范里安微观经济学现代观点原版讲义.ppt

ChapterOne TheMarket TheTheoryofEconomicsdoesnotfurnishabodyofsettledconclusionsimmediatelyapplicabletopolicy Itisamethodratherthanadoctrine anapparatusofthemind atechniqueofthinkingwhichhelpsitspossessortodrawcorrectconclusions JohnMaynardKeynes EconomicModeling Whatcauseswhatineconomicsystems Atwhatlevelofdetailshallwemodelaneconomicphenomenon Whichvariablesaredeterminedoutsidethemodel exogenous andwhicharetobedeterminedbythemodel endogenous ModelingtheApartmentMarket Howareapartmentrentsdetermined Supposeapartmentsarecloseordistant butotherwiseidenticaldistantapartmentsrentsareexogenousandknownmanypotentialrentersandlandlords ModelingtheApartmentMarket Whowillrentcloseapartments Atwhatprice Willtheallocationofapartmentsbedesirableinanysense Howcanweconstructaninsightfulmodeltoanswerthesequestions EconomicModelingAssumptions Twobasicpostulates RationalChoice Eachpersontriestochoosethebestalternativeavailabletohimorher Equilibrium Marketpriceadjustsuntilquantitydemandedequalsquantitysupplied ModelingApartmentDemand Demand Supposethemostanyonepersoniswillingtopaytorentacloseapartmentis 500 month Thenp 500 QD 1 Supposethepricehastodropto 490beforea2ndpersonwouldrent Thenp 490 QD 2 ModelingApartmentDemand Theloweristherentalratep thelargeristhequantityofcloseapartmentsdemandedp QD Thequantitydemandedvs pricegraphisthemarketdemandcurveforcloseapartments MarketDemandCurveforApartments p QD ModelingApartmentSupply Supply Ittakestimetobuildmorecloseapartmentssointhisshort runthequantityavailableisfixed atsay100 MarketSupplyCurveforApartments p QS 100 CompetitiveMarketEquilibrium low rentalprice quantitydemandedofcloseapartmentsexceedsquantityavailable pricewillrise high rentalprice quantitydemandedlessthanquantityavailable pricewillfall CompetitiveMarketEquilibrium Quantitydemanded quantityavailable pricewillneitherrisenorfallsothemarketisatacompetitiveequilibrium CompetitiveMarketEquilibrium p QD QS 100 CompetitiveMarketEquilibrium p QD QS pe 100 CompetitiveMarketEquilibrium p QD QS pe 100 Peoplewillingtopaypeforcloseapartmentsgetcloseapartments CompetitiveMarketEquilibrium p QD QS pe 100 Peoplewillingtopaypeforcloseapartmentsgetcloseapartments Peoplenotwillingtopaypeforcloseapartmentsgetdistantapartments CompetitiveMarketEquilibrium Q Whorentsthecloseapartments A Thosemostwillingtopay Q Whorentsthedistantapartments A Thoseleastwillingtopay Sothecompetitivemarketallocationisby willingness to pay ComparativeStatics Whatisexogenousinthemodel priceofdistantapartmentsquantityofcloseapartmentsincomesofpotentialrenters Whathappensiftheseexogenousvariableschange ComparativeStatics Supposethepriceofdistantapartmentrises Demandforcloseapartmentsincreases rightwardshift causingahigherpriceforcloseapartments MarketEquilibrium p QD QS pe 100 MarketEquilibrium p QD QS pe 100 Higherdemand MarketEquilibrium p QD QS pe 100 Higherdemandcauseshighermarketprice samequantitytraded ComparativeStatics Supposethereweremorecloseapartments Supplyisgreater