微觀經(jīng)濟(jì)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(dòng)一個(gè)百分比所引起的因變量變動(dòng)的百分比。(注意：不是因變量變動(dòng)量與自變量變動(dòng)量之比。) e= （ Y/Y）/（ X/X）=（Y/ X）（ X/Y ） 彈性是一個(gè)具體的數(shù)值coefficient，與變量之間的度量無關(guān)。為什么用彈性： 通過彈性，可以表示存在函數(shù)關(guān)系的變量與

2、變量之間反應(yīng)的敏感程度并做出量化分析，從而能更好地認(rèn)識(shí)變量之間的相互關(guān)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(diǎn)到b點(diǎn)的彈性) P Qa Q PbEd=- (b點(diǎn)到a點(diǎn)的彈性) P Qb9弧彈性公式(中點(diǎn)公式) Q/（

6、Qa+Qb）/2 Q Pa+Pb Ed = - 或 =- P/（Pa+Pb）/2 P Qa+Qb點(diǎn)彈性公式與計(jì)算 dQ/Q dQ P Ed =- 或 = - dP/P dP Q10E.G.某雜志價(jià)格為2元時(shí)銷售量為5萬冊(cè)，價(jià)格為3元時(shí)銷售量為3萬冊(cè)，則需求價(jià)格彈性為多少？解：價(jià)格從2元上漲至3元，Ed= 0.8 價(jià)格從3元下降至2元，Ed= 2 利用中點(diǎn)公式計(jì)算則有Ed=1.2511需求函數(shù)：Qd =a-bP (a、b為常數(shù)，b0)，設(shè)P=1，求點(diǎn)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(jià)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u(píng)nit elastic 1|Ed|1中點(diǎn)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(jià)格變化而變化。Ed=，perfectly elastic既

8、定價(jià)格下收益可無限增加，廠商不會(huì)降價(jià)，漲價(jià)則會(huì)使收入減少為20影響需求價(jià)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(duì)消費(fèi)者的重要程度(preferrence) Importance of goods to consumers商品的消費(fèi)支出在消費(fèi)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(fèi)者調(diào)節(jié)需求量的時(shí)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u(píng)nit 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(nóng) The lower price of food will reduce the revenue of farmers稅負(fù)分擔(dān)理論 The theory of tax burden蛛網(wǎng)理論 Spider-we

13、b theory35谷賤傷農(nóng)QopE1P1Q1E2P2Q2FDS1S236稅負(fù)分擔(dān)理論oQPS0E0P0Q0D0S1E1P1Q1P2tD0E1P1Q1P2彈性不同稅收的分擔(dān)也不同37蛛網(wǎng)模型基本假設(shè)： (1)本期的供給量取決于上期的價(jià)格； (2)本期的需求量取決于本期的價(jià)格。三種類型：收斂型蛛網(wǎng)、發(fā)散型蛛網(wǎng)、穩(wěn)定型蛛網(wǎng)適用分析對(duì)象：有生產(chǎn)周期的產(chǎn)品。38蛛網(wǎng)模型（數(shù)學(xué)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(wǎng)模型（數(shù)

14、學(xué)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(jià)格在市場(chǎng)均衡時(shí)， 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(wǎng)模型（數(shù)學(xué)方法）通過上式子，可以看出：1.當(dāng)db時(shí)，震蕩將為放大震蕩2.當(dāng)d=b時(shí)，震蕩為單位震蕩3.當(dāng)d0)Qst=-c+dPt-1 Pt-1 =c/d+(1/d) Qst (c,d0)41收斂型蛛網(wǎng)（圖示）oQPEDSP*Q*P0Q1P1Q2P2Q3P3Q442發(fā)散型蛛網(wǎng)（圖示）oQPEDSP*Q*P0Q1P1Q2P2Q3P