleinfectedinthepopulationleadsto moresusceptibles infectedlater Susceptibles facealargerriskofinfectionand thereforetheirdemandforpreventionbecomes highandthusreduceinfectionhazard Norealcollaborativeworkbetweenbiologists, economistsandmathematicalepidemiologists (Kleinetal2007)

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Aim

Haveaninterdisciplinaryapproachto managethecomplexinteractionof mathematical,economical, epidemiologicalandbiological considerationsintheemergence, persistenceandspreadofinfectious diseases

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Benefits:Epidemiologicalmodels

Provideafoundationforpublicpolicy modelsofdiseasetreatmentand preventionprograms Estimatediseaseincidenceandprevalence (numberofindividualsperunittimewho areinfected) Identifygroupsofthepopulationwhichare mostatriskofcontactingthedisease Estimateparametersdefiningstrategiesto counteracttheepidemic

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Benefits:Policymakers

Requiretomakeinformeddecisions to determinethebestwayofallocatingscarce resourcesforthedifferentprogramsof preventionandtreatment Needtoknowthebenefitandcostof eachprogram thatproducesthegreatest reductionininfections,morbidityand mortalitygivenresourceconstraints

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Benefitscontd….

Reasonableassessmentsof programcostsandbenefitsare requiredtomakerationalpolicy decisions Improvespolicyresponsesto epidemicdiseasesbyproviding cleartoolsforthinkingabouthow certainactionscaninfluencethe spreadofdiseasetransmission.

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Benefitscontd…. Optimalstrategiesand policiesareneededtocontrol thespreadofdiseases

Economicevaluation conceptsare thereforerequiredtohelptoidentify, measure,comparecostsand consequencesofalternatestrategies

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Sowhat?

Economicepidemiologystrivesto incorporatedifferenttypesofbehavior responses(individual,policymaker)into epidemiologicalmodelstoenhancea model’sutilityinevaluatingcontrol measures. Needunderstandwhatisinvolvedand howitcanbedonetomakesurethatthis ‘marriage’ betweeneconomicsand epidemiologycanwork

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PrincipleofIndividualBehaviour

Thefieldisdependentontheideaof prevalence Epidemiologicalanalysisdiscusseshow variouspatternsofbehaviouraffectthe progressionandoccurrenceofthedisease butdoesnotanalysetheimplicationsand effectsofthisbehaviourchange Limitingthespreadofadiseaseatthe populationlevelrequireschanging individualbehavior,

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Thisdependsonwhatinformation(general andspecific)individualshaveaboutthe levelofriskbecauseindividualschange theirbehaviorastheprevalenceofa diseasechanges Decisionsaffectinghealthalsodependant

  • nobjectivesandconstraints– notnormal

takencareofinhealthpolicyformulation – economicsofthehome

  • therthingstotakecare
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Whendiseasedisappearsthe demandforvaccinesalsodoesso Declineinvaccinationthenallowsthe diseasetoreturn Supplysideisalsoaffectedsince demandforthesupplierisalso eradicated

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Example

Massivecampaignsofboiling drinkingwater,washyourhands beforeyoueat,don’tshake hands,etctoreducecholera transmissioncanreducethe effectsoftheepidemicandthis mightleadtorelaxationofthe abovecampaigns

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Peopletendtoignoreadiseaseifriskis low,butiftheriskofinfectionishigher, individualsaremorelikelytotake preventiveaction. Ifthepathogenismoretransmissible,like HIV,thegreatertheincentiveistomake personalinvestmentsforcontrol. Similarlyifthereisaloweredriskof disease,eitherthroughsomeinterventions likevaccinationorbecauseoflowered prevalence,individualsmayincreasetheir risktakingbehavior.

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Modelssuggestedthatthe introductionofhighlyactive antiretroviraltherapy(ART),which significantlyreducedthemorbidity andmortalityassociatedwith HIV/AIDS,mayleadtoincreasesin theincidenceofHIVastheperceived riskofHIV/AIDSdecreased(Blower SMetal,2000)

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Transmissionprocess(a)

Susceptible Infected Recovered/ Immune Onepersonacquiresinfectioninthecommunityandtransmitsto threeneighbours

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Transmissionprocess(b)

Susceptible Infected Recovered /Immune

Threepersonsinfectedbyone

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Transmissionprocess(c)

Susceptible Infected Recovered/ Immune

Transmissioncontinues

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Transmissionprocess(d)

Susceptible Infected Recovered /Immune

Transmissioncontinues(Indexcaserecovers)

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Transmissionprocess(e)

Susceptible Infected Recovered/I mmune

Transmissioncontinues(morerecoveries)

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Transmissionprocess(f)