sothepriceforcloseapartmentsfalls MarketEquilibrium p QD QS pe 100 MarketEquilibrium p QD QS 100 Highersupply pe MarketEquilibrium p QD QS pe 100 Highersupplycausesalowermarketpriceandalargerquantitytraded ComparativeStatics Supposepotentialrenters incomesrise increasingtheirwillingness to payforcloseapartments Demandrises upwardshift causinghigherpriceforcloseapartments MarketEquilibrium p QD QS pe 100 MarketEquilibrium p QD QS pe 100 Higherincomescausehigherwillingness to pay MarketEquilibrium p QD QS pe 100 Higherincomescausehigherwillingness to pay highermarketprice andthesamequantitytraded TaxationPolicyAnalysis Localgovernmenttaxesapartmentowners Whathappenstopricequantityofcloseapartmentsrented Isanyofthetax passed torenters TaxationPolicyAnalysis Marketsupplyisunaffected Marketdemandisunaffected Sothecompetitivemarketequilibriumisunaffectedbythetax Priceandthequantityofcloseapartmentsrentedarenotchanged Landlordspayallofthetax ImperfectlyCompetitiveMarkets Amongstmanypossibilitiesare amonopolisticlandlordaperfectlydiscriminatorymonopolisticlandlordacompetitivemarketsubjecttorentcontrol AMonopolisticLandlord WhenthelandlordsetsarentalpricepherentsD p apartments Revenue pD p Revenueislowifp 0RevenueislowifpissohighthatD p 0 Anintermediatevalueforpmaximizesrevenue MonopolisticMarketEquilibrium p QD Lowprice Lowprice highquantitydemanded lowrevenue MonopolisticMarketEquilibrium p QD Highprice Highprice lowquantitydemanded lowrevenue MonopolisticMarketEquilibrium p QD Middleprice Middleprice mediumquantitydemanded largerrevenue MonopolisticMarketEquilibrium p QD QS Middleprice Middleprice mediumquantitydemanded largerrevenue Monopolistdoesnotrentallthecloseapartments 100 MonopolisticMarketEquilibrium p QD QS Middleprice Middleprice mediumquantitydemanded largerrevenue Monopolistdoesnotrentallthecloseapartments 100 Vacantcloseapartments PerfectlyDiscriminatoryMonopolisticLandlord Imaginethemonopolistkneweveryone swillingness to pay Charge 500tothemostwilling to pay charge 490tothe2ndmostwilling to pay etc DiscriminatoryMonopolisticMarketEquilibrium p QD QS 100 p1 500 1 DiscriminatoryMonopolisticMarketEquilibrium p QD QS 100 p1 500 p2 490 1 2 DiscriminatoryMonopolisticMarketEquilibrium p QD QS 100 p1 500 p2 490 1 2 p3 475 3 DiscriminatoryMonopolisticMarketEquilibrium p QD QS 100 p1 500 p2 490 1 2 p3 475 3 DiscriminatoryMonopolisticMarketEquilibrium p QD QS 100 p1 500 p2 490 1 2 p3 475 3 pe Discriminatorymonopolistchargesthecompetitivemarketpricetothelastrenter andrentsthecompetitivequantityofcloseapartments RentControl Localgovernmentimposesamaximumlegalprice pmax pe thecompetitiveprice MarketEquilibrium p QD QS pe 100 MarketEquilibrium p QD QS pe 100 pmax MarketEquilibrium p QD QS pe 100 pmax Excessdemand MarketEquilibrium p QD QS pe 100 pmax Excessdemand The100closeapartmentsarenolongerallocatedbywillingness to pay lottery lines largefamiliesfirst WhichMarketOutcomesAreDesirable Whichisbetter RentcontrolPerfectcompetitionMonopolyDiscriminatorymonopoly