弹性及其应用

1、5P R I N C I P L E S O FF O U R T H E D I T I O NElasticity and its Application共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONIn this chapter, look for the answers to these questions:What is elasticity? What kinds of issues can elasticity help us understand?What is the price elasticity of demand? How

2、is it related to the demand curve? How is it related to revenue & expenditure?What is the price elasticity of supply? How is it related to the supply curve? What are the income and cross-price elasticities of demand? 共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATION你设计网站给当地的贸易公司，每份网站的售价是$200 ，你每个月能卖掉12份

3、。现在你的成本上升了（包括时间的机会成本），所以你决定把网站售价提高到$250 。需求规律说明你的价格如果提高，销售量就一定减少。那么网站的销售量减少了多少(dusho)？你的总收益是下降了还是上升了？情景(qngjng)设计.0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONElasticityBasic idea: Elasticity measures how much one variable responds to changes in another variable. One type of elasticity measures how

4、 much demand for your websites will fall if you raise your price. Definition: Elasticity is a numerical measure of the responsiveness of Qd or Qs to one of its determinants. 0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONPrice Elasticity of DemandPrice elasticity of demand measures how much Qd respon

5、ds to a change in P.Price elasticity of demand=Percentage change in QdPercentage change in PLoosely speaking, it measures the price-sensitivity of buyers demand. 0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONPrice Elasticity of Demand0PQDQ2P2P1Q1P rises by 10%Q falls by 15%15%10%= 1.5Price elasticit

6、y of demand=Percentage change in QdPercentage change in PPrice elasticity of demand equals Example:共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONPrice Elasticity of Demand沿着需求曲线， P和Q 呈反方向移动，需求价格弹性是负数。我们遵循一般做法，去掉负号(f ho)，把所有价格弹性表示为正数。0PQDQ2P2P1Q1Price elasticity of demand=Percentage change in QdPercen

7、tage change in P共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONCalculating Percentage Changes0PQD$2508B$20012ADemand for your websitesStandard method of computing the percentage (%) change:end value start valuestart valuex 100%Going from A to B, the % change in P equals($250$200)/$200 = 25%共七十八页CHAPTE

8、R 5 ELASTICITY AND ITS APPLICATIONCalculating Percentage Changes0PQD$2508B$20012ADemand for your websitesProblem: The standard method gives different answers depending on where you start. From A to B, P rises 25%, Q falls 33%,elasticity = 33/25 = 1.33From B to A, P falls 20%, Q rises 50%, elasticity

9、 = 50/20 = 2.50 共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONCalculating Percentage Changes所以(suy)，我们用中点法代替： 0最后水平 原先水平中点值x 100%中点法式用变动量除以原先水平与最后水平的中点值（或平均值）来计算变动百分比。 无论变动的方向(fngxing)如何，中点法给出的答案都是相同的。共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONCalculating Percentage ChangesUsing the midpoint method

10、, the % change in P equals0$250 $200$225x 100%= 22.2%The % change in Q equals12 810 x 100%= 40.0%The price elasticity of demand equals40/22.2 = 1.8共七十八页A C T I V E L E A R N I N G 1: 弹性(tnxng)的计算用下列(xili)信息计算饭店的需求价格弹性:if P = $70, Qd = 5000if P = $90, Qd = 300012共七十八页A C T I V E L E A R N I N G 1: An

11、swers用中点法计算(j sun)：% change in Qd(5000 3000)/4000 = 50% change in P($90 $70)/$80 = 25%The price elasticity of demand equals1350%25%= 2.0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATION需求价格(jig)弹性的决定因素为了学习价格弹性的决定因素，我们将下列的物品(wpn)进行比较：在每个例子中：假设两种物品价格都上升20%. 需求量下降的多的物品的需求价格弹性最大。这是一种什么样的物品？为什么？决定需求价格弹性大小的因素

12、是什么？0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONEXAMPLE 1:爆米花 vs. 防晒霜 两种物品(wpn)的价格都上升20%。哪种物品Qd下降的多？为什么？爆米花有大量的近似替代品 所以价格上升时，买者很容易转向。 防晒霜没有近似替代品，所以如果价格上升，消费者不可能离开很多。 Lesson: 有相近替代品的物品的需求往往较富有弹性。Price elasticity is higher when close substitutes are available. 0共七十八页CHAPTER 5 ELASTICITY AND ITS APPL

13、ICATIONEXAMPLE 2:牛仔裤 vs. 衣服(y fu)两种物品的价格都上升20%，哪种物品的需求量下降(xijing)多？为是么？牛仔裤是一个较狭义的的范畴，有许多替代品。 衣服是一个广泛的范畴，几乎找不到衣服的替代品。 Lesson: 范围小的市场的需求弹性往往大于范围大的市场的需求弹性。Price elasticity is higher for narrowly defined goods than broadly defined ones. 0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONEXAMPLE 3:胰岛素 vs. 加勒比

