讲义 均衡PPT课件

1、Market Equilibrium A market is in equilibrium when total quantity demanded by buyers equals total quantity supplied by sellers.第1页/共85页Market EquilibriumpD(p), S(p)q=D(p)MarketdemandMarketsupplyq=S(p)第2页/共85页Market EquilibriumpD(p), S(p)q=D(p)MarketdemandMarketsupplyq=S(p)p*q*D(p*) = S(p*); the mark

2、etis in equilibrium.第3页/共85页Market EquilibriumpD(p), S(p)q=D(p)MarketdemandMarketsupplyq=S(p)p*S(p)D(p) S(p); an excessof quantity supplied overquantity demanded.pD(p)第4页/共85页Market EquilibriumpD(p), S(p)q=D(p)MarketdemandMarketsupplyq=S(p)p*S(p)D(p) S(p”); an excessof quantity demandedover quantity

3、 supplied.p”S(p”)第6页/共85页Market EquilibriumpD(p), S(p)q=D(p)MarketdemandMarketsupplyq=S(p)p*D(p”)D(p”) S(p”); an excessof quantity demandedover quantity supplied.p”S(p”)Market price must rise towards p*.第7页/共85页Market Equilibrium Linear D & SD pabp( ) S pcdp( ) At the equilibrium price p*, D(p*)

4、 = S(p*).That is,abpcdp *which givespacbd* andqD pS padbcbd*()(). 第8页/共85页Market EquilibriumpD(p), S(p)D(p) = a-bpMarketdemandMarketsupplyS(p) = c+dppacbd* dbbcadq* 第9页/共85页Market Equilibrium Can we calculate the market equilibrium using the inverse market demand and supply curves? Yes, it is the sa

5、me calculation.第10页/共85页Market EquilibriumqD pabppaqbDq ( )( ),1qS pcdppcqdSq ( )( ),1the equation of the inverse marketdemand curve. Andthe equation of the inverse marketsupply curve.第11页/共85页Market EquilibriumqD-1(q),S-1(q)D-1(q) = (a-q)/bMarket inversedemandS-1(q) = (-c+q)/dp*q*At equilibrium,D-1

6、(q*) = S-1(q*).Market inverse supply第12页/共85页Market EquilibriumpDqaqb 1( )pSqcqd 1( ).andAt the equilibrium quantity q*, D-1(p*) = S-1(p*).That is,aqbcqd *which givesqadbcbd* andpDqSqacbd*()(). 11第13页/共85页Market EquilibriumqD-1(q),S-1(q)D-1(q) = (a-q)/bMarketdemandMarketsupplyS-1(q) = (-c+q)/dpacbd*

7、 dbbcadq* 第14页/共85页Market Equilibrium Two special cases: quantity supplied is fixed, independent of the market price, and quantity supplied is extremely sensitive to the market price.第15页/共85页Market EquilibriumS(p) = c+dp, so d=0and S(p) c.pqq* = cMarket quantity supplied isfixed, independent of pri

8、ce.第16页/共85页Market EquilibriumS(p) = c+dp, so d=0and S(p) c.pqp*D-1(q) = (a-q)/bMarketdemandq* = cMarket quantity supplied isfixed, independent of price.第17页/共85页Market EquilibriumS(p) = c+dp, so d=0and S(p) c.pq p* =(a-c)/bD-1(q) = (a-q)/bMarketdemandq* = cp* = D-1(q*); that is,p* = (a-c)/b.Market

9、quantity supplied isfixed, independent of price.第18页/共85页Market EquilibriumS(p) = c+dp, so d=0and S(p) c.pqD-1(q) = (a-q)/bMarketdemandq* = cp* = D-1(q*); that is,p* = (a-c)/b.pacbd* qadbcbd* with d = 0 givepacb* qc*. p* =(a-c)/bMarket quantity supplied isfixed, independent of price.第19页/共85页Market

10、EquilibriumMarket quantity supplied isextremely sensitive to price.S-1(q) = p*.pqp*第20页/共85页Market EquilibriumMarket quantity supplied isextremely sensitive to price.S-1(q) = p*.pqp*D-1(q) = (a-q)/bMarketdemandq*第21页/共85页Market EquilibriumMarket quantity supplied isextremely sensitive to price.S-1(q

11、) = p*.pqp*D-1(q) = (a-q)/bMarketdemandq* =a-bp*p* = D-1(q*) = (a-q*)/b soq* = a-bp*第22页/共85页Quantity Taxes A quantity tax levied at a rate of $t is a tax of $t paid on each unit traded. If the tax is levied on sellers then it is an excise tax. If the tax is levied on buyers then it is a sales tax.第

12、23页/共85页Quantity Taxes What is the effect of a quantity tax on a markets equilibrium? How are prices affected? How is the quantity traded affected? Who pays the tax? How are gains-to-trade altered?第24页/共85页Quantity Taxes A tax rate t makes the price paid by buyers, pb, higher by t from the price rec

