《中级微观经济学》pr8e_ch04ly.ppt

Copyright 2013 Pearson Education, Inc. Microeconomics Pindyck/Rubinfeld, 8e.,* of 50,4.1 Individual Demand 4.2 Income and Substitution Effects 4.3 Market Demand 4.4 Consumer Surplus 4.5 Network Externalities 4.6 Empirical Estimation of Demand Appendix: Demand TheoryA Mathematical Treatment,C 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,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,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，, 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 Curve,The 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.,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,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）,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。, 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.,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.,收入效应和替代效应,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。,A decrease in the price of food has both an income effect and a substitution effect.,FIGURE 4.6,Total Effect = Substitution Effect +Income Effect,INFERIOR GOOD,收入效应和替代效应,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, market demand curve Curve relating the quantity of a good that all consumers in a market will buy to its price.,Market Demand,4.3,From Individual to Market Demand,市场需求,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,SUMMING TO OBTAIN A MARKET DEMAND CURVE,市场需求,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（ Ep 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,市场需求,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）, 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,Empirical Estimation of Demand,4.6,(4.2),Using the data in the table and the least squares method, the demand relationship is:,Appendix to Chapter 4 Demand TheoryA Mathematical Treatment,Suppose, 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 by,Utility 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),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 multipliers Technique to maximize or minimize a function subject to one or more constraints., Lagrangian Function to be maximized or minimized, plus a variable (the Lagrange multiplier) multiplied by the constraint.,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 differentiati