14、海(ji l b hi)旅游两种物品价格都上升20%。哪种物品的Qd 需求量下降的多？为什么？对于千百万患者来说，看病是必须的，即使价格上升也几乎不会减少需求。 对于奢侈品来说，如果价格上升，许多(xdu)人就会忘记它。 Lesson: 奢侈品的价格弹性大于必需品。Price elasticity is higher for luxuries than for necessities. 0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONEXAMPLE 4:短期内的汽油(qyu)供给 vs. 长期汽油供给如果汽油(qyu)的价格上升20%，需求量的下降短

15、期大还是长期打？为什么？短期内很少有人会离开。 长期内，人们可以购买小型汽车，或办理到里工作地点近的地方。 Lesson: 物品的需求弹性长期比短期的需求价格弹性大。Price elasticity is higher in the long run than the short run. 0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATION价格弹性的决定因素(yn s)：小结 需求价格弹性(tnxng)取决于：近似替代品的可获得性；必需品与奢侈品；物品的市场定义范围宽还是窄；时间框架：长期比短期具有更高的价格弹性。 0共七十八页CHAPTER 5 EL

16、ASTICITY AND ITS APPLICATIONThe Variety of Demand CurvesThe price elasticity of demand is closely related to the slope of the demand curve. Rule of thumb: The flatter the curve, the bigger the elasticity. The steeper the curve, the smaller the elasticity. Five different classifications of D curves.0

17、共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONQ1P1D“Perfectly inelastic demand” (one extreme case)PQP2P falls by 10%Q changes by 0%00%10%= 0Price elasticity of demand=% change in Q% change in P=Consumers price sensitivity:D curve:Elasticity:vertical00共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIOND“Ine

18、lastic demand”PQQ1P1Q2P2Q rises less than 10%0 10%10% 1Price elasticity of demand=% change in Q% change in P=P falls by 10%Consumers price sensitivity:D curve:Elasticity:relatively steeprelatively low 10%10% 1Price elasticity of demand=% change in Q% change in P=P falls by 10%Consumers price sensiti

19、vity:D curve:Elasticity:relatively flatrelatively high 1共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIOND“Perfectly elastic demand” (the other extreme)PQP1Q1P changes by 0%Q changes by any %0any %0%= infinityQ2P2 =Consumers price sensitivity:D curve:Elasticity:infinityhorizontalextremePrice elasticity

20、of demand=% change in Q% change in P=共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONElasticity of a Linear Demand Curve0The slope of a linear demand curve is constant, but its elasticity is not. PQ$302010$00204060200%40%= 5.0E =67%67%= 1.0E =40%200%= 0.2E =共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATION

21、总收益与需求价格(jig)弹性继续我们的情景，如果你把网站的售价from $200 to $250，你的总收益是上升还是下降？Revenue = P x Q 价格上升对于总收益来说具有两种影响;提高价格意味着提高了每单位的销售收益； 但是由于需求定理(dngl)的存在，需求量降低了。这两种影响哪个更大一些？取决于需求价格弹性。 0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONPrice Elasticity and Total Revenue如果需求是富有弹性(tnxng)的，即需求价格弹性(tnxng) 1 % change in Q % chan

22、ge in P由于需求量变化导致的总收益的下降比由于价格上升导致的总收益的上升大一些，所以总收益下降。 Revenue = P x Q Price elasticity of demand=Percentage change in QPercentage change in P0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONPrice Elasticity and Total RevenueElastic demand(elasticity = 1.8)PQD$20012If P = $200, Q = 12 and revenue = $2400.

23、 当D富有弹性时，价格(jig)上升导致总收益下降。 0$2508If P = $250, Q = 8 and revenue = $2000.由于需求量的减少(jinsho)导致的总收益的减少(jinsho)由于价格上升导致的总收益的增加共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONPrice Elasticity and Total Revenue如果需求是缺乏弹性(tnxng)的，即需求价格弹性(tnxng)1， % change in Q % change in P如果Q 下降导致的总收益减少的量小于价格上升导致的总收益增加的量，则总收益上升

24、。 在我们的案例中，当价格上升到$250，假设需求量只减少到10，而不是8。 Revenue = P x Q Price elasticity of demand=Percentage change in QPercentage change in P0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONPrice Elasticity and Total RevenueNow, demand is inelastic: elasticity = 0.82PQD$20012If P = $200, Q = 12 and revenue = $2400. $

