信息不对称AsymmetricInformation(卫生经济学)课件

信息不对称AsymmetricInformation信息问题InformationProblems患者——缺乏信息，也没有能力识别质量Patients—lackofinformationandinabilitytodiscernquality保险方——缺乏参保者的健康状况信息Insurers—lackofinformationaboutindividual’shealthbackground逆向选择Adverseselection假设有10个低风险的人和10个高风险的人，高风险的人预期的医疗保健费是1000美元，低风险的人预期的医疗保健费是100美元。医疗保险费的确定基于平均的预期医疗保健费，也就是550美元Supposethereare10lowriskpeopleand10highriskpeople,thehighriskpeople’sexpectedhealthcareexpenditurewillbe$1000,thelowrisk’swillbe$100.Thehealthinsurancepremiumisbasedonaverageexpectedexpenditure,whichis$550.

信息不对称AsymmetricInformation信息1逆向选择AdverseSelection保险公司无法区分风险高和风险低的人。保险费只反映了两类人的平均风险。因此高风险的人将购买保险，因为此时的保险费低于完全依照他们的风险确定的保险费。而低风险的人可能不会购买保险，因为此时的保险费高于完全依照他们的风险确定的保险费。Theinsurancecompanyisunabletodistinguishbetweenhighandlowrisks.Theinsurancepremiumonlyreflectstheaverageriskofthetwogroups.Then,thehighriskgroupwillpurchaseinsurancesinceapremiumbasedontheaverageriskislowerthanapremiumbasedsolelyontheirownrisk.Thelowriskindividualsmaynotpurchaseinsurancesinceapremiumbasedontheaveragewouldbegreaterthantheirownrisk-basedpremium.逆向选择AdverseSelection保险公司无法区分2逆向选择AdverseSelection逆向选择将会导致某些人购买医疗保险Adverseselectionwouldresultinabiasedsampleofthosethatpurchasehealthinsurance更多的高风险个人将购买保险Predominantly,morehighriskindividualswouldpurchaseinsurance“柠檬”法则TheLemonsPrinciple高风险的人驱逐低风险的人直至市场不存在Thebaddrivesoutthegooduntilnomarketisleft逆向选择AdverseSelection逆向选择将会导致3柠檬法则TheLemonsPrincipleAkerlof(1970)用信息不对称的观点分析二手车市场Akerlof(1970)usedtheideaofasymmetricinformationtoanalyzetheusedcarmarket二手车的质量千差万别Usedcarsavailableforsalevaryinquality对称不信息Asymmetricinformation卖者比买者更了解车子的质量Thesellersknowbetterthetruequalityoftheircarsthanthebuyers有9辆车供出售Thereare9carsforsale质量(Q)=0,¼,½,¾,1,1¼,1½,1¾,2卖者了解每辆车的质量Seller(owner)knowseachcar’squality买者只知道质量的分布Buyeronlyknowsthedistributionofquality柠檬法则TheLemonsPrincipleAkerl4柠檬法则TheLemonsPrinciple卖者的保留价值是$1000xQ

Sellerhasareservevalue=$1000xQ买者的保留价值是$1,500xQ

Buyerhasareservevalue=$1,500xQ雇佣一个拍卖人报价。拍卖人找到一个需求量等于供给量的价格就成交Anauctioneerishiredtocalloutprices.Salestakeplacewhentheauctioneerfindsapricethatmakesquantitydemandedequalquantitysupplied我们现在进行这个拍卖游戏Wedothesalesgametogetherinclass柠檬法则TheLemonsPrinciple卖者的保留5柠檬法则TheLemonsPrinciple如果信息对称，买者和卖者都不清楚具体的质量，他们只知道车子的平均质量，此时二手车市场能否存在？市场价格是多少？Ifinformationhadbeensymmetric,bothownersandbuyerswereuncertainofthequality,theyonlyknowtheaveragequalityofcars,thenisthereamarketfortheusedcars?Whatwouldbethemarketprice?