ParetoEfficiency VilfredoPareto 1848 1923 AParetooutcomeallowsno wastedwelfare i e theonlywayoneperson swelfarecanbeimprovedistoloweranotherperson swelfare ParetoEfficiency Jillhasanapartment Jackdoesnot Jillvaluestheapartmentat 200 Jackwouldpay 400forit JillcouldsublettheapartmenttoJackfor 300 Bothgain soitwasParetoinefficientforJilltohavetheapartment ParetoEfficiency AParetoinefficientoutcomemeansthereremainunrealizedmutualgains to trade Anymarketoutcomethatachievesallpossiblegains to trademustbeParetoefficient ParetoEfficiency Competitiveequilibrium allcloseapartmentrentersvaluethematthemarketpricepeormoreallothersvaluecloseapartmentsatlessthanpesonomutuallybeneficialtradesremainsotheoutcomeisParetoefficient ParetoEfficiency DiscriminatoryMonopoly assignmentofapartmentsisthesameaswiththeperfectlycompetitivemarketsothediscriminatorymonopolyoutcomeisalsoParetoefficient ParetoEfficiency Monopoly notallapartmentsareoccupiedsoadistantapartmentrentercouldbeassignedacloseapartmentandhavehigherwelfarewithoutloweringanybodyelse swelfare sothemonopolyoutcomeisParetoinefficient ParetoEfficiency RentControl somecloseapartmentsareassignedtorentersvaluingthematbelowthecompetitivepricepesomerentersvaluingacloseapartmentabovepedon tgetcloseapartmentsParetoinefficientoutcome HarderQuestions Overtime willthesupplyofcloseapartmentsincrease rentcontroldecreasethesupplyofapartments amonopolistsupplymoreapartmentsthanacompetitiverentalmarket ChapterTwo BudgetaryandOtherConstraintsonChoice ConsumptionChoiceSets Aconsumptionchoicesetisthecollectionofallconsumptionchoicesavailabletotheconsumer Whatconstrainsconsumptionchoice Budgetary timeandotherresourcelimitations BudgetConstraints Aconsumptionbundlecontainingx1unitsofcommodity1 x2unitsofcommodity2andsoonuptoxnunitsofcommoditynisdenotedbythevector x1 x2 xn Commoditypricesarep1 p2 pn BudgetConstraints Q Whenisaconsumptionbundle x1 xn affordableatgivenpricesp1 pn BudgetConstraints Q Whenisabundle x1 xn affordableatpricesp1 pn A Whenp1x1 pnxn mwheremistheconsumer s disposable income BudgetConstraints Thebundlesthatareonlyjustaffordableformtheconsumer sbudgetconstraint Thisistheset x1 xn x1 0 xn 0andp1x1 pnxn m BudgetConstraints Theconsumer sbudgetsetisthesetofallaffordablebundles B p1 pn m x1 xn x1 0 xn 0andp1x1 pnxn m Thebudgetconstraintistheupperboundaryofthebudgetset BudgetSetandConstraintforTwoCommodities x2 x1 Budgetconstraintisp1x1 p2x2 m m p1 m p2 BudgetSetandConstraintforTwoCommodities x2 x1 Budgetconstraintisp1x1 p2x2 m m p2 m p1 BudgetSetandConstraintforTwoCommodities x2 x1 Budgetconstraintisp1x1 p2x2 m m p1 Justaffordable m p2 BudgetSetandConstraintforTwoCommodities x2 x1 Budgetconstraintisp1x1 p2x2 m m p1 Justaffordable Notaffordable m p2 BudgetSetandConstraintforTwoCommodities x2 x1 Budgetconstraintisp1x1 p2x2 m m p1 Affordable Justaffordable Notaffordable m p2 BudgetSetandConstraintforTwoCommodities x2 x1 Budgetconstraintisp1x1 p2x2 m m p1 BudgetSet thecollectionofallaffordablebundles m p2 