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1、CHAPTER3GlobalGames:TheoryandApplicationsStephenMorrisandHyunSongShin1.INTRODUCTIONManyeconomicproblemsarenaturallymodeledasagameofincompleteinfor-mation,whereaplayer’spayoffdependsonhisownaction,theactionsofothers,andsomeunknowneconomicfundamentals.Forexample,many
2、accountsofcurrencyattacks,bankruns,andliquiditycrisesgiveacentralroletoplayers’uncertaintyaboutotherplayers’actions.Becauseotherplayers’actionsinsuchsituationsaremotivatedbytheirbeliefs,thedecisionmakermusttakeaccountofthebeliefsheldbyotherplayers.Weknowfromtheclas
3、siccontributionofHarsanyi(1967–1968)thatrationalbehaviorinsuchenvironmentsnotonlydependsoneconomicagents’beliefsabouteconomicfundamentals,butalsodependsonbeliefsofhigher-order–i.e.,players’beliefsaboutotherplayers’beliefs,players’beliefsaboutotherplayers’beliefsabo
4、utotherplayers’beliefs,andsoon.Indeed,MertensandZamir(1985)haveshownhowonecangiveacompletedescriptionofthe“type”ofaplayerinanincompleteinformationgameintermsofafullhierarchyofbeliefsatalllevels.Inprinciple,optimalstrategicbehaviorshouldbeanalyzedinthespaceofallposs
5、ibleinfinitehierarchiesofbeliefs;however,suchanalysisishighlycomplexforplayersandanalystsalikeandislikelytoproveintractableingeneral.Itisthereforeusefultoidentifystrategicenvironmentswithincompleteinformationthatarerichenoughtocapturetheimportantroleofhigher-orderbe
6、liefsineconomicsettings,butsimpleenoughtoallowtractableanalysis.Globalgames,firststudiedbyCarlssonandvanDamme(1993a),representonesuchenvironment.Uncertaineconomicfundamentalsaresummarizedbyastateθandeachplayerobservesadifferentsignalofthestatewithasmallamountofnoise
7、.Assumingthatthenoisetechnologyiscommonknowledgeamongtheplayers,eachplayer’ssignalgeneratesbeliefsaboutfundamentals,beliefsaboutotherplayers’beliefsaboutfundamentals,andsoon.Ourpurposeinthispaperistodescribehowsuchmodelswork,howglobalgamereasoningcanbeappliedtoecon
8、omicproblems,andhowthisanalysisrelatestomoregeneralanalysisofhigher-orderbeliefsinstrategicsettings.CambridgeCollectionsOnline©CambridgeUniversit