柠檬法则TheLemonsPrinciple如果信息对6柠檬法则的应用：医疗保险ApplicationofTheLemonsPrinciple:HealthInsurance信息不对称Informationasymmetry潜在的参保者比医疗保险公司更了解自己将来可能的医疗保健支出Thepotentialinsuredpersonknowsmoreabouther(his)expectedhealthexpendituresinthecomingperiodthandoestheinsurancecompany.具体地讲Morespecifically参保者知道自己将来的医疗费用（类似于二手车的车主）Insuredknowsher(his)futureexpenditureexactly(similartotheownerofthecars)保险公司只了解所有参保者的医疗费用的分布（类似于买车的人）Insurancecompanyknowsonlythedistributionofexpendituresforallinsuredpersons(similartothebuyerofthecars)柠檬法则的应用：医疗保险ApplicationofThe7柠檬法则的应用：医疗保险ApplicationofTheLemonsPrinciple:HealthInsurance医疗保险市场有5个人Thereare5personsinhealthinsurancemarket预期的医疗费用＝0,¼,½,¾,1Expectedexpenditure=0,¼,½,¾,1平均医疗费用＝½Averageexpenditure=½我们再做一个游戏看医疗保险市场是否存在Wedothegameagaininclasstocheckifthereishealthinsurancemarket如果信息对称，参保者和保险公司都只知道风险的分布，那将会怎样？Ifinformationhadbeensymmetric,bothinsuredandinsurancecompanyonlyknowthedistributionofexpenditure,then?柠檬法则的应用：医疗保险ApplicationofThe8代理关系——委托代理问题AgencyRelationship—ThePrincipalAgentProblem代理关系Agencyrelationship委托方委托另一方，也就是代理方作出决定Aprincipaldelegatesdecision-makingauthoritytoanotherparty,theagent信息不对称和代理问题是相关的现象Asymmetricinformationandagencyarecloselyrelatedphenomena委托代理问题ThePrincipalAgentProblem怎样确定医生作出了最符合患者利益的决策Howtodeterminethephysicianisactinginthepatient’sbestinterests代理关系——委托代理问题AgencyRelationshi9供给诱导需求Supplier-InducedDemand供给诱导需求问题TheSupplier-InducedDemandproblem医生具有影响需求的利益驱动Thephysicianhasafinancialinteresttoinfluencethedemand.医生可以通过提供不准确的信息“创造”需求Thephysiciancan“create”thedemandbyprovidingthebiasedinformationtothepatient供给诱导需求问题源于信息不对称TheSIDproblemresultsfromasymmetricinformation患者和保险方都缺乏作出关于医疗方面的决策的必要信息Bothpatientsandinsurerslackthenecessaryinformationtomakemanymedical-relateddecision患者依赖于医生的建议和他们所提供的服务Thepatientdependsuponthephysicianforbothadviceandservice供给诱导需求Supplier-InducedDemand10供给诱导需求Supplier-InducedDemand传统的经济学模型Thetraditionaleconomicmodel传统的经济学模型假设医生是患者完美的代理人，可以推出其他条件不变，供给的增加将降低医生的收费，从而降低医生的收入。Thetraditionaleconomicmodel,whichassumesthephysicianisaperfectagentforthepatient,wouldpredictthatanincreaseinsupply,otherthingsbeingequal,wouldresultinadeclineinphysician’sfees,andconsequentlyphysicianincomes.现实的观察正好相反Theobservationinrealityisopposite需要更合理的理论解释医生的行为Needalternativetheorytostudyphysicianbehavior供给诱导需求Supplier-InducedDemand11S1S0D0E0E1供给诱导需求Supplier-InducedDemand传统的经济学模型Thetraditionaleconomicmodel供给量增加价格下降MQ0Q1P0P1PmS1S0D0E0E1供给诱导需求Supplier-Indu12供给诱导需求Supplier-InducedDemand供给诱导需求的价格刚性模型ThepricerigiditymodelofSID为什么竞争的市场会出现诱导需求？