BudgetSetandConstraintforTwoCommodities x2 x1 p1x1 p2x2 misx2 p1 p2 x1 m p2soslopeis p1 p2 m p1 BudgetSet m p2 BudgetConstraints Ifn 3whatdothebudgetconstraintandthebudgetsetlooklike BudgetConstraintforThreeCommodities x2 x1 x3 m p2 m p1 m p3 p1x1 p2x2 p3x3 m BudgetSetforThreeCommodities x2 x1 x3 m p2 m p1 m p3 x1 x2 x3 x1 0 x2 0 x3 0andp1x1 p2x2 p3x3 m BudgetConstraints Forn 2andx1onthehorizontalaxis theconstraint sslopeis p1 p2 Whatdoesitmean BudgetConstraints Forn 2andx1onthehorizontalaxis theconstraint sslopeis p1 p2 Whatdoesitmean Increasingx1by1mustreducex2byp1 p2 BudgetConstraints x2 x1 Slopeis p1 p2 1 p1 p2 BudgetConstraints x2 x1 1 p1 p2 Opp costofanextraunitofcommodity1isp1 p2unitsforegoneofcommodity2 BudgetConstraints x2 x1 Opp costofanextraunitofcommodity1isp1 p2unitsforegoneofcommodity2 Andtheopp costofanextraunitofcommodity2isp2 p1unitsforegoneofcommodity1 p2 p1 1 BudgetSetsIncomeandPriceChanges Thebudgetconstraintandbudgetsetdependuponpricesandincome Whathappensaspricesorincomechange Howdothebudgetsetandbudgetconstraintchangeasincomemincreases Originalbudgetset x2 x1 Higherincomegivesmorechoice Originalbudgetset Newaffordableconsumptionchoices x2 x1 Originalandnewbudgetconstraintsareparallel sameslope Howdothebudgetsetandbudgetconstraintchangeasincomemdecreases Originalbudgetset x2 x1 Howdothebudgetsetandbudgetconstraintchangeasincomemdecreases x2 x1 New smallerbudgetset Consumptionbundlesthatarenolongeraffordable Oldandnewconstraintsareparallel BudgetConstraints IncomeChanges Increasesinincomemshifttheconstraintoutwardinaparallelmanner therebyenlargingthebudgetsetandimprovingchoice BudgetConstraints IncomeChanges Increasesinincomemshifttheconstraintoutwardinaparallelmanner therebyenlargingthebudgetsetandimprovingchoice Decreasesinincomemshifttheconstraintinwardinaparallelmanner therebyshrinkingthebudgetsetandreducingchoice BudgetConstraints IncomeChanges Nooriginalchoiceislostandnewchoicesareaddedwhenincomeincreases sohigherincomecannotmakeaconsumerworseoff Anincomedecreasemay typicallywill maketheconsumerworseoff BudgetConstraints PriceChanges Whathappensifjustonepricedecreases Supposep1decreases Howdothebudgetsetandbudgetconstraintchangeasp1decreasesfromp1 top1 Originalbudgetset x2 x1 m p2 m p1 m p1 p1 p2 Howdothebudgetsetandbudgetconstraintchangeasp1decreasesfromp1 top1 Originalbudgetset x2 x1 m p2 m p1 m p1 Newaffordablechoices p1 p2 Howdothebudgetsetandbudgetconstraintchangeasp1decreasesfromp1 top1 Originalbudgetset x2 x1 m p2 m p1 m p1 Newaffordablechoices Budgetconstraintpivots slopeflattensfrom p1 p2to p1 p2 p1 p2 p1 p2 BudgetConstraints PriceChanges Reducingthepriceofonecommoditypivotstheconstraintoutward Nooldchoiceislostandnewchoicesareadded soreducingonepricecannotmaketheconsumerworseoff BudgetConstraints PriceChanges Similarly increasingonepricepivotstheconstraintinwards reduceschoiceandmay typicallywill maketheconsumerworseoff UniformAdValoremSalesTaxes Anadvaloremsalestaxleviedatarateof5 increasesallpricesby5 frompto 1 0 05 p 1 05p