13、eived by sellers, ps.pptbs 第25页/共85页Quantity Taxes Even with a tax the market must clear. I.e. quantity demanded by buyers at price pb must equal quantity supplied by sellers at price ps.D pS pbs()() 第26页/共85页Quantity Taxespptbs D pS pbs()() anddescribe the markets equilibrium.Notice that these two

14、conditions apply nomatter if the tax is levied on sellers or onbuyers.Hence, a sales tax rate $t has thesame effect as an excise tax rate $t.第27页/共85页Quantity Taxes & Market EquilibriumpD(p), S(p)MarketdemandMarketsupplyp*q*No tax第28页/共85页Quantity Taxes & Market EquilibriumpD(p), S(p)Marketd

15、emandMarketsupplyp*q*$tAn excise taxraises the marketsupply curve by $t第29页/共85页Quantity Taxes & Market EquilibriumpD(p), S(p)MarketdemandMarketsupplyp*q*An excise taxraises the marketsupply curve by $t,raises the buyersprice and lowers thequantity traded.$tpbqt第30页/共85页Quantity Taxes & Mark

16、et EquilibriumpD(p), S(p)MarketdemandMarketsupplyp*q*An excise taxraises the marketsupply curve by $t,raises the buyersprice and lowers thequantity traded.$tpbqtAnd sellers receive only ps = pb - t.ps第31页/共85页Quantity Taxes & Market EquilibriumpD(p), S(p)MarketdemandMarketsupplyp*q*No tax第32页/共8

17、5页Quantity Taxes & Market EquilibriumpD(p), S(p)MarketdemandMarketsupplyp*q*An sales tax lowersthe market demandcurve by $t$t第33页/共85页Quantity Taxes & Market EquilibriumpD(p), S(p)MarketdemandMarketsupplyp*q*An sales tax lowersthe market demandcurve by $t, lowersthe sellers price andreduces

18、the quantitytraded.$tqtps第34页/共85页Quantity Taxes & Market EquilibriumpD(p), S(p)MarketdemandMarketsupplyp*q*An sales tax lowersthe market demandcurve by $t, lowersthe sellers price andreduces the quantitytraded.$tpbpbqtpbAnd buyers pay pb = ps + t.ps第35页/共85页Quantity Taxes & Market Equilibri

19、umpD(p), S(p)MarketdemandMarketsupplyp*q*A sales tax levied atrate $t has the sameeffects on themarkets equilibriumas does an excise taxlevied at rate $t.$tpbpbqtpbps$t第36页/共85页Quantity Taxes & Market Equilibrium Who pays the tax of $t per unit traded? The division of the $t between buyers and s

20、ellers is the incidence of the tax (税收分担).第37页/共85页Quantity Taxes & Market EquilibriumpD(p), S(p)MarketdemandMarketsupplyp*q*pbpbqtpbps第38页/共85页Quantity Taxes & Market EquilibriumpD(p), S(p)MarketdemandMarketsupplyp*q*pbpbqtpbpsTax paid by buyers第39页/共85页Quantity Taxes & Market Equilibri

21、umpD(p), S(p)MarketdemandMarketsupplyp*q*pbpbqtpbpsTax paid by sellers第40页/共85页Quantity Taxes & Market EquilibriumpD(p), S(p)MarketdemandMarketsupplyp*q*pbpbqtpbpsTax paid by buyersTax paid by sellers第41页/共85页Quantity Taxes & Market Equilibrium E.g. suppose the market demand and supply curve

22、s are linear.D pabpbb() S pcdpss() 第42页/共85页Quantity Taxes & Market EquilibriumandD pabpbb() S pcdpss(). 第43页/共85页Quantity Taxes & Market EquilibriumandWith the tax, the market equilibrium satisfiesandsoandD pabpbb() S pcdpss(). pptbs D pS pbs()() pptbs abpcdpbs .第44页/共85页Quantity Taxes &

23、; Market EquilibriumD pabpbb() S pcdpss(). andWith the tax, the market equilibrium satisfiespptbs D pS pbs()() andsopptbs abpcdpbs .andSubstituting for pb givesab ptcdppacbtbdsss ().第45页/共85页Quantity Taxes & Market Equilibriumpacbtbds andpptbs giveThe quantity traded at equilibrium isqD pS pabpa

24、dbcbdtbdtbsb ()().pacdtbdb 第46页/共85页Quantity Taxes & Market Equilibriumpacbtbds pacdtbdb qadbcbdtbdt As t 0, ps and pb theequilibrium price ifthere is no tax (t = 0) and qt the quantity traded at equilibriumwhen there is no tax.adbcbd ,*,pdbca 第47页/共85页Quantity Taxes & Market Equilibriumpacb