Susceptible Infected Recovered/ Immune

Thediseaseclearsfromthecommunity

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Transmissionprocess(g)

Susceptible Infected Recovered/I mmune

Supposeininfectivesetsinthecommunityfromelsewhere

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Transmissionprocess(h)

Susceptible Infected Recovered/ Immune

Noinfectionwilloccurduetoherdimmunity

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Effectsofindividualbehaviour

Positiveornegative Governmentintervention“toalign theprivatecostsandbenefitswiththe socialcostsandbenefitsofdecisions” (GersvitzandHammer,2003)inthe formofsubsidiesforpreventivesand treatment

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Publicinterventions:

Behavioralresponsehaveimportant implicationsforthetimingofpublic interventions,becauseprevalenceand publicsubsidiesmaycompetetoinduce protectivebehavior(Geoffard,etal1996). Pricesubsidiesandmandatory vaccination limitedsincehigher vaccinationcoverageofindividualsinthe programmightlowertheincentiveofthose

  • utsidetheprogramtobevaccinated
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Demandrisesforthosewhoare subsidizedanddemandfallsforthose notcovered. Prevalencecompeteswithpublic interventionininducingprotective activity

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Ifprevalenceinducesthesamesortof protectivebehavioraspublic subsidies,thesubsidiesbecome irrelevantbecausepeoplewillchoose toprotectthemselveswhen prevalenceishigh,regardlessofthe subsidy,andsubsidiesmaynotbe helpfulatthetimeswhentheyare typicallyapplied.

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Externalities

Individual’sactionresultsinbenefitsorcoststo

  • thers

Preventionandtherapyinvolveexternalitieseg masssprayingreducesmosquitobutisitgoodfor theneighbour’shealthorenvironment Areindividualandsocialincentivesforprevention andtreatmentthesame? Whataretheirobjectivesandconstraints (economicsofthehome,otherimportant

  • bjectives– lifegoeson)

Isittoavoidinfectingothersegyourspouse,the public,etcorforselfishreasons

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Preventionintimesoflove

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Preventioninbusiness

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Factorsinfluencingbehaviour responses

Environmentalfactors servicesand policies Socialfactors– peers,family,role models Personalfactors– knowledge,self efficacy,risk,riskperception

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EconomicImpactofHIV/AIDS EconomicimpactofHIV/AIDS isbasedonthedirect monetaryvaluesthatare incurredastheepidemicruns itscourse. Costsinvolvedaffectsthe patient,theworker,family,the government

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Adeclineinsavingsandinvestment (fromtherelocationofexpenditures towardsmedicalcare), Consequently,thereisneteffecton thegrowthrateofpercapitaGDP

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ThelongruneconomiccostsofAIDS arealmostcertaintobemuchhigher andpossiblydevastatingifwe emphasizetheimportanceofhuman capitalandtransmissionmechanism acrossgenerationsinanyeconomy.

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Theformationofhumancapital,which shouldbethoughtofastheentire stockofknowledgeandabilities embodiedinthepopulation,playsa leadingroleinpromotingeconomic growth. AIDScanseverelyretardeconomic growtheventothepointofleadingto aneconomiccollapsesinceAIDSis primarilyadiseaseofyoungadults.

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Intermsoftheeconomicpolicy,AIDShas particularlytwoimportantimplications.

  • Bykillingoffmainlyyoungadults,AIDS

alsoseriouslyweakensthetaxbase,and soreducestheresourcesavailabletomeet thedemandsforpublicexpenditures, includingthoseaimedataccumulating humancapital,suchaseducationand healthservicesnotrelatedtoAIDS pressureoneconomy.

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  • Slowergrowthoftheeconomy

meansslowergrowthofthetaxbase, aneffectthatwillbereinforcedifthere aregrowingexpendituresontreating thesickandcaringfororphans. Asaresult,thestate'sfinanceswill comeunderincreasingpressure.

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MeasuringtheEconomic Impact

Baseallouranalysisonamathematical model,wherepreventionandtreatment havebeenaugmentedinthefightagainst thepandemic. Developthecostfunctionmodelwhich capturesallcostsoftherapyand progressiontoAIDSforallthosewhoare infectedatthebeginningoftreatment

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TheCosts

Types: direct,indirect,intangible Lossofproductivitydueto prematuredeathofinfected individuals sicknessofinfectedindividuals timelosttothecaregiver Strengtheningthehealthcaresystem topreventspread

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Costs

Lossofskilledworkforce Retraininganewworkforce Screeningpeoplefortheinfection Screeningofbloodproducts Preventionseg verticaltransmission, educationalcampaigns Hospitalization Painofsufferingtothepatientsandtheir families intangible

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Costs

Postinfectioncounseling, Trainingpeereducators,printingbooklets andotherrelatedmaterial. Homebasedcare Runningtheclinicandotherrelated administrativeissuessuchasfollowupof defaultersbyphoning Researchanddevelopment MeasuringtheEconomicImpact+ Economicalepidemiology???

