《中级微观经济学》pr8e-ch04ly

Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. * of 50 4.1 Individual Demand4.2 Income and Substitution Effects4.3 Market Demand4.4 Consumer Surplus4.5 Network Externalities4.6 Empirical Estimation of DemandAppendix: Demand TheoryA Mathematical TreatmentC H A P T E R 4 Prepared by:Fernando Quijano, Illustrator Individual and Market Demand个人需求和市场需求CHAPTER OUTLINE 2 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. 4.1 个人需求4.2 收入效应和替代效应4.3 市场需求4.4 消费者剩余4.5 网络外部性4.6 需求的经验估计 3 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. Individual Demand 价格变化的效应4.1 FIGURE 4.1 收入和衣服价格保持不变，而食物价格下降， 4 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. price-consumption curve 价格消费曲线 勾画了与食物每一种可能的价格相对应的效用最大化的食物和衣服组合 individual demand curve 个人需求曲线 把单一的消费者将会购买的商品数量和该商品的价格联系起来The Individual Demand CurveThe individual demand curve has two important properties:1. The level of utility that can be attained changes as we move along the curve. 2. At every point on the demand curve, the consumer is maximizing utility by satisfying the condition that the marginal rate of substitution (MRS) of food for clothing equals the ratio of the prices of food and clothing. 5 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. Income Changes收入变化 保持所有商品的价格不变，消费者的收入增加会引起其对市场篮子的选择的改变。 income-consumption curve 6 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. EFFECT OF INCOME CHANGES需求曲线因收入增加而向右的移动如（b）图所示（点E、G和H分别对应于点A、B和D） 7 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. Normal versus Inferior Goods正常商品和劣质商品收入增加时，消费量反而减少。 8 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. Engel curve 恩格尔曲线 将一种商品的消费量和收入联系起来的曲线. 9 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. 替代品和互补品两种商品，如果一种商品价格的上涨导致另一种商品需求量上升，那么这两种商品互为替代品。两种商品，如果一种商品价格的上涨导致另一种商品需求量下降，那么这两种商品互为替代品。两种商品，如果一种商品价格的变化对另一种商品需求量没有影响，那么这两种商品是独立的。The fact that goods can be complements or substitutes suggests that when studying the effects of price changes in one market, it may be important to look at the consequences in related markets. 10 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. 收入效应和替代效应4.2一种商品价格的下跌有两种效应： 消费者往往会更多的购买变得便宜的商品，而减少购买那些变得相对较贵的商品。 因为其中的一种商品变得便宜了，消费者的实际购买力得到了提高。 11 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. A decrease in the price of food has both an income effect and a substitution effect. FIGURE 4.6Total Effect = Substitution Effect +Income Effect 12 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. INFERIOR GOOD 13 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. 收入效应和替代效应4.2当食物是一种劣质商品，而收入效应又大到足以支配替代效应时，需求曲线就会向上倾斜。消费者原先位于A点，但在食物价格下跌后，消费者移至B点，减少了事物的消费。吉芬商品 这种商品的收入效应可能足够大，使得它的需求曲线向上倾斜。衣服（单位/月） 食物（单位/月） 替代效应收入效应总效应 14 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. market demand curve Curve relating the quantity of a goodthat all consumers in a market will buy to its price.Market Demand4.3TABLE 4.2 DETERMINING THE MARKET DEMAND CURVE(1)PRICE($) (2)INDIVIDUAL A(UNITS) (3)INDIVIDUAL B(UNITS) (4)INDIVIDUAL C(UNITS) (5)MARKET UNITS1 6 10 16 322 4 8 13 253 2 6 10 18 4 0 4 7 115 0 2 4 6From Individual to Market Demand 15 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. 市场需求4.3 市场需求曲线 当商品的价格变化时，全部消费者总共愿意购买的商品数量。表4.2 确定市场需求曲线 (1) (2) (3) (4) (5)价格个体l A个体 B个体 C市场(美元) (单位) （单位) (单位) (单位) 1 6 10 16 32 2 4 8 13 25 3 2 6 10 18 4 0 4 7 11 5 0 2 4 6 16 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. SUMMING TO OBTAIN A MARKET DEMAND CURVE 17 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. 市场需求4.3需求的弹性将商品的数量记作Q，其价格记作P，需求的价格弹性为：(4.1)当需求缺乏弹性（即Ep 的绝对值小于1)时,需求量对于价格变化的反应就相对迟钝些。结果，当价格上涨时，花在该产品上的总支出也增加了。当需求富有弹性时（ E p 的绝对值大于1），若价格上升，花在该产品上的总支出就会下降。mathamatics 18 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. 市场需求4.3不变弹性的需求曲线 沿着需求曲线，需求的价格弹性为常数。单位弹性需求曲线如果在任一价格下需求的价格弹性都为1.0，那么沿着需求曲线D的总支出保持不变。电影票的 价格（美元） 电影票数量（千张） 19 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. consumer surplus消费者剩余 =消费者愿意付出的-实际支出的Difference between what a consumer is willing to pay for a good and the amount actually paid.Consumer Surplus消费者剩余 4.4 20 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. 21 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. Empirical Estimation of Demand4.6 TABLE 4.6 DEMAND DATAYEAR QUANTITY (Q) PRICE (P) INCOME (I)2004 4 24 102005 7 20 102006 8 17 102007 13 17 172008 16 10 27 2009 15 15 272010 19 12 202011 20 9 202012 22 5 20 (4.2)Using the data in the table and the least squares method, the demand relationship is: 22 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. Appendix to Chapter 4Demand TheoryA Mathematical TreatmentSuppose, for example, that Bobs utility function is given by U(X, Y) = log X +log Y, where X is used to represent food and Y represents clothing. In that case, the marginal utility associated with the additional consumption of X is given by the partial derivative of the utility function with respect to good X. Here, MUX, representing the marginal utility of good X, is given byUtility Maximization The consumers optimization problem may be written as (A4.1)subject to the constraint that all income is spent on the two goods: (A4.2) 23 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. 1. Stating the Problem First, we write the Lagrangian for the problem.The Method of Lagrange Multipliers Note that we have written the budget constraint as (A4.3)method of Lagrange multipliersTechnique to maximize or minimize a function subject to one or more constraints. Lagrangian Function to be maximized or minimized, plus avariable (the Lagrange multiplier) multiplied by the constraint. 24 of 50Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e. 2. Differentiating the Lagrangian We choose values of X and Y that satisfy the budget constraint, then the second term in equation (A4.3) will be zero. By differentiating with respect to X, Y, and l and then equating the derivatives to zero, we can obtain the necessary conditions for a maximum. (A4.4)3. Solving the Resulting Equations The three equations in (A4.4) can be rewritten as