信息不对称AsymmetricInformation(卫生经济学)

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.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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柠檬法则TheLemonsPrincipleAkerlof(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TheLemonsPrinciple卖者的保留价值是$1000xQSellerhasareservevalue=$1000xQ买者的保留价值是$1,500xQBuyerhasareservevalue=$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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?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-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NeedalternativetheorytostudyphysicianbehaviorS1S0D0E0E1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MQ0Q1P0P1Pm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’texplainwhypricegoesupD1供给诱导需求Supplier-InducedDemandSID的价格刚性模型Thepricerigiditymo