博弈论与实验经济学2.docx

博弈论与实验经济学2.docx

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博弈论与实验经济学2

8/10/05

Chapter10WhyEnvironmentalProblemsAreEasytoArise,HardtoFix

Summary

10.1Introduction

10.2TheFishermen’sDilemma（TheGenesisoftheProblem）

10.3TheOriginalPrisoners’Dilemma（WithItsSpillovertotheRemedy）

10.3.1TheDistrictAttorney’sIncentivesandtheLargerSociety

10.4TheWoburnToxicsCase（ACaseStudy）

10.4.1TheHarm

10.4.2DecidingonaLawsuit

10.4.3ThePlaintiffs’Tasks

10.4.4TheStrategies

10.4.5Preparations

10.4.6TheTrial

10.5NegligenceandStrictLiability

10.5.1Unforseeability

10.5.2StrictLiability

10.5.3TheLinkbetweenStrictLiabilityandBrier’sScoringRule

10.6Summary

AnalyticQuestion

DiscussionQuestions

10.7Appendix:

ABriefHistoryoftheConceptofExternality

FiguresandTables

Figure10.1Fishermen’sDilemma

Figure10.2TheOriginalPrisoners’Dilemma

Figure10.3ExternalityinTortLaw

Figure10.4Externality

Figure10.5Schlichtmann’sProbabilityAssessment

Figure10.6ThePreponderanceoftheEvidenceasaLegalStandard

Figure10.7TheEarliestDateofContamination,byaPreponderanceoftheEvidence

Table10.1Profit,DependingonxandPossibleLiabilityof$600x

Figure10.8TheFirm’sProbabilitiesandDecisionConsequences

Figure10.9TheParabolaofExpectedProfit

Figure10.10TheChemicalFirm’sDecisionFunction

Table10.2TheBrierScoringRule

Figure10.11TheWeatherForecaster’sDecisionFunction

Figure10.12TheChemicalFirm’sDecisionFunctionfortheLessToxicChemical

Chapter10WhyEnvironmentalProblemsAreEasytoArise,HardtoFix

Ifmenwereangels,nogovernmentwouldbenecessary.

--JamesMadison（TheFederalist,Feb.6,1788）

Thewaterhadnevertastedright,itneverlookedright,anditneversmelledright.

--AnneAnderson（citedfromACivilAction,p.21.

Thetruth?

Truthisatthebottomofabottomlesspit.

--JeromeFacher（citedfromACivilAction,p.340.

10.1Introduction

Athemeinourinquirysofaristhatthecombinationofindividualself-interestandexternalityisaprimarysourceofenvironmentalproblems.Boththegenesisandtheeffectsofexternalitiesarefurthershapedbytheconflictinginterestsamongdifferentpeople,uncertainty,anddifficultiesofvaluationsocommoninenvironmentalproblems.Individualselfinterestofcoursedoesnotalwaysleadtoexternalitiesandenvironmentalproblems.WesawinChapter6anexampleofawell-functioningmarketwithoutexternalitiesandenvironmentalproblems（andthenwesawinChapter7amarketfailurewithexternalitiesandenvironmentalproblems）.

Inthischapterwebeginwithaclassicexampleofselfinterestandexternality,andthenshiftourfocustoattemptsofremedy.Wewillfindthatthesamecharacteristicsthatleadtoenvironmentalproblemsinthefirstplacemakethemhardtoremedyinthesecondplace.

10.2TheFishermen’sDilemma（TheGenesisoftheProblem）

Webeginwithaparticularlysimpleexampleofafishery.Considertheexampleoftwofishermen,AandB,andFigure10.1below.

IfbothAandBfishalittle,bothgetalargecatch（theupperleftrectangle）.ThelowleveloffishingeffortofbothAandBavoidsover-fishing,allowingforthefishtoreproduceeffectively,leadingtolargeharvestsforbothfishermen.

IfbothAandBfishalot,bothgetasmallcatch（lowerright）.Theintensivefishingleadstoover-fishing,depletingthefishery’sproductivityandcausingasmallharvestforbothfishermen.Intheexternalityeachfishermanharmstheotherbydepletingtheresourcebase.

IfAfishesalotandBfishesalittle,AgetsanextralargecatchandBgetsanextrasmallone（upperright）.Thefisheryisalittledepleted.AgetsanextralargecatchbecauseAfishesalotintheonlypartiallydepletedfishery;BgetsanextrasmallcatchbecauseBfishesalittleinthepartiallydepletedfishery.

IfBfishesalotandAfishesalittle,BgetsanextralargecatchandAgetsanextrasmallcatch（lowerleft）.Thefisheryisalittledepleted.BgetsanextralargecatchbecauseBfishesalotintheonlypartiallydepletedfishery;AgetsanextrasmallcatchbecauseAfishesalittleinthepartiallydepletedfishery.

Figure10.1

IfAandBcouldcooperateandcoordinate,theobviousthingtodoisforbothtofishalittle.Butinourexample,communicationishardandthefishermendon’tcooperate.Perhapstheyspeakdifferentlanguagesorcomefromdifferentcontinents,asisthecaseinmanyoftheworld’sfisheries.Wheneachfishermandoesthebesthecanforhimselfthereisanincentiveforeachpersontofishalot,eventhoughdoingsoleadstoabadsocialoutcome.Here’sthewaytheincentiveworks.FishermanAreasons:

“SupposeBfishesalittle.ThenifIfishalittleIgetalargecatch（upperleft）.ButifIfishalotIgetanextralargecatch（upperright）.SowhenBfishesalittleIambetterofffishingalot.