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TheEconomicevaluation

“ Thecomparativeanalysisofalternativecourses

  • factionintermsofboththeircostsand

consequencesinordertoassistpolicydecisions” (Drummondetal,1997) Economicevaluationis “choosingthe cheapest”.

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Mainconcepts

Identify,measure,comparecostsand consequencesofalternative strategies,policyinterventionsand allocatelimitedresourcesas efficientlyaspossible Technicalefficiency:meetinga givenobjectiveatleastcost Allocationefficiency:producing exactlywhatsocietywantsorexpects

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MeasuresofProgramEffectiveness MeasuresofProgramEffectiveness

Infectionsaverted Expectedsurvivalincreases Lifeyearsgained

  • e.g.,episodesofillness,

e.g.,episodesofillness, infections,durationofdisability(e.g., infections,durationofdisability(e.g., yearsofsight) yearsofsight)

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Utility

  • lifeyearsx

lifeyearsx utilityscores utilityscores

  • lifeyearsx

lifeyearsx utilityscores utilityscores

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Informationfromepidemiological model

EstimatedOutcomesofWHOrecommendations

19.0 7.1 13.3 8.6 7.1 5 10 15 20 25 Personyears losttoHIV/AIDS (1000s) Lifeyearssaved (1000s) Lifeyearssaved perperson treated YearsonART (1000s) NumberofCD4 testappts (1000s)

BestestimatesofeffectofWHOrecommendations

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Meanageatdeath symptomaticinitiation 5 10 15 20 25 30 35 40 45 50 NoAIDS Treatment ART (Optimistic effect) ART (Estimated effect) ART (Pessimistic effect) Age(years)

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Impactofinitiationstrategyonmorbidity 861 462 487 100 200 300 400 500 600 700 800 900 1000 NoAIDSTreatment Syndromicinitiation WHOGuidelines Numberof"sickdays"(1000s)

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Measurementofcosts

Innaturalphysicalunitsegtime,$ Fixed,variable,total

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Averagevsmarginal MarginalvsIncremental

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CostperQALYgained

Letcostwithintervention=CI Letcostwithnointervention=CNI QALYwithintervention=QALYI QALYwithnointervention=QALYNI CostperQALYgained Alwaysstartwithnointerventiontointervention, likeR0 toRe

  • =
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FormsofEconomicEvaluation

  • !"!

##

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CostAnalysis

Measuresorestimatetheresources consumedbyaparticularintervention strategy Helpspolicymakerstodecide whethertheyhavesufficient resourcestoaffordaparticular interventionstrategy

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Example:Costperlifesaved (CPLS)

Thisisgivenby DrugA:probabilityofavoidingdeath changesfrom0.3to0,4,costper treatment$6 DrugB:probabilityofavoidingdeath changesfrom0.3to0.35,costper treatment$5 CPLS=$60forAand$100costper treatment$5

  • =
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  • Determinestheleastcostly

interventionamongequallyeffective interventions Basedonlycostscomparisons Required:Leastcostalternative Whenthereisvariationintermsof costsandconsequencesweneed CBA,CEAandCUA

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Expressesbothcostsofinterventionsand theirconsequencesinmonetaryterms Result:Netbenefitorcostbenefitratio. Assigningamonetaryvaluetoa consequencelikehumanlifesavedis difficultandthereforecontroversialandnot used

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!"!

Comparesthecostsofinterventionsperhealth

  • utcomeachieved

Nomonetaryvalueisassignedtooutcomes, resultsarepresentedintheformofcostper healthoutcome likecostperHIVinfection averted, costperlifesaved Veryusefulin identifyingthemost effectiveintervention fromasetofalternatives

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CEAcontd……..

HowtodecidebetweenstrategyAandB EffectivenessofB=EffectivenessofA→ useCMA EffectivenessofB>EffectivenessofA, CostB <CostA,→ B isdominant EffectivenessofB>EffectivenessofA, CostB >CostA,→ Makeadecision How????

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Costeffectivenessratio(CER)

Tomakeadecisiononwhichinterventionto choose,calculateacosteffectivenessratio (CER). ThemostcommonlyCERsusedarethe:

  • Averagecosteffectivenessratio(ACER)

Incrementalcosteffectivenessratio(ICER)

Thenextquestionis:$%" "&'

  • =
  • −

− =

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CEAcontd……….