一种解释是假设医疗价格倾向于刚性Oneapproachthatcanexplaindemandinducementwithinthecontextofacompetitivemarketmodelistoarguethatpricestendtoberigid随着供给增加，为了保持固定的价格，医生具有增加需求的激励Assupplyincreases,inordertofixtheprice,thephysicianhasincentivetoinducedemand但是这个理论只能解释为何价格没有下降，但不能解释为何价格上升Butthismodelcanonlyexplainwhypricedoesn’tgodownandcan’texplainwhypricegoesup供给诱导需求Supplier-InducedDemand13D1供给诱导需求Supplier-InducedDemandSID的价格刚性模型ThepricerigiditymodelofSID供给量增加价格不变S1E0MQ0Q2P0PmS0D0E2D1供给诱导需求Supplier-InducedDema14供给诱导需求Supplier-InducedDemandSID的目标收入模型ThetargetincomemodelofSID尽管医生的供给快速增加，医疗价格仍然上升Thepriceofhealthcareincreasesdespiterapidincreaseinphysiciansupply目标收入模型用以解释医生收费的快速上升Thetargetincomemodelisusedtoexplaintherapidincreaseinphysicianfees.在目标收入假设下，医生供给的增加导致收费的上升以保证目标收入，或者医生将诱导患者的需求以保证目标收入Underthetargetincomehypothesis,increaseinsupplyofphysiciansleadtohigherfeesinorderforearningtobemaintained,orphysicianwillinducedemandtomaintainthetargetincome供给诱导需求Supplier-InducedDemand15供给诱导需求Supplier-InducedDemandSID的目标收入模型ThetargetincomemodelofSID供给量增加价格上升D1S1E0S0D0E2MQ0Q2P0PmP1供给诱导需求Supplier-InducedDemand16供给诱导需求Supplier-InducedDemandSID的目标收入模型ThetargetincomemodelofSID目标收入假设的主要证据是医生/人口比率和医生收费呈正相关Themajorevidencefortargetincomehypothesisisthatphysician/populationratiosarepositivelyrelatedtophysicianfees医生诱导需求的范围和价格水平取决于医生期望的收入目标Theextentofthedemandthephysiciancancreateandthepricethatwillbeestablishedarebaseduponwhattargetincomethephysiciandesires目标收入水平取决于当地的收入水平，尤其是其他医生和专业人士的收入水平Thetargetincomeisdeterminedbythelocalincomedistribution,particularlywithrespecttotheincomeofotherphysiciansandprofessionals供给诱导需求Supplier-InducedDemand17供给诱导需求Supplier-InducedDemandSID的利润最大化模型MQ1Q2P2PmP1MR2D1MC1MR1D2MC2供给诱导需求Supplier-InducedDemand18供给诱导需求Supplier-InducedDemandRoemer&Shain提出，一个地区增加床位的供给创造对床位的需求。为什么？供给诱导需求Supplier-InducedDemand19(1)短缺的存在如果制定的医疗价格低于均衡水平，即在P0处，S0表明床位供给，医院利用为Q0。在P0价格上，就会出现Q3到Q0的过度需求。如果床位供给从S0增加到S1，从S1增加到S2，再至S3，医院利用就会从Q0增加到Q3。供给诱导需求Supplier-InducedDemandS1S2S3S0Q0Q1Q2Q3DMP0Pm解释一(1)短缺的存在供给诱导需求Supplier-Induc20(2)预计需求扩大图中S0&D0表示起始供求曲线，Q0为医院服务利用。如果床位供给增加到S1，医院服务利用增加到Q1，这种情况表明供给创造新的需求D1，相反，床位供给是建立在对需求增长的预测基础上。供给诱导需求Supplier-InducedDemandD0S0D1S1MQ0Q1Pm(2)预计需求扩大供给诱导需求Supplier-Indu21患者的往返成本发生了变化。如果增加的床位建在靠近预期患者的新型较小医院，到医院的往返成本将降低，这时，床位供给的增加并不创造新的需求，而是降低非货币成本(如路途的时间成本），使患者医疗总价格下降，从而使患者沿着其需求曲线向下移动。如图：解释二MQ1Q2P1P2Pm供给诱导需求Supplier-InducedDemand患者的往返成本发生了变化。如果增加的床位建在靠近预期患者的新22医生通过收治患者入院来提高效益。解释三供给诱导需求Supplier-InducedDemand还有其他解释吗？医生通过收治患者入院来提高效益。解释三供给诱导需求Supp23供给诱导需求Supplier-InducedDemand一项研究表明，平均每人受诊数和一定人口拥有的医生数量呈正相关，如一定人口拥有的外科医生数每年增加10％，则手术例次增加3％。