25、25010If P = $250, Q = 10 and revenue = $2500.当D时缺乏弹性时，价格上升将导致总收益(shuy)增加。 0lost revenue due to lower Qincreased revenue due to higher P共七十八页A C T I V E L E A R N I N G 2: 弹性(tnxng)和与出额或总收益胰岛素的药品价格(jig)上升10%，对胰岛素的总支出是上升了还是下降了？旅游奢侈品的价格下降20%，对旅游奢侈品的总收益是上升还是下降了？32共七十八页A C T I V E L E A R N I N G 2: Answ

26、ers33A.胰岛素的药品(yopn)价格上升10%，对胰岛素的总支出是上升了还是下降了？消费总额 = P x Q 由于需求是缺乏弹性的， Q 的减少小于10%，所以，总的支出额上升。共七十八页A C T I V E L E A R N I N G 2: Answers34B.旅游奢侈品的价格下降20%，对旅游奢侈品的总收益是上升还是下降了？Revenue = P x Q价格下降导致总收益减少(jinsho)，但是需求量增加导致总收益增加，哪个影响更大一些？由于富有弹性， Q 的增加大于20%，所以，总收益增加。共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICA

27、TION禁毒增加(zngji)还是减少了与毒品相关的犯罪非法毒品的使用会导致犯罪，经常使用毒品的人会对其行为失去控制力，从而导致犯罪。我们设计两种政策来减少非法毒品的使用，并分析其对于毒品相关犯罪的影响。为了简单(jindn)起见，我们假设与毒品相关的犯罪量等于毒品的总支出额。非法毒品的需求是缺乏弹性的，因此，禁毒会增加与毒品相关的犯罪。 0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIOND1政策(zhngc) 1: 禁毒0Price of DrugsQuantity of DrugsS1S2P1Q1P2Q2禁毒减少(jinsho)了毒品的供给.由于毒

28、品的需求是缺乏弹性的，价格上升的幅度要大于需求量减少到幅度。结论：毒品支出的货币总量增加了，并且增加了与毒品相关的犯罪。现在的毒品相关的犯罪原来的毒品相关的犯罪共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATION政策(zhngc) 2: 禁毒教育0Price of DrugsQuantity of DrugsD1SP1Q1D2P2Q2毒品(dpn)教育减少了毒品(dpn)的需求.P and Q fall. 结论：毒品的货币总支出减少了，并减少了与毒品相关的犯罪。 原来的毒品相关的犯罪现在的毒品相关的犯罪共七十八页CHAPTER 5 ELASTICITY A

29、ND ITS APPLICATIONPrice Elasticity of SupplyPrice elasticity of supply measures how much Qs responds to a change in P.Price elasticity of supply=Percentage change in QsPercentage change in PLoosely speaking, it measures the price-sensitivity of sellers supply. Again, use the midpoint method to compu

30、te the percentage changes. 0共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONQ2Price Elasticity of SupplyPrice elasticity of supply equals 0PQSP2Q1P1P rises by 8%Q rises by 16%16%8%= 2.0Price elasticity of supply=Percentage change in QsPercentage change in PExample:共七十八页CHAPTER 5 ELASTICITY AND ITS APPL

31、ICATIONThe Variety of Supply CurvesThe slope of the supply curve is closely related to price elasticity of supply. Rule of thumb: The flatter the curve, the bigger the elasticity. The steeper the curve, the smaller the elasticity.Five different classifications.0共七十八页CHAPTER 5 ELASTICITY AND ITS APPL

32、ICATIONS“Perfectly inelastic” (one extreme)PQQ1P1P2Q changes by 0%00%10%= 0Price elasticity of supply=% change in Q% change in P=P rises by 10%Sellers price sensitivity:S curve:Elasticity:vertical00共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONS“Inelastic”PQQ1P1Q2P2Q rises less than 10%0 10%10% 1Pric

33、e elasticity of supply=% change in Q% change in P=P rises by 10%Sellers price sensitivity:S curve:Elasticity:relatively steeprelatively low 10%10% 1Price elasticity of supply=% change in Q% change in P=P rises by 10%Sellers price sensitivity:S curve:Elasticity:relatively flatrelatively high 1共七十八页CH

34、APTER 5 ELASTICITY AND ITS APPLICATIONS“Perfectly elastic” (the other extreme)PQP1Q1P changes by 0%Q changes by any %0any %0%= infinityPrice elasticity of supply=% change in Q% change in P=Q2P2 =Sellers price sensitivity:S curve:Elasticity:horizontalextremeinfinity共七十八页CHAPTER 5 ELASTICITY AND ITS A

