经济学原理 曼昆第七版第四讲讲义：Supply and Demand

Chapter4SupplyandDemandFall20171Questions•Ifyouaremakingrealestateinvestmentdecisions,howwouldyoupredicttheeffectofthepolicychanges?•WhataretherealfactordrivingtheresidentialhousingpriceinChina?•Whatarethelong-runperspectivesofChineserealestatemarkets?2TheMarketMechanism•AMarketisamechanismthroughwhichbuyersandsellersinteracttodeterminepricesandexchangegoods,services,andassets–Geographicalarea;–Timeperiod;–Good/servicebeingtraded•The“indivisiblehand”–Nosingleindividualororganizationorgovernmentisresponsibleforsolvingtheeconomicproblemsinamarketeconomy–Oursociety,despiteofitsfragility(surprise!),functionswellformostofthetimeinaspontaneousmanner•Toknowhowmarkethelptosolvetheimportantquestionsandtobefamiliarwiththefollowingeconomicconcepts,weneedtostudythedemandandsupplymodel(D-Smodel)–Price;marketequilibrium;efficiency3MarketsandCompetition•Supplyanddemand–Wordseconomistsusemostoften–Theforcesthatmakemarketeconomieswork–Refertothebehaviorofpeopleastheyinteractwithoneanotherincompetitivemarkets4MarketsandCompetition•Market–Agroupofbuyersandsellersofaparticulargoodorservice–Buyersasagroup•Determinethedemandfortheproduct–Sellersasagroup•Determinethesupplyoftheproduct5MarketsandCompetition•Marketstakemanyforms–Highlyorganized•Marketsformanyagriculturalcommodities–Lessorganized•Marketforicecreaminaparticulartown6MarketsandCompetition•Competitivemarket–Marketinwhichtherearemanybuyersandmanysellers–Eachhasanegligibleimpactonmarketprice–Priceandquantityaredeterminedbyallbuyersandsellers•Astheyinteractinthemarketplace7MarketsandCompetition•Perfectlycompetitivemarket–Goodsofferedforsaleareallexactlythesame–Buyersandsellersaresonumerous•Nosinglebuyerorsellerhasanyinfluenceoverthemarketprice•Pricetakers–Atthemarketprice•Buyerscanbuyalltheywant•Sellerscansellalltheywant8MarketsandCompetition•Monopoly–Theonlysellerinthemarket–Setstheprice•Othermarkets–Betweenperfectcompetitionandmonopoly9Demand•Quantitydemanded–Amountofagoodthatbuyersarewillingandabletopurchase•Lawofdemand–Otherthingsequal–Whenthepriceofagoodrises,thequantitydemandedofthegoodfalls–Whenthepricefalls,thequantitydemandedrises10Demand•Demand–Relationshipbetweenthepriceofagoodandquantitydemanded–Demandschedule:atable–Demandcurve:agraph•Priceontheverticalaxis•Quantityonthehorizontalaxis•Individualdemand–Anindividual’sdemandforaproduct11Figure1Catherine’sDemandScheduleandDemandCurveDemandcurveThedemandscheduleisatablethatshowsthequantitydemandedateachprice.Thedemandcurve,whichgraphsthedemandschedule,illustrateshowthequantitydemandedofthegoodchangesasitspricevaries.Becausealowerpriceincreasesthequantitydemanded,thedemandcurveslopesdownward.PriceofIce-CreamConeQuantityofConesDemanded$0.000.501.001.502.002.503.0012cones10864200121011912345678QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamCones1.Adecreaseinprice...2....increasesquantityofconesdemanded.12Demand•Marketdemand–Sumofallindividualdemandsforagoodorservice•Marketdemandcurve–Sumtheindividualdemandcurveshorizontally–Totalquantitydemandedofagoodvaries•Asthepriceofthegoodvaries•Otherthingsconstant13Figure2MarketDemandastheSumofIndividualDemandsThequantitydemandedinamarketisthesumofthequantitiesdemandedbyallthebuyersateachprice.Thus,themarketdemandcurveisfoundbyaddinghorizontallytheindividualdemandcurves.Atapriceof$2.00,Catherinedemands4ice-creamcones,andNicholasdemands3ice-creamcones.Thequantitydemandedinthemarketatthispriceis7cones.14Figure2MarketDemandastheSumofIndividualDemandsDCatherine0121011912345678QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamConesCatherine’sdemandDNicholas01234567QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamConesNicholas’sdemand+=DMarket018246810121416QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamConesMarketdemand15Demand•Shiftsinthedemandcurve–Increaseindemand•Anychangethatincreasesthequantitydemandedateveryprice•Demandcurveshiftsright–Decreaseindemand•Anychangethatdecreasesthequantitydemandedateveryprice•Demandcurveshiftsleft16Figure3ShiftsintheDemandCurvePriceofIce-CreamConesQuantityofIce-CreamCones0Demandcurve,D1Demandcurve,D3Demandcurve,D2IncreaseinDemandDecreaseinDemandAnychangethatraisesthequantitythatbuyerswishtopurchaseatanygivenpriceshiftsthedemandcurvetotheright.Anychangethatlowersthequantitythatbuyerswishtopurchaseatanygivenpriceshiftsthedemandcurvetotheleft.17Demand•Variablesthatcanshiftthedemandcurve–Income–Pricesofrelatedgoods–Tastes–Expectations–Numberofbuyers18Demand•Income–Normalgood•Otherthingsconstant•Anincreaseinincomeleadstoanincreaseindemand–Inferiorgood•Otherthingsconstant•Anincreaseinincomeleadstoadecreaseindemand19Demand•Pricesofrelatedgoods–Substitutes,twogoods•Anincreaseinthepriceofone•Leadstoanincreaseinthedemandfortheother–Complements,twogoods•Anincreaseinthepriceofone•Leadstoadecreaseinthedemandfortheother20Demand•Tastes–Changeintastes:changesthedemand•Expectationsaboutthefuture–Expectanincreaseinincome•Increaseincurrentdemand–Expecthigherprices•Increaseincurrentdemand•Numberofbuye