另一项研究表明，医生按服务项目收费得到补偿时，外科手术率是比较高的。某研究对有同样保险赔付的雇员做了比较。其中一组按人头预付计划（capitation)，另一组按服务项目收费(fee-for-service)。结果发现住院手术处理率在按人头付费为3.9,而在按项目收费中为7.0。在手术处理率的差别中，有1/3是阑尾切除术，扁桃体摘除术，女性外科手术（如剖腹产）等造成的。供给诱导需求Supplier-InducedDemand24供给诱导需求Supplier-InducedDemand供给诱导需求Supplier-InducedDemand25供给诱导需求Supplier-InducedDemand供给诱导需求Supplier-InducedDemand26供给诱导需求Supplier-InducedDemand供给诱导需求的识别问题TheidentificationproblemofSID实证研究中，诱导需求的影响无法用计量方法识别Intheempiricalwork,theSIDeffectcannotbeeconometricallyidentified很难区分患者的需求和医生诱导的需求Itishardtodistinguishbetweenpatient’sdemandandphysician’sinduceddemand供给诱导需求Supplier-InducedDemand27供给诱导需求Supplier-InducedDemand供给诱导需求的成本ThecostsofSID时间成本Timecost声誉下降Reputationloss“心理精神”成本“psychic”cost供给诱导需求Supplier-InducedDemand28供给诱导需求Supplier-InducedDemand避免医生创造需求的方法：增加患者受教育水平可能会降低医生创造额外需求的能力。当患者被建议做手术时，应从保险公司或其他医生处获得更多信息。向医生提供经济刺激以避免不必要的手术。这些经济刺激主要包括，告诉医生不必要的手术可能引起的医疗事故诉讼。供给诱导需求Supplier-InducedDemand29信息不对称AsymmetricInformation信息问题InformationProblems患者——缺乏信息，也没有能力识别质量Patients—lackofinformationandinabilitytodiscernquality保险方——缺乏参保者的健康状况信息Insurers—lackofinformationaboutindividual’shealthbackground逆向选择Adverseselection假设有10个低风险的人和10个高风险的人，高风险的人预期的医疗保健费是1000美元，低风险的人预期的医疗保健费是100美元。医疗保险费的确定基于平均的预期医疗保健费，也就是550美元Supposethereare10lowriskpeopleand10highriskpeople,thehighriskpeople’sexpectedhealthcareexpenditurewillbe$1000,thelowrisk’swillbe$100.Thehealthinsurancepremiumisbasedonaverageexpectedexpenditure,whichis$550.

信息不对称AsymmetricInformation信息30逆向选择AdverseSelection保险公司无法区分风险高和风险低的人。保险费只反映了两类人的平均风险。因此高风险的人将购买保险，因为此时的保险费低于完全依照他们的风险确定的保险费。而低风险的人可能不会购买保险，因为此时的保险费高于完全依照他们的风险确定的保险费。Theinsurancecompanyisunabletodistinguishbetweenhighandlowrisks.Theinsurancepremiumonlyreflectstheaverageriskofthetwogroups.Then,thehighriskgroupwillpurchaseinsurancesinceapremiumbasedontheaverageriskislowerthanapremiumbasedsolelyontheirownrisk.Thelowriskindividualsmaynotpurchaseinsurancesinceapremiumbasedontheaveragewouldbegreaterthantheirownrisk-basedpremium.逆向选择AdverseSelection保险公司无法区分31逆向选择AdverseSelection逆向选择将会导致某些人购买医疗保险Adverseselectionwouldresultinabiasedsampleofthosethatpurchasehealthinsurance更多的高风险个人将购买保险Predominantly,morehighriskindividualswouldpurchaseinsurance“柠檬”法则TheLemonsPrinciple高风险的人驱逐低风险的人直至市场不存在Thebaddrivesoutthegooduntilnomarketisleft逆向选择AdverseSelection逆向选择将会导致32柠檬法则TheLemonsPrincipleAkerlof(1970)用信息不对称的观点分析二手车市场Akerlof(1970)usedtheideaofasymmetricinformationtoanalyzetheusedcarmarket二手车的质量千差万别Usedcarsavailableforsalevaryinquality对称不信息Asymmetricinformation卖者比买者更了解车子的质量Thesellersknowbetterthetruequalityoftheircarsthanthebuyers有9辆车供出售Thereare9carsforsale质量(Q)=0,¼,½,¾,1,1¼,1½,1¾,2卖者了解每辆车的质量Seller(owner)knowseachcar’squality买者只知道质量的分布Buyeronlyknowsthedistributionofquality柠檬法则TheLemonsPrincipleAkerl33柠檬法则TheLemonsPrinciple卖者的保留价值是$1000xQ

