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1、信息不对称 Asymmetric Information(卫生经济学)Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望逆向选择 Adverse Selectionn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。The insurance company is unable to dist
2、inguish between high and low risks.The insurance premium only reflects the average risk of the two groups.Then,the high risk group will purchase insurance since a premium based on the average risk is lower than a premium based solely on their own risk.The low risk individuals may not purchase insura
3、nce since a premium based on the average would be greater than their own risk-based premium.逆向选择 Adverse Selectionn逆向选择将会导致某些人购买医疗保险Adverse selection would result in a biased sample of those that purchase health insurancen更多的高风险个人将购买保险 Predominantly,more high risk individuals would purchase insuranc
4、en“柠檬”法则 The Lemons Principlen高风险的人驱逐低风险的人直至市场不存在 The bad drives out the good until no market is left柠檬法则 The Lemons PrinciplenAkerlof(1970)用信息不对称的观点分析二手车市场 Akerlof(1970)used the idea of asymmetric information to analyze the used car marketn二手车的质量千差万别 Used cars available for sale vary in qualityn对称不
5、信息 Asymmetric informationn卖者比买者更了解车子的质量 The sellers know better the true quality of their cars than the buyersn有9辆车供出售 There are 9 cars for salen质量(Q)=0,1,1,1,1,2n卖者了解每辆车的质量 Seller(owner)knows each cars qualityn买者只知道质量的分布 Buyer only knows the distribution of quality 柠檬法则 The Lemons Principlen卖者的保留价值
6、是$1000 xQ Seller has a reserve value=$1000 xQn买者的保留价值是$1,500 xQ Buyer has a reserve value=$1,500 xQn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 An auctioneer is hired to call out prices.Sales take place when the auctioneer finds a price that makes quantity demanded equal quantity suppliedn我们现在进行这个拍卖游戏 We do the
7、 sales game together in class柠檬法则 The Lemons Principlen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？If information had been symmetric,both owners and buyers were uncertain of the quality,they only know the average quality of cars,then is there a market for the used cars?What would be the m
8、arket price?柠檬法则的应用：医疗保险Application of The Lemons Principle:Health Insurancen信息不对称 Information asymmetryn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 The potential insured person knows more about her(his)expected health expenditures in the coming period than does the insurance company.n具体地讲 More specificallyn参保者知道
9、自己将来的医疗费用（类似于二手车的车主）Insured knows her(his)future expenditure exactly(similar to the owner of the cars)n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）Insurance company knows only the distribution of expenditures for all insured persons(similar to the buyer of the cars)柠檬法则的应用：医疗保险Application of The Lemons Principle:H
10、ealth Insurancen医疗保险市场有5个人 There are 5 persons in health insurance marketn预期的医疗费用0,1 Expected expenditure=0,1n平均医疗费用 Average expenditure=n我们再做一个游戏看医疗保险市场是否存在 We do the game again in class to check if there is health insurance marketn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？If information had been symmetric,bo
11、th insured and insurance company only know the distribution of expenditure,then?代理关系委托代理问题Agency RelationshipThe Principal Agent Problemn代理关系 Agency relationshipn委托方委托另一方，也就是代理方作出决定 A principal delegates decision-making authority to another party,the agentn信息不对称和代理问题是相关的现象 Asymmetric information and
12、 agency are closely related phenomenan委托代理问题 The Principal Agent Problemn怎样确定医生作出了最符合患者利益的决策 How to determine the physician is acting in the patients best interests供给诱导需求 Supplier-Induced Demandn供给诱导需求问题 The Supplier-Induced Demand problemn医生具有影响需求的利益驱动 The physician has a financial interest to infl
13、uence the demand.n医生可以通过提供不准确的信息“创造”需求 The physician can“create”the demand by providing the biased information to the patientn供给诱导需求问题源于信息不对称 The SID problem results from asymmetric informationn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 Both patients and insurers lack the necessary information to make many medical-r
14、elated decisionn患者依赖于医生的建议和他们所提供的服务 The patient depends upon the physician for both advice and service供给诱导需求 Supplier-Induced Demandn传统的经济学模型 The traditional economic modeln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。The traditional economic model,which assumes the physician is a perfec
15、t agent for the patient,would predict that an increase in supply,other things being equal,would result in a decline in physicians fees,and consequently physician incomes.n现实的观察正好相反 The observation in reality is oppositen需要更合理的理论解释医生的行为 Need alternative theory to study physician behaviorS1S0D0E0E1供给诱
16、导需求 Supplier-Induced Demandn传统的经济学模型 The traditional economic modeln供给量增加n价格下降MQ0Q1P0P1Pm供给诱导需求 Supplier-Induced Demandn供给诱导需求的价格刚性模型 The price rigidity model of SIDn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 One approach that can explain demand inducement within the context of a competitive market model is t
17、o argue that prices tend to be rigidn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 As supply increases,in order to fix the price,the physician has incentive to induce demandn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 But this model can only explain why price doesnt go down and cant explain why price goes upD1供给诱导需求 Supplier-Ind
18、uced DemandnSID的价格刚性模型 The price rigidity model of SIDn供给量增加n价格不变S1E0MQ0Q2P0PmS0D0E2供给诱导需求 Supplier-Induced DemandnSID的目标收入模型 The target income model of SIDn尽管医生的供给快速增加，医疗价格仍然上升 The price of health care increases despite rapid increase in physician supplyn目标收入模型用以解释医生收费的快速上升 The target income model
19、is used to explain the rapid increase in physician fees.n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 Under the target income hypothesis,increase in supply of physicians lead to higher fees in order for earning to be maintained,or physician will induce demand to maintain the target income供给诱导需
20、求 Supplier-Induced DemandnSID的目标收入模型 The target income model of SIDn供给量增加n价格上升D1S1E0S0D0E2MQ0Q2P0PmP1供给诱导需求 Supplier-Induced DemandnSID的目标收入模型 The target income model of SIDn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 The major evidence for target income hypothesis is that physician/population ratios are positivel
21、y related to physician feesn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 The extent of the demand the physician can create and the price that will be established are based upon what target income the physician desiresn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 The target income is determined by the local income distribution,
22、particularly with respect to the income of other physicians and professionals供给诱导需求 Supplier-Induced DemandnSID的利润最大化模型MQ1Q2P2PmP1MR2D1MC1MR1D2MC2供给诱导需求 Supplier-Induced DemandnRoemer&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？(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
23、，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-Induced DemandS1S2S3S0Q0Q1Q2Q3DMP0Pm解释一解释一(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-Induced DemandD0S0D1S1MQ0Q1Pm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，
24、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：解释二解释二MQ1Q2P1P2Pm供给诱导需求 Supplier-Induced Demand医生通过收治患者入院来提高效益。解释三解释三供给诱导需求 Supplier-Induced Demand还有其他解释吗？供给诱导需求 Supplier-Induced Demandn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。n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
25、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-Induced Demand供给诱导需求 Supplier-Induced Demand供给诱导需求 Supplier-Induced Demandn供给诱导需求的识别问题 The identification problem of SIDn实证研究中，诱导需求的影响无法用计量方法识别 In
26、the empirical work,the SID effect cannot be econometrically identifiedn很难区分患者的需求和医生诱导的需求 It is hard to distinguish between patients demand and physicians induced demand供给诱导需求 Supplier-Induced Demandn供给诱导需求的成本 The costs of SIDn时间成本 Time costn声誉下降 Reputation lossn“心理精神”成本“psychic”cost供给诱导需求 Supplier-Induced Demandn避免医生创造需求的方法：n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。n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。n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。