Thereisno‘magic’ cutoffnumberthat establisheswhetherornotaninterventionis ‘costeffective’. Itwilldependonwhatistermedthedecision maker’s‘ceilingratio’. Theceilingratiocanbeinferredfromtheamount thatdecisionmakersarewillingtopay. Tomakeadecision:

IfICERoftheprogram≤ ceilingratio→ adoptthe program IfICERoftheprogram>ceilingratio→ donotadoptthe program

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CEA

ThecosteffectivenessacceptabilityPlane:

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Example

Interve ntion Averag ecosts ($) QALY (average effective ness) ACER ICER Int:1 100 2 50

  • Int:2

300 4 75 200 Int:3 200 2 100 ∞ Int:4 150 6 25 12.5

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CostutilityAnalysis

Outcomesaremeasuredinhealthy years,towhichavaluewillbe attached. Considersqualityoflife aswellas quantityoflife usingacommonunit. Qualityadjustedlifeyears(QALYs) Takesintoaccounttheimpactof interventionsonthequalityand quantityoflife

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Example

Eg 1yearwithperfecthealthisequally desirableas2yearswitha50%diminished qualityoflife Mostappropriateifqualityoflifeisan importantoutcomeandwhenintervention affectsbothmorbidity andmortality Disabilityadjustedlifeyear(DALY)widely usedineconomicevaluationofHIV preventioninterventionsoutsideUSA

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CostutilityAnalysis

InCUA,theoutcomesaremeasuredinhealthy years,towhichavaluehasbeenattached. CUAismultidimensional andincorporates considerationsofqualityoflife aswellasquantityof life usingacommonunit. Result:Costperunitofconsequence(e.g. cost/QALY).

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CostbenefitAnalysis

CBAtrytovaluetheoutcomesinmonetaryterms,so astomakethemcommensuratewiththecosts. Result:Netbenefitorcostbenefitratio. CBAsrarelyusedinhealthcare.

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CostutilityAnalysis(CUA)

Outcomesaremeasuredinhealthy years,towhichavaluewillbe attached. Considersqualityoflife aswellas quantityoflife usingacommonunit. Qualityadjustedlifeyears(QALYs) Takesintoaccounttheimpactof interventionsonthequalityand quantityoflife

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CUA

Eg 1yearwithperfecthealthisequally desirableas2yearswitha50%diminished qualityoflife Mostappropriateifqualityoflifeisan importantoutcomeandwhenintervention affectsbothmorbidity andmortality Disabilityadjustedlifeyear(DALY)widely usedineconomicevaluationofHIV preventioninterventionsoutsideUSA

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CUA

Disabilityadjustedlifeyearsaverted byeachstrategy Projectthebenefitsofimplementing particularstrategy Assesstheextenttowhichtreatment improvespopulationhealth

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Adjustingfortiming

Discounting(3% 5%)

Prefertohavebenefitsnowandbearcostsin

thefuture– ‘timepreference’

Rateoftimepreferenceistermed‘discountrate Toallowfordifferentialtimingofcosts(and

benefits)betweenprogrammesallfuturecosts (andbenefits)shouldbestatedintermsoftheir presentvalue usingdiscountrate.

Thus,futurecostsgivenlessweightthan

presentcosts.

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8ElementsofCEA

Aclearstudyperspective,timeframe, andanalytichorizon Anexplicitlydefinedstudyquestion Relevantassumptionsunderlyingthe study Detaileddescriptionsoftheinterventions Existingevidenceoftheinterventions' effectiveness

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8ElementsofCEAcontd….

Properidentificationofallrelevantcosts:

decidewhethertoincludeorexcludeproductivitylosses applyappropriatediscountrate confirmthatincludedcostsarerelevanttoperspective

Anappropriatechoiceofoutcome:

calculateasuitable!( report$!( results(unlesstheonlycomparatoris

baseline)

conductsensitivityanalyses

Acomprehensivediscussionoftheresults:

dealwithissuesofconcern addressimplicationsofunderlyingassumptions

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Conclusion

Epidemiologicalmodelstakingaccountof economicconstraintsorincentivesfaced byindividualsorinstitutionswillbehelpful Economicmodelstakingintoaccountthe spatialandtemporaldynamicsofdisease willbemorepractical. Changeofbehaviour reducesthe economicimpactoftheepidemic Thereforethereisneedtostrengthenthe marriage betweenEconomicsand Epidemiologytoenablepolicymakersto makeinformeddecisions

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EconomicModelling:With special referenceto HIV/AIDS

Senelani DorothyHoveMusekwa NUSTAIMS Bulawayo CapeTown ZimbabweSouthAfrica EconomicEpidemiology Uganda:3August2009