Sellerhasareservevalue=$1000xQ买者的保留价值是$1,500xQ

Buyerhasareservevalue=$1,500xQ雇佣一个拍卖人报价。拍卖人找到一个需求量等于供给量的价格就成交Anauctioneerishiredtocalloutprices.Salestakeplacewhentheauctioneerfindsapricethatmakesquantitydemandedequalquantitysupplied我们现在进行这个拍卖游戏Wedothesalesgametogetherinclass柠檬法则TheLemonsPrinciple卖者的保留34柠檬法则TheLemonsPrinciple如果信息对称，买者和卖者都不清楚具体的质量，他们只知道车子的平均质量，此时二手车市场能否存在？市场价格是多少？Ifinformationhadbeensymmetric,bothownersandbuyerswereuncertainofthequality,theyonlyknowtheaveragequalityofcars,thenisthereamarketfortheusedcars?Whatwouldbethemarketprice?柠檬法则TheLemonsPrinciple如果信息对35柠檬法则的应用：医疗保险ApplicationofTheLemonsPrinciple:HealthInsurance信息不对称Informationasymmetry潜在的参保者比医疗保险公司更了解自己将来可能的医疗保健支出Thepotentialinsuredpersonknowsmoreabouther(his)expectedhealthexpendituresinthecomingperiodthandoestheinsurancecompany.具体地讲Morespecifically参保者知道自己将来的医疗费用（类似于二手车的车主）Insuredknowsher(his)futureexpenditureexactly(similartotheownerofthecars)保险公司只了解所有参保者的医疗费用的分布（类似于买车的人）Insurancecompanyknowsonlythedistributionofexpendituresforallinsuredpersons(similartothebuyerofthecars)柠檬法则的应用：医疗保险ApplicationofThe36柠檬法则的应用：医疗保险ApplicationofTheLemonsPrinciple:HealthInsurance医疗保险市场有5个人Thereare5personsinhealthinsurancemarket预期的医疗费用＝0,¼,½,¾,1Expectedexpenditure=0,¼,½,¾,1平均医疗费用＝½Averageexpenditure=½我们再做一个游戏看医疗保险市场是否存在Wedothegameagaininclasstocheckifthereishealthinsurancemarket如果信息对称，参保者和保险公司都只知道风险的分布，那将会怎样？Ifinformationhadbeensymmetric,bothinsuredandinsurancecompanyonlyknowthedistributionofexpenditure,then?柠檬法则的应用：医疗保险ApplicationofThe37代理关系——委托代理问题AgencyRelationship—ThePrincipalAgentProblem代理关系Agencyrelationship委托方委托另一方，也就是代理方作出决定Aprincipaldelegatesdecision-makingauthoritytoanotherparty,theagent信息不对称和代理问题是相关的现象Asymmetricinformationandagencyarecloselyrelatedphenomena委托代理问题ThePrincipalAgentProblem怎样确定医生作出了最符合患者利益的决策Howtodeterminethephysicianisactinginthepatient’sbestinterests代理关系——委托代理问题AgencyRelationshi38供给诱导需求Supplier-InducedDemand供给诱导需求问题TheSupplier-InducedDemandproblem医生具有影响需求的利益驱动Thephysicianhasafinancialinteresttoinfluencethedemand.