微观经济理论3Elasticitytheory课件

1、Chapter 3 Elasticity Theory1The contents of the chapter 1.What is elasticity? 2. Elasticity of Demand 3. Elasticity of Supply21.What is elasticity?弹性elasticity： 自变量变动一个百分比所引起的因变量变动的百分比。(注意：不是因变量变动量与自变量变动量之比。) e= （ Y/Y）/（ X/X）=（Y/ X）（ X/Y ） 弹性是一个具体的数值coefficient，与变量之间的度量无关。为什么用弹性： 通过弹性，可以表示存在函数关系的变量与

2、变量之间反应的敏感程度并做出量化分析，从而能更好地认识变量之间的相互关系。3Elasticity is a measure of responsiveness. Two words are important here. The word measure means that elasticity results are reported as numbers, or elasticity coefficients. The word responsiveness means that there is a stimulus-reaction involved. Some change or

3、stimulus causes people to react by changing their behavior, and elasticity measures the extent to which people react. 42. Elasticity of Demand Qd=f( P, I, Pi,Pe) 52.1 Price elasticity of demandThe most common elasticity measurement is that of price elasticity of demand. It measures how much consumer

4、s respond in their buying decisions to a change in price.6The basic formula used to determine price elasticity is: 7E.G. If price increases by 10% and consumers respond by decreasing purchases by 20%, the equation computes the elasticity coefficient as -2. The result is negative because an increase

5、in price (a positive number) leads to a decrease in purchases (a negative number). Because the law of demand says it will always be negative, many economists ignore the negative sign.8弹性公式Elasticity formula弧弹性公式arc elasticity formula: Q PaEd=- (a点到b点的弹性) P Qa Q PbEd=- (b点到a点的弹性) P Qb9弧弹性公式(中点公式) Q/（

6、Qa+Qb）/2 Q Pa+Pb Ed = - 或 =- P/（Pa+Pb）/2 P Qa+Qb点弹性公式与计算 dQ/Q dQ P Ed =- 或 = - dP/P dP Q10E.G.某杂志价格为2元时销售量为5万册，价格为3元时销售量为3万册，则需求价格弹性为多少？解：价格从2元上涨至3元，Ed= 0.8 价格从3元下降至2元，Ed= 2 利用中点公式计算则有Ed=1.2511需求函数：Qd =a-bP (a、b为常数，b0)，设P=1，求点弹性。 解：P=1，则Qd = a - b 1，另dQ/dP= -b dQ P 1 b Ed = - = b = dP Q a b a b12需求的

7、价格弧弹性分类The classification of price elasticity of demand Ed=0，需求完全无弹性Perfectly inelastic 0|Ed|1，需求缺乏弹性inelastic |Ed|=1，需求具有单位弹性unit elastic 1|Ed|1中点C： |Ed|=1线段CB： |Ed|1, elastic，so dTR/dP0, P TREd0, P TR Ed=1,unit elastic， dTR/dP=0,no affectEd=0，perfectly inelastic收入同比例于价格变化而变化。Ed=，perfectly elastic既

8、定价格下收益可无限增加，厂商不会降价，涨价则会使收入减少为20影响需求价格弹性的因素The factors that affect the price elasticity of demand商品的可替代性 Substitutability of goods商品用途的广泛性 Extensive use of goods商品对消费者的重要程度(preferrence) Importance of goods to consumers商品的消费支出在消费总支出中所占的比重 The proportion of consumer spending in the consumer goods in to

9、tal expenditure消费者调节需求量的时间 Time for consumer demand 21需求收入弹性 Income elasticity of demandIt measures how the quantity demanded changes as consumer income changes.It is calculated as: Percentage change in quantity demandedEi= Percentage change in income22formula： Q/Q Q I Ei = 或 = I/I I QClassify： Ey0,

10、Normal, good; Ey0，inferior good 0 Ey1， Luxury23需求交叉弹性Cross-price elasticity of demandDefinition：It measures how the quantity demanded of one good changes as the price of another good changes.It is calculated as : Percentage change in quantity of good x Exy= Percentage change in the price of good y24

11、Formula： Qy/Qy Qy Px Exy = or = Px/Px Px QyClassification： Exy0，Substitute 替代品； Exy0)，P=1，then the point Es will be ? P=1，Qs = c+d，dQ/dP= d dQ P 1 d Es = = d = dP Q c+d c+d31Classification Es=0，供给完全无弹性perfectly inelastic0Es1，供给缺乏弹性inelasticEs=1，供给具有单位弹性unit elastic1Es，供给富有弹性elasticEs=，供给有无限弹性 perfec

12、tly elastic32Classification for EsOPQS1 Es=0S5 Es=S3 Es=1S2 Es133The factors affecting EsTime for producer adjusting yeildMarginal costProduction cycle344.The applications of elasticity theory谷贱伤农 The lower price of food will reduce the revenue of farmers税负分担理论 The theory of tax burden蛛网理论 Spider-we

13、b theory35谷贱伤农QopE1P1Q1E2P2Q2FDS1S236税负分担理论oQPS0E0P0Q0D0S1E1P1Q1P2tD0E1P1Q1P2弹性不同税收的分担也不同37蛛网模型基本假设： (1)本期的供给量取决于上期的价格； (2)本期的需求量取决于本期的价格。三种类型：收敛型蛛网、发散型蛛网、稳定型蛛网适用分析对象：有生产周期的产品。38蛛网模型（数学方法）1.Qdt=Qst 2.Qdt=a-bPt (a,b0)3.Qst=-c+dPt-1 (c,d0)由1、2、3可得：bPt + dPt-1 +=a+c将上式正规化，得Pt +1+（b/d）Pt=（a+c）/b39蛛网模型（数

14、学方法）解上差分方程：Pt=P0-(a+c)/(b+d)(-d/b)t+ (a+c)/(b+d)P0表示初始价格在市场均衡时， Pe = Pt = Pt +1因此有： Pe= (a+c)/(b+d)，将Pe代入解中，Pt=（P0 Pe ） (-d/b)t+ Pe40蛛网模型（数学方法）通过上式子，可以看出：1.当db时，震荡将为放大震荡2.当d=b时，震荡为单位震荡3.当d0)Qst=-c+dPt-1 Pt-1 =c/d+(1/d) Qst (c,d0)41收敛型蛛网（图示）oQPEDSP*Q*P0Q1P1Q2P2Q3P3Q442发散型蛛网（图示）oQPEDSP*Q*P0Q1P1Q2P2Q3P