柠檬的市场质量的不确定性和市场机制外文翻译.docx

柠檬的市场质量的不确定性和市场机制外文翻译.docx

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柠檬的市场质量的不确定性和市场机制外文翻译

外文翻译

原文

Themarketfor"lemons":

qualityuncertaintyandthemarketmechanism

MaterialSource:

TheQuarterlyJournalofEconomics,1970Author:

GEORGEA.AKERLOF

I.INTRODUCTION

Thispaperrelatesqualityanduncertainty.Theexistenceofgoodsofmanygradesposesinterestingandimportantproblemsforthetheoryofmarkets.Ontheonehand,theinteractionofqualitydifferencesanduncertaintymayexplainimportantinstitutionsofthelabormarket.Ontheotherhand,thispaperpresentsastrugglingattempttogivestructuretothestatement:

"Businessinunderdevelopedcountriesisdifficult";inparticular,astructureisgivenfordeterminingtheeconomiccostsofdishonesty.Additionalapplicationsofthetheoryincludecommentsonthestructureofmoneymarkets,onthenotionof"insurability,"ontheliquidityofdurables,andonbrand-namegoods.

Therearemanymarketsinwhichbuyersusesomemarketstatistictojudgethequalityofprospectivepurchases.Inthiscasethereisincentiveforsellerstomarketpoorqualitymerchandise,sincethereturnsforgoodqualityaccruemainlytotheentiregroupwhosestatisticisaffectedratherthantotheindividualseller.Asaresulttheretendstobeareductionintheaveragequalityofgoodsandalsointhesizeofthemarket.Itshouldalsobeperceivedthatinthesemarketssocialandprivatereturnsdiffer,andtherefore,insomecases,governmentalinterventionmayincreasethewelfareofallparties.Orprivateinstitutionsmayarisetotakeadvantageofthepotentialincreasesinwelfarewhichcanaccruetoallparties.Bynature,however,theseinstitutionsarenonatomistic,andthereforeconcentrationsofpowerwithillconsequencesoftheirowncandevelop.

Theautomobilemarketisusedasafingerexercisetoillustrateanddevelopthesethoughts.Itshouldbeemphasizedthatthismarketischosenforitsconcretenessandeaseinunderstandingratherthanforitsimportanceorrealism.

II.THEMODELWITHAUTOMOBILESASANEXAMPLE

A.TheAutomobilesMarket

Theexampleofusedcarscapturestheessenceoftheproblem.Fromtimetotimeonehearseithermentionoforsurpriseatthelargepricedifferencebetweennewcarsandthosewhichhavejustlefttheshowroom.Theusuallunchtablejustificationforthisphenomenonthepurejoyofowninga"new"car.Weofferadifferentexplanation.Suppose（forthesakeofclarityratherthanreality）thattherearejustfourkindsofcars.Therearenewcarsandusedcars.Therearegoodcarsandbadcars（whichinAmericaareknownas"lemons"）.Anewcarmaybeagoodcaroralemon,andofcoursethesameistrueofusedcars.

Theindividualsinthismarketbuyanewautomobilewithoutknowingwhetherthecartheybuywillbegoodoralemon.Buttheydoknowthatwithprobabilityqitisagoodcarandwithprobability（1-q）itisalemon;byassumption,qistheproportionofgoodcarsproducedand（1-q）istheproportionoflemons.

Afterowningaspecificcar,however,foralengthoftime,thecarownercanformagoodideaofthequalityofthismachine;i.e.,theownerassignsanewprobabilitytotheeventthathiscarisalemon.Thisestimateismoreaccuratethantheoriginalestimate.Anasymmetryinavailableinformationhasdeveloped:

forthesellersnowhavemoreknowledgeaboutthequalityofacarthanthebuyers.Butgoodcarsandbadcarsmuststillsellatthesamepricesinceitisimpossibleforabuyertotellthedifferencebetweenagoodcarandabadcar.Itisapparentthatausedcarcannothavethesamevaluationasanewcar.ifitdidhavethesamevaluation,itwouldclearlybeadvantageoustotradealemonatthepriceofnewcar,andbuyanothernewcar,atahigherprobabilityqofbeinggoodandalowerprobabilityofbeingbad.Thustheownerofagoodmachinemustbelockedin.Notonlyisittruethathecannotreceivethetruevalueofhiscar,buthecannotevenobtaintheexpectedvalueofanewcar.

Gresham'slawhasmadeamodifiedreappearance.Formostcarstradedwillbethe"lemons,"andgoodcarsmaynotbetradedatall.The"bad"carstendtodriveoutthegood（inmuchthesamewaythatbadmoneydrivesoutthegood）.ButtheanalogywithGresham'slawisnotquitecomplete:

badcarsdriveoutthegoodbecausetheysellatthesamepriceasgoodcars;similarly,badmoneydrivesoutgoodbecausetheexchangerateiseven.Butthebadcarssellatthesamepriceasgoodcarssinceitisimpossibleforabuyertotellthedifferencebetweenagoodandabadcar;onlythesellerknows.InGresham'slaw,however,presumablybothbuyerandsellercantellthedifferencebetweengoodandbadmoney.Sotheanalogyisinstructive,butnotcomplete.