医生可以通过提供不准确的信息“创造”需求Thephysiciancan“create”thedemandbyprovidingthebiasedinformationtothepatient供给诱导需求问题源于信息不对称TheSIDproblemresultsfromasymmetricinformation患者和保险方都缺乏作出关于医疗方面的决策的必要信息Bothpatientsandinsurerslackthenecessaryinformationtomakemanymedical-relateddecision患者依赖于医生的建议和他们所提供的服务Thepatientdependsuponthephysicianforbothadviceandservice供给诱导需求Supplier-InducedDemand39供给诱导需求Supplier-InducedDemand传统的经济学模型Thetraditionaleconomicmodel传统的经济学模型假设医生是患者完美的代理人，可以推出其他条件不变，供给的增加将降低医生的收费，从而降低医生的收入。Thetraditionaleconomicmodel,whichassumesthephysicianisaperfectagentforthepatient,wouldpredictthatanincreaseinsupply,otherthingsbeingequal,wouldresultinadeclineinphysician’sfees,andconsequentlyphysicianincomes.现实的观察正好相反Theobservationinrealityisopposite需要更合理的理论解释医生的行为Needalternativetheorytostudyphysicianbehavior供给诱导需求Supplier-InducedDemand40S1S0D0E0E1供给诱导需求Supplier-InducedDemand传统的经济学模型Thetraditionaleconomicmodel供给量增加价格下降MQ0Q1P0P1PmS1S0D0E0E1供给诱导需求Supplier-Indu41供给诱导需求Supplier-InducedDemand供给诱导需求的价格刚性模型ThepricerigiditymodelofSID为什么竞争的市场会出现诱导需求？一种解释是假设医疗价格倾向于刚性Oneapproachthatcanexplaindemandinducementwithinthecontextofacompetitivemarketmodelistoarguethatpricestendtoberigid随着供给增加，为了保持固定的价格，医生具有增加需求的激励Assupplyincreases,inordertofixtheprice,thephysicianhasincentivetoinducedemand但是这个理论只能解释为何价格没有下降，但不能解释为何价格上升Butthismodelcanonlyexplainwhypricedoesn’tgodownandcan’texplainwhypricegoesup供给诱导需求Supplier-InducedDemand42D1供给诱导需求Supplier-InducedDemandSID的价格刚性模型ThepricerigiditymodelofSID供给量增加价格不变S1E0MQ0Q2P0PmS0D0E2D1供给诱导需求Supplier-InducedDema43供给诱导需求Supplier-InducedDemandSID的目标收入模型ThetargetincomemodelofSID尽管医生的供给快速增加，医疗价格仍然上升Thepriceofhealthcareincreasesdespiterapidincreaseinphysiciansupply目标收入模型用以解释医生收费的快速上升Thetargetincomemodelisusedtoexplaintherapidincreaseinphysicianfees.在目标收入假设下，医生供给的增加导致收费的上升以保证目标收入，或者医生将诱导患者的需求以保证目标收入Underthetargetincomehypothesis,increaseinsupplyofphysiciansleadtohigherfeesinorderforearningtobemaintained,orphysicianwillinducedemandtomaintainthetargetincome供给诱导需求Supplier-InducedDemand44供给诱导需求Supplier-InducedDemandSID的目标收入模型ThetargetincomemodelofSID供给量增加价格上升D1S1E0S0D0E2MQ0Q2P0PmP1供给诱导需求Supplier-InducedDemand45供给诱导需求Supplier-InducedDemandSID的目标收入模型ThetargetincomemodelofSID目标收入假设的主要证据是医生/人口比率和医生收费呈正相关Themajorevidencefortargetincomehypothesisisthatphysician/populationratiosarepositivelyrelatedtophysicianfees医生诱导需求的范围和价格水平取决于医生期望的收入目标Theextentofthedemandthephysiciancancreateandthepricethatwillbeestablishedarebaseduponwhattargetincomethephysiciandesires目标收入水平取决于当地的收入水平，尤其是其他医生和专业人士的收入水平Thetargetincomeisdeterminedbythelocalincomedistribution,particularlywithrespecttotheincomeofother