范里安微观第36章讲义.ppt

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1、ChapterThirty-SixAsymmetricInformation不对称信息InformationinCompetitiveMarketsInpurelycompetitivemarketsallagentsarefullyinformedabouttradedcommoditiesandotheraspectsofthemarket.Whataboutmarketsformedicalservices,orinsurance,orusedcars?AsymmetricInformationinMarketsAdoctorknowsmoreaboutmedicalservicest

2、handoesthebuyer.Aninsurancebuyerknowsmoreabouthisriskinessthandoestheseller.Ausedcar’sownerknowsmoreaboutitthandoesapotentialbuyer.AsymmetricInformationinMarketsMarketswithonesideortheotherimperfectlyinformedaremarketswithimperfectinformation(不完全信息).Imperfectlyinformedmarketswithonesidebetterinform

3、edthantheotheraremarketswithasymmetricinformation(不对称信息).AsymmetricInformationinMarketsInwhatwayscanasymmetricinformationaffectthefunctioningofamarket?Fourapplicationswillbeconsidered:adverseselection(逆向选择)signaling(信号传递)moralhazard(道德风险)incentivescontracting.AdverseSelectionConsiderausedcarmarket.

4、Twotypesofcars;“lemons”and“peaches”.Eachlemonsellerwillaccept$1,000;abuyerwillpayatmost$1,200.Eachpeachsellerwillaccept$2,000;abuyerwillpayatmost$2,400.AdverseSelectionIfeverybuyercantellapeachfromalemon,thenlemonssellforbetween$1,000and$1,200,andpeachessellforbetween$2,000and$2,400.Gains-to-tradea

5、regeneratedwhenbuyersarewellinformed.AdverseSelectionSupposenobuyercantellapeachfromalemonbeforebuying.Whatisthemostabuyerwillpayforanycar?AdverseSelectionLetqbethefractionofpeaches.1-qisthefractionoflemons.ExpectedvaluetoabuyerofanycarisatmostAdverseSelectionSupposeEV>$2000.Everysellercannegotiate

6、apricebetween$2000and$EV(nomatterifthecarisalemonorapeach).Allsellersgainfrombeinginthemarket.AdverseSelectionSupposeEV<$2000.Apeachsellercannotnegotiateapriceabove$2000andwillexitthemarket.Soallbuyersknowthatremainingsellersownlemonsonly.Buyerswillpayatmost$1200andonlylemonsaresold.AdverseSelectio

7、nHence“toomany”lemons“crowdout”thepeachesfromthemarket.Gains-to-tradearereducedsincenopeachesaretraded.Thepresenceofthelemonsinflictsanexternalcostonbuyersandpeachowners.AdverseSelectionHowmanylemonscanbein