Anadvaloremsalestaxleviedatarateoftincreasesallpricesbytpfrompto 1 t p Auniformsalestaxisapplieduniformlytoallcommodities UniformAdValoremSalesTaxes Auniformsalestaxleviedatratetchangestheconstraintfromp1x1 p2x2 mto 1 t p1x1 1 t p2x2 m UniformAdValoremSalesTaxes Auniformsalestaxleviedatratetchangestheconstraintfromp1x1 p2x2 mto 1 t p1x1 1 t p2x2 mi e p1x1 p2x2 m 1 t UniformAdValoremSalesTaxes x2 x1 p1x1 p2x2 m UniformAdValoremSalesTaxes x2 x1 p1x1 p2x2 m p1x1 p2x2 m 1 t UniformAdValoremSalesTaxes x2 x1 Equivalentincomelossis UniformAdValoremSalesTaxes x2 x1 Auniformadvaloremsalestaxleviedatratetisequivalenttoanincometaxleviedatrate TheFoodStampProgram Foodstampsarecouponsthatcanbelegallyexchangedonlyforfood Howdoesacommodity specificgiftsuchasafoodstampalterafamily sbudgetconstraint TheFoodStampProgram Supposem 100 pF 1andthepriceof othergoods ispG 1 ThebudgetconstraintisthenF G 100 TheFoodStampProgram G F 100 100 F G 100 beforestamps TheFoodStampProgram G F 100 100 F G 100 beforestamps TheFoodStampProgram G F 100 100 F G 100 beforestamps Budgetsetafter40foodstampsissued 140 40 TheFoodStampProgram G F 100 100 F G 100 beforestamps Budgetsetafter40foodstampsissued 140 Thefamily sbudgetsetisenlarged 40 TheFoodStampProgram Whatiffoodstampscanbetradedonablackmarketfor 0 50each TheFoodStampProgram G F 100 100 F G 100 beforestamps Budgetconstraintafter40foodstampsissued 140 120 Budgetconstraintwithblackmarkettrading 40 TheFoodStampProgram G F 100 100 F G 100 beforestamps Budgetconstraintafter40foodstampsissued 140 120 Blackmarkettradingmakesthebudgetsetlargeragain 40 BudgetConstraints RelativePrices Numeraire means unitofaccount Supposepricesandincomearemeasuredindollars Sayp1 2 p2 3 m 12 Thentheconstraintis2x1 3x2 12 BudgetConstraints RelativePrices Ifpricesandincomearemeasuredincents thenp1 200 p2 300 m 1200andtheconstraintis200 x1 300 x2 1200 thesameas2x1 3x2 12 Changingthenumerairechangesneitherthebudgetconstraintnorthebudgetset BudgetConstraints RelativePrices Theconstraintforp1 2 p2 3 m 122x1 3x2 12isalso1 x1 3 2 x2 6 theconstraintforp1 1 p2 3 2 m 6 Settingp1 1makescommodity1thenumeraireanddefinesallpricesrelativetop1 e g 3 2isthepriceofcommodity2relativetothepriceofcommodity1 BudgetConstraints RelativePrices Anycommoditycanbechosenasthenumerairewithoutchangingthebudgetsetorthebudgetconstraint BudgetConstraints RelativePrices p1 2 p2 3andp3 6 priceofcommodity2relativetocommodity1is3 2 priceofcommodity3relativetocommodity1is3 Relativepricesaretheratesofexchangeofcommodities2and3forunitsofcommodity1 ShapesofBudgetConstraints Q Whatmakesabudgetconstraintastraightline A Astraightlinehasaconstantslopeandtheconstraintisp1x1 pnxn msoifpricesareconstantsthenaconstraintisastraightline ShapesofBudgetConstraints Butwhatifpricesarenotconstants E g bulkbuyingdiscounts orpricepenaltiesforbuying toomuch Thenconstraintswillbecurved ShapesofBudgetConstraints QuantityDiscounts Supposep2isconstantat 1butthatp1 2for0 x1 20andp1 1forx1 20 ShapesofBudgetConstraints