35、PPLICATION供给价格(jig)弹性及其决定因素如果卖者很容易改变他们所生产的物品(wpn)，供给的价格弹性就大。 例如： 海滩土地的供给的改变几乎是不可能的，所以，他的供给价格弹性小于汽车。 对于大多数物品来说，长期中的供给价格弹性要大于短期，因为长期中，企业可以开设新的工厂，原来的工厂可以进入新的市场。共七十八页A C T I V E L E A R N I N G 3: 弹性(tnxng)与均衡点的变化海滩土地的供给是缺乏弹性的，新汽车的供给是富有弹性的。 假设由于人口增加(zngji)导致两种物品的需求都增加(zngji)。 (在每一种价格下，需求量都增加). 哪种物品价格变化最

36、多？哪种物品供给量变化最多？47共七十八页A C T I V E L E A R N I N G 3: Answers48海滩土地供给(gngj)缺乏弹性PQD1D2SQ1P1ABQ2P2当供给(gngj)缺乏弹性时，需求的增加将导致价格的变化大于数量的变化。 共七十八页A C T I V E L E A R N I N G 3: Answers49汽车(qch)供给富有弹性PQD1D2SQ1P1AQ2P2B当供给富有弹性时，需求的增加将导致(dozh)数量的变化大于价格的变化。共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONS供给价格(jig)弹性如

37、何变化PQ0由于(yuy)生产能力的限制，随数量的增加变的越来越小。$1552512500$31004200elasticity 1elasticity 0.For inferior goods, income elasticity 0 例如：牛肉价格上升导致(dozh)鸡肉的需求量增加。For complements, cross-price elasticity 0 例如：电脑的价格上升将导致软件的需求量下降。共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONCHAPTER SUMMARYElasticity measures the respons

38、iveness of Qd or Qs to one of its determinants. Price elasticity of demand equals percentage change Qd in divided by percentage change in P. When its less than one, demand is “inelastic.” When greater than one, demand is “elastic.” When demand is inelastic, total revenue rises when price rises. When

39、 demand is elastic, total revenue falls when price rises. 共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONCHAPTER SUMMARYDemand is less elastic in the short run, for necessities, for broadly defined goods, or for goods with few close substitutes. Price elasticity of supply equals percentage change in Q

40、s divided by percentage change in P. When its less than one, supply is “inelastic.” When greater than one, supply is “elastic.” Price elasticity of supply is greater in the long run than in the short run. 共七十八页CHAPTER 5 ELASTICITY AND ITS APPLICATIONCHAPTER SUMMARYThe income elasticity of demand mea

41、sures how much quantity demanded responds to changes in buyers incomes. The cross-price elasticity of demand measures how much demand for one good responds to changes in the price of another good. 共七十八页单 项 选 择共七十八页1如果一种物品价格(jig)的微小百分比变动大大减少了该物品的需求量，那么，该物品的需求是 a. 价格缺乏弹性。 b价格富有弹性。 c单位价格弹性。 d收入缺乏弹性。 e收

42、入富有弹性。b共七十八页 2需求价格弹性的定义为a.一种(y zhn)物品价格变动的百分比除以该物品需求量变动的百分比。b收入变动的百分比除以需求量变动的百分比。c一种物品需求量变动的百分比除以该物品价格变动的百分比。d需求量变动的百分比除以收入变动的百分比。 e以上各项都不是。c共七十八页 3一般说来，需求曲线越平坦，越可能的情况是 a价格(jig)富有弹性。 b价格缺乏弹性。 c单位价格弹性。 d以上各项都不对。a共七十八页 4一般来说，供给曲线越陡峭(duqio)，越可能的情况是 a价格富有弹性。 b价格缺乏弹性。 c单位价格弹性。 d以上各项都不对。b共七十八页 5下列哪一种情况会引起

43、一种物品(wpn)的需求曲线是价格缺乏弹性? a. 该物品有大量替代品。 b该物品是低档物品。 c该物品是奢侈品。 d该物品是必需品。d共七十八页 6下列哪一种物品的需求可能是最缺乏价格(jig)弹性的?a.飞机票。B.公共汽车票。c.乘出租汽车。d.交通。d共七十八页 7如果两种物品(wpn)之间的交叉价格弹性是负的，那么，这两种物品(wpn)很可能是 a. 奢侈品。 b必需品。 c互补品。 d替代品。c共七十八页 8如果一种物品的供给曲线是价格富有弹性(tnxng)的，那么a. 供给量对该物品的价格变动是敏感的。b供给量对该物品的价格变动是不敏感的。c需求量对该物品的价格变动是敏感的。d需求量对该物品的价格变动是不敏感的。e以上各项都不对。a共七十八页 9如果一个渔民在鱼腐烂之前要以他能得到的任何一种价格把他当天捕到的