B.AsymmetricalInformation

Ithasbeenseenthatthegoodcarsmaybedrivenoutofthemarketbythelemons.Butinamorecontinuouscasewithdifferentgradesofgoods,evenworsepathologiescanexist.Foritisquitepossibletohavethebaddrivingoutthenot-so-baddrivingoutthemediumdrivingoutthenot-so-gooddrivingoutthegoodinsuchasequenceofeventsthatnomarketexistsatall.Onecanassumethatthedemandforusedautomobilesdependsmoststronglyupontwovariablesthepriceoftheautomobilepandtheaveragequalityofusedcarstraded,a,orQ=D（p,A）.Boththesupplyofusedcarsandalsotheaveragequalitypwilldependupontheprice,orp=j（p）andS=S（p）.Andinequilibriumthesupplymustequalthedemandforthegivenaveragequality,orS（p）=D（p,p（p））.Asthepricefalls,normallythequalitywillalsofall.Anditisquitepossiblethatnogoodswillbetradedatanypricelevel.

Suchanexamplecanbederivedfromutilitytheory.Assumethattherearejusttwogroupsoftraders:

groupsoneandtwo.Givegrouponeautilityfunction

n

U1=M+∑Xi

i=1

whereMistheconsumptionofgoodsotherthanautomobiles,X1isthequalityoftheI.T.Hautomobile,andNisthenumberofautomobiles.Similarly,let

n

U2=M+∑X3/2Xi

i=1

whereM,X1,andNaredefinedasbefore.Threecommentsshouldbemadeabouttheseutilityfunctions:

（1）withoutlinearutility（saywithlogarithmicutility）onegetsneedlesslymiredinalgebraiccomplication.

（2）Theuseoflinearutilityallowsafocusontheeffectsofasymmetryofinformation;withaconcaveutilityfunctionwewouldhavetodealjointlywiththeusualriskvarianceeffectsofuncertaintyandthespecialeffectswewishtodiscusshere.（3）U1andU2havetheoddcharacteristicthattheadditionofasecondcar,orindeedaKTHcar,addsthesameamountofutilityasthefirst.Againrealismissacrificedtoavoidadiversionfromtheproperfocus.

Tocontinue,itisassumed

（1）thatbothtypeonetradersandtypetwotradersareVonNeumannMorgensternmaximizersofexpectedutility;

（2）thatgrouponehasNcarswithuniformlydistributedqualityx,0

Denotetheincome（includingthatderivedfromthesaleofautomobiles）ofalltypeonetradersasY1andtheincomeofalltypetwotradersasY2.Thedemandforusedcarswillbethesumofthedemandsbybothgroups.Whenoneignoresindivisibility,thedemandforautomobilesbytypeonetraderswillbe

D1=Y1/pμ/p>l

D1=Oμ/p

Andthesupplyofcarsofferedbytypeonetradersis

S2=PN/2p≤2

withaveragequality

i=p/2.

（Toderive

（1）and

（2）,theuniformdistributionofautomobilequalityisused.）

Similarlythedemandoftypetwotradersis

D2=Y2/P3μ/2>p

D2=03μ/2

and

S2=0.

ThustotaldemandD（p,μ）is

D（p,μ）=（Y2+Y1）/Pifp<μ

D（p,μ）=Y2/pifμ

D（p,μ）=0ifp>3μ/2.

However,withpricep,averagequalityisp/2andthereforeatnopricewillanytradetakeplaceatall:

inspiteofthefactthatatanygivenpricebetween0and3therearetradersoftypeonewhoarewillingtoselltheirautomobilesatapricewhichtradersoftypetwoarewillingtopay.

C.SymmetricInformationTheforegoingiscontrastedwiththecaseofsymmetricinformation.Supposethatthequalityofallcarsisuniformlydistributed,O

Supply

S（p）=Np>1

S（p）=Op<1.

Andthedemandcurvesare

D（p）=（Y2+May）/Pp<1

D（p）=（Y2/p）l

D（p）=0p>3/2.

Inequilibrium

p=1ifY2

P=Y2/Nif2Y2/3

p=3/2ifN<2Y2/3.

IfNY2,inwhichcasetheincomeoftypetwotradersisinsufficienttobuyallNautomobiles,thereisagaininutilityofY2/2units.

Finally,itshouldbementionedthatinthisexample,iftradersofgroupsoneandtwohavethesameprobabilisticestimatesaboutthequalityofindividualautomobilesthoughtheseestimatesmayvaryfromautomobiletoautomobile（3）,（4）,and（5）willstilldescribeequilibriumwithoneslightchange:

pwillthenrepresenttheexpectedpriceofonequalityunit.

III.EXAMPLESANDAPPLICATIONS

A.Insurance

Itisawell-knownfactthatpeopleover65havegreatdifficultyinbuyingmedicalinsurance.Thenaturalquestionarises:

whydoesn'tthepricerisetomatchtherisk?

Ouransweristhatasthepricelevelrisesthepeoplewhoinsurethemselveswillbethosewhoareincreasinglycertainthattheywillneedtheinsurance;forerrorinmedicalcheck-ups,doctors'sympathywitholderpatients,andsoonmakeitmucheasierfortheapplicanttoassesstherisksinvolvedthantheinsurancecompany.Theresultisthattheaveragemedicalconditionofinsuranceapplicantsdeterioratesasthepricelevelriseswiththeresultthatnoinsurancesalesmaytakeplaceatanyprice.'Thisisstrictlyanalogoustoourauto