25、tbds pacdtbdb qadbcbdtbdt As t increases, ps falls,pb rises, andqt falls.第48页/共85页Quantity Taxes & Market Equilibriumpacbtbds pacdtbdb qadbcbdtbdt The tax paid per unit by the buyer isppacdtbdacbddtbdb *.第49页/共85页Quantity Taxes & Market Equilibriumpacbtbds pacdtbdb qadbcbdtbdt The tax paid p

26、er unit by the buyer isppacdtbdacbddtbdb *.The tax paid per unit by the seller isppacbdacbtbdbtbds*. 第50页/共85页Quantity Taxes & Market Equilibriumpacbtbds pacdtbdb qadbcbdtbdt The total tax paid (by buyers and sellerscombined) isTtqtadbcbdtbdt .第51页/共85页Tax Incidence and Own-Price Elasticities Th

27、e incidence of a quantity tax depends upon the own-price elasticities of demand and supply.第52页/共85页Tax Incidence and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*$tpbqtps第53页/共85页Tax Incidence and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*$tpbqtpsChange to buyersp

28、rice is pb - p*.Change to quantitydemanded is Dq.Dq第54页/共85页Tax Incidence and Own-Price ElasticitiesAround p = p* the own-price elasticityof demand is approximately Dbqqppp D D*第55页/共85页Tax Incidence and Own-Price ElasticitiesAround p = p* the own-price elasticityof demand is approximately DbbDqqppp

29、ppqpq D DD D*.第56页/共85页Tax Incidence and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*$tpbqtps第57页/共85页Tax Incidence and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*$tpbqtpsChange to sellersprice is ps - p*.Change to quantitydemanded is Dq.Dq第58页/共85页Tax Incidence an

30、d Own-Price ElasticitiesAround p = p* the own-price elasticityof supply is approximately Ssqqppp D D*第59页/共85页Tax Incidence and Own-Price ElasticitiesAround p = p* the own-price elasticityof supply is approximately SssSqqpppppqpq D DD D*.第60页/共85页Tax Incidence and Own-Price ElasticitiespD(p), S(p)Ma

31、rketdemandMarketsupplyp*q*pbpbqtpbpsTax paid by buyersTax paid by sellers第61页/共85页Tax Incidence and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*pbpbqtpbpsTax paid by buyersTax paid by sellersTax incidence = ppppbs *.第62页/共85页Tax Incidence and Own-Price ElasticitiesTax incidence = pp

32、ppbs *.ppqpqbD *.D D ppqpqsS *.D D 第63页/共85页Tax Incidence and Own-Price ElasticitiesTax incidence = ppppbs *.ppqpqbD *.D D ppqpqsS *.D D SoppppbsSD *. 第64页/共85页Tax Incidence and Own-Price ElasticitiesppppbsSD *. Tax incidence isThe fraction of a $t quantity tax paidby buyers rises as supply becomes

33、moreown-price elastic or as demand becomesless own-price elastic.第65页/共85页Tax Incidence and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*$tpbqtpsAs market demandbecomes less own-price elastic, taxincidence shifts moreto the buyers. 第66页/共85页Tax Incidence and Own-Price ElasticitiespD(

34、p), S(p)MarketdemandMarketsupplyp*q*$tpbqtpsAs market demandbecomes less own-price elastic, taxincidence shifts moreto the buyers. 第67页/共85页Tax Incidence and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyps= p*$tpbqt = q*As market demandbecomes less own-price elastic, taxincidence shifts

35、moreto the buyers. 第68页/共85页Tax Incidence and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyps= p*$tpbqt = q*As market demandbecomes less own-price elastic, taxincidence shifts moreto the buyers. When D = 0, buyers pay the entire tax, even though it is levied on the sellers.第69页/共85页Tax I

36、ncidence and Own-Price ElasticitiesppppbsSD *. Tax incidence isSimilarly, the fraction of a $t quantitytax paid by sellers rises as supplybecomes less own-price elastic or asdemand becomes more own-price elastic.第70页/共85页Deadweight Loss and Own-Price Elasticities A quantity tax imposed on a competit

37、ive market reduces the quantity traded and so reduces gains-to-trade (i.e. the sum of Consumers and Producers Surpluses). The lost total surplus is the taxs deadweight loss（额外净损失）, or excess burden.第71页/共85页Deadweight Loss and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*No tax第72页/共

38、85页Deadweight Loss and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*No taxCS第73页/共85页Deadweight Loss and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*No taxPS第74页/共85页Deadweight Loss and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*No taxCSPS第75页/共85页Deadweight Loss and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*$tpbqtpsCSPSThe tax reducesboth CS and PS第76页/共85页Deadweight Loss and Own-Price ElasticitiespD(p), S(p)MarketdemandMarketsupplyp*q*$tpbqtpsCSPSThe tax reducesboth CS and PS,transfe