微觀經濟理論3Elasticitytheory課件

1、Chapter 3 Elasticity Theory1The contents of the chapter 1.What is elasticity? 2. Elasticity of Demand 3. Elasticity of Supply21.What is elasticity?彈性elasticity： 自變量變動一個百分比所引起的因變量變動的百分比。(注意：不是因變量變動量與自變量變動量之比。) e= （ Y/Y）/（ X/X）=（Y/ X）（ X/Y ） 彈性是一個具體的數值coefficient，與變量之間的度量無關。為什么用彈性： 通過彈性，可以表示存在函數關系的變量與

2、變量之間反應的敏感程度并做出量化分析，從而能更好地認識變量之間的相互關系。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彈性公式Elasticity formula弧彈性公式arc elasticity formula: Q PaEd=- (a點到b點的彈性) P Qa Q PbEd=- (b點到a點的彈性) P Qb9弧彈性公式(中點公式) Q/（

6、Qa+Qb）/2 Q Pa+Pb Ed = - 或 =- P/（Pa+Pb）/2 P Qa+Qb點彈性公式與計算 dQ/Q dQ P Ed =- 或 = - dP/P dP Q10E.G.某雜志價格為2元時銷售量為5萬冊，價格為3元時銷售量為3萬冊，則需求價格彈性為多少？解：價格從2元上漲至3元，Ed= 0.8 價格從3元下降至2元，Ed= 2 利用中點公式計算則有Ed=1.2511需求函數：Qd =a-bP (a、b為常數，b0)，設P=1，求點彈性。 解：P=1，則Qd = a - b 1，另dQ/dP= -b dQ P 1 b Ed = - = b = dP Q a b a b12需求的

7、價格弧彈性分類The classification of price elasticity of demand Ed=0，需求完全無彈性Perfectly inelastic 0|Ed|1，需求缺乏彈性inelastic |Ed|=1，需求具有單位彈性unit elastic 1|Ed|1中點C： |Ed|=1線段CB： |Ed|1, elastic，so dTR/dP0, P TREd0, P TR Ed=1,unit elastic， dTR/dP=0,no affectEd=0，perfectly inelastic收入同比例于價格變化而變化。Ed=，perfectly elastic既

8、定價格下收益可無限增加，廠商不會降價，漲價則會使收入減少為20影響需求價格彈性的因素The factors that affect the price elasticity of demand商品的可替代性 Substitutability of goods商品用途的廣泛性 Extensive use of goods商品對消費者的重要程度(preferrence) Importance of goods to consumers商品的消費支出在消費總支出中所占的比重 The proportion of consumer spending in the consumer goods in to

9、tal expenditure消費者調節(jié)需求量的時間 Time for consumer demand 21需求收入彈性 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需求交叉彈性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，供給完全無彈性perfectly inelastic0Es1，供給缺乏彈性inelasticEs=1，供給具有單位彈性unit elastic1Es，供給富有彈性elasticEs=，供給有無限彈性 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谷賤傷農 The lower price of food will reduce the revenue of farmers稅負分擔理論 The theory of tax burden蛛網理論 Spider-we

13、b theory35谷賤傷農QopE1P1Q1E2P2Q2FDS1S236稅負分擔理論oQPS0E0P0Q0D0S1E1P1Q1P2tD0E1P1Q1P2彈性不同稅收的分擔也不同37蛛網模型基本假設： (1)本期的供給量取決于上期的價格； (2)本期的需求量取決于本期的價格。三種類型：收斂型蛛網、發(fā)散型蛛網、穩(wěn)定型蛛網適用分析對象：有生產周期的產品。38蛛網模型（數學方法）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將上式正規(guī)化，得Pt +1+（b/d）Pt=（a+c）/b39蛛網模型（數

14、學方法）解上差分方程：Pt=P0-(a+c)/(b+d)(-d/b)t+ (a+c)/(b+d)P0表示初始價格在市場均衡時， Pe = Pt = Pt +1因此有： Pe= (a+c)/(b+d)，將Pe代入解中，Pt=（P0 Pe ） (-d/b)t+ Pe40蛛網模型（數學方法）通過上式子，可以看出：1.當db時，震蕩將為放大震蕩2.當d=b時，震蕩為單位震蕩3.當d0)Qst=-c+dPt-1 Pt-1 =c/d+(1/d) Qst (c,d0)41收斂型蛛網（圖示）oQPEDSP*Q*P0Q1P1Q2P2Q3P3Q442發(fā)散型蛛網（圖示）oQPEDSP*Q*P0Q1P1Q2P2Q3P