“SupposeBfishesalot.ThenifIfishalittleIgetanextrasmallcatch（lowerleft）.IfIfishalotIgetasmallcatch（lowerright）.SowhenBfishesalotIambetterofffishingalot.

“WhateverBdoes,Iambetterofffishingalot.IguessIwillfishalot.”

Breasonsinasimilarway,andtogethertheyendupdepletingtheresourceandhurtingthemselves.AhasadominantstrategyoffishingalotbecausefishingalotishisbeststrategynomatterwhatBdoes.BalsohasadominantstrategyoffishingalotbecausefishingalotishisbeststrategynomatterwhatAdoes.Thestrategypair（Afishesalot,Bfishesalot）iscalledanequilibriumindominantstrategies.Theequilibriumpredictsthatbothfishermenwillendupwithasmallcatch,whentheycouldbothhavealargecatch.Insummary,theexamplesaysthat“self-interestinthepresenceofexternalitiescanleadtoinefficiency,”inthiscasetheinefficiencyofover-fishing.It’sthesameideaasinGordon’sfisheryproblem,butwithasimplermodel.

Youmayhaverecognizedtheexampleisaprisoners’dilemma,appliedtoanenvironmentalproblem.Initsvariousversions,theprisoners’dilemmahasintriguedgametheoristsandeconomistsforthelasthalf-centurybecauseitsodirectlyillustratestheideathatwhatisgoodfortheindividualcanbebadforsociety（thesocietyofthetwofishermenendupwiththeinefficient,depletedfishery）.Inthiswaytheprisoners’dilemmaparallelsthehawk-dovegame,whichillustratestheideathatwhatisgoodfortheindividualfitnessofanindividualbirdcanbeharmfultothespeciesasawhole.Andjustasthehawk-dovegameisanelegantlysimplemodelthathelpedchangethewaybiologiststhinkaboutevolution,theprisoners’dilemmaisanelegantlysimplemodelthathelpedchangethewayeconomiststhinkaboutenvironmentalproblems.

MaynardSmith’shawk-dovegameprovidesasimpleandclearalternativetotheolderviewthatadaptationsbenefitingindividualsautomaticallybenefitthespecies（Chapter3）.Inaparallelwaytheprisoner’sdilemmaprovidesasimpleandclearalternativetotheolderviewofAdamSmith’sinvisiblehandautomaticallyleadsindividualinteresttothepublicinterest（Chapter6）.

Thefishermen’sdilemma,ourenvironmentalversionoftheprisoners’dilemma,bybeingsimple,isstylizedandmuchisleftout.Narrowself-interestisnottheonlymotivator.IfAweretofishalotandBtofishalittle,wouldn’ttherebemoralpressureonAtoconserveandnotinjurethefisheryandB?

Thereareofcourseother-directedvaluesofcooperation,reciprocity,andaltruism,whichwewillstudyinthenextchapter.Butwithmanyoftheworld’sfisheriesindecline,thesevaluesareofteninsufficienttoovercomeself-interestinthepresenceofexternalities.JamesMadison,anarchitectoftheU.S.ConstitutionandfourthPresident,putthematter,“Ifmenwereangels,nogovernmentwouldbenecessary.”SinceMadisonthoughtgovernmentwasnecessary,hisobviousinferenceisthatmenaren’tangels.

Butifmenaren’tangels,doestheprisoners’dilemma,simpleandstylizedasitis,haveanythingtosayaboutthedifficultiesofnon-angelsinfashioningremediesingovernmentagencies?

Toaddressthisquestion,wegobacktotheoriginalversionoftheprisoners’dilemma.

10.3TheOriginalPrisoners’Dilemma（WithItsSpillovertotheRemedy）

Thereisastory（probablyincorrect）thatscholarlyinterestintheprisoners’dilemmabeganwhenapioneergametheoristwassittinginabarbershop.Whilecuttinghiscustomer’shair,thebarbermadeconversationbyaskinghiscustomerwhatgametheorywas.Thetheoristgaveafewwordsofexplanation,andthebarberrespondedbyasking“haveyouheardthisone?

”

“TherearetwoprisonersAandB,justcaughtandsuspectsforacrime（Figure10.2）.Thereissomeevidencebutpossiblynotenoughtogetaconvictionincourt.Thedistrictattorneyinchargeofthecaseputstheprisonersintoseparatecellswheretheycannotcommunicatewitheachother.ThedistrictattorneygoestothecellholdingAandtellshim:

“Ifyou（A）knowwhatisgoodforyouandyoucooperatewithmebypleadingguilty,thingswillgowellforyou.HowmuchbetterdependsonB.IfBalsocooperates,Iwillseekareasonablesentenceforthecrime,6yearsforeachofyou（lowerright）.IfBremainssilent,Iwillthrowthebookathim,butIwillrewardyouwithanextralightsentenceofjustayear（upperright）.

Figure10.2

“Ifyou（A）don’tcooperatewithme,thingswillgohardforyou.JusthowharddependsonwhatBdoes.IfBtestifiesagainstyou,andyoukeepsilent,Iwillusehisevidencetoputyouinprisonfor10years（lowerleft）.Ifhekeepssilent,Istillhaveenoughevidencetoputyouinprisonfor2years（upperleft）.IfyourefusetocooperatewithmeIwillt