QuantityDiscounts Supposep2isconstantat 1butthatp1 2for0 x1 20andp1 1forx1 20 Thentheconstraint sslopeis 2 for0 x1 20 p1 p2 1 forx1 20andtheconstraintis ShapesofBudgetConstraintswithaQuantityDiscount m 100 50 100 20 Slope 2 1 2 p1 2 p2 1 Slope 1 1 1 p1 1 p2 1 80 x2 x1 ShapesofBudgetConstraintswithaQuantityDiscount m 100 50 100 20 Slope 2 1 2 p1 2 p2 1 Slope 1 1 1 p1 1 p2 1 80 x2 x1 ShapesofBudgetConstraintswithaQuantityDiscount m 100 50 100 20 80 x2 x1 BudgetSet BudgetConstraint ShapesofBudgetConstraintswithaQuantityPenalty x2 x1 BudgetSet BudgetConstraint ShapesofBudgetConstraints OnePriceNegative Commodity1isstinkygarbage Youarepaid 2perunittoacceptit i e p1 2 p2 1 Income otherthanfromacceptingcommodity1 ism 10 Thentheconstraintis 2x1 x2 10orx2 2x1 10 ShapesofBudgetConstraints OnePriceNegative 10 Budgetconstraint sslopeis p1 p2 2 1 2 x2 x1 x2 2x1 10 ShapesofBudgetConstraints OnePriceNegative 10 x2 x1 Budgetsetisallbundlesforwhichx1 0 x2 0andx2 2x1 10 MoreGeneralChoiceSets Choicesareusuallyconstrainedbymorethanabudget e g timeconstraintsandotherresourcesconstraints Abundleisavailableonlyifitmeetseveryconstraint MoreGeneralChoiceSets Food OtherStuff 10 Atleast10unitsoffoodmustbeeatentosurvive MoreGeneralChoiceSets Food OtherStuff 10 BudgetSet Choiceisalsobudgetconstrained MoreGeneralChoiceSets Food OtherStuff 10 Choiceisfurtherrestrictedbyatimeconstraint MoreGeneralChoiceSets Sowhatisthechoiceset MoreGeneralChoiceSets Food OtherStuff 10 MoreGeneralChoiceSets Food OtherStuff 10 MoreGeneralChoiceSets Food OtherStuff 10 Thechoicesetistheintersectionofalloftheconstraintsets ChapterThree Preferences RationalityinEconomics BehavioralPostulate Adecisionmakeralwayschoosesitsmostpreferredalternativefromitssetofavailablealternatives Sotomodelchoicewemustmodeldecisionmakers preferences PreferenceRelations Comparingtwodifferentconsumptionbundles xandy strictpreference xismorepreferredthanisy weakpreference xisasatleastaspreferredasisy indifference xisexactlyaspreferredasisy PreferenceRelations Strictpreference weakpreferenceandindifferenceareallpreferencerelations Particularly theyareordinalrelations i e theystateonlytheorderinwhichbundlesarepreferred PreferenceRelations denotesstrictpreference xymeansthatbundlexispreferredstrictlytobundley p p PreferenceRelations denotesstrictpreference xymeansbundlexispreferredstrictlytobundley denotesindifference x ymeansxandyareequallypreferred p p PreferenceRelations denotesstrictpreferencesoxymeansthatbundlexispreferredstrictlytobundley denotesindifference x ymeansxandyareequallypreferred denotesweakpreference xymeansxispreferredatleastasmuchasisy p p PreferenceRelations xyandyximplyx y PreferenceRelations xyandyximplyx y xyand notyx implyxy p AssumptionsaboutPreferenceRelations Completeness Foranytwobundlesxandyitisalwayspossibletomakethestatementthateitherxyoryx AssumptionsaboutPreferenceRelations Reflexivity Anybundlexisalwaysatleastaspreferredasitself i e xx AssumptionsaboutPreferenceRelations Transitivity Ifxisatleastasprefer