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1、第二章 供给、需求与价格,完全竞争市场模型：The model of demand and supply 价格的作用：信息、激励 价格由供求决定 最优化原则和均衡原则（基本分析框架）(Optimization and Equilibrium) 最优化原则：人们总是试图选择他们能够支付的最好的消费模式。 均衡原则： 市场的供求相互作用使人们需求的数量与供给的数量相等,第二章 供给、需求与价格,2.1 需求与供给 构建模型 （经济现象的简化和抽象化）(Constructing a Model) 市中心住房（房价5000？） 市外环住房（房价固定3000元） 简化：位置 问题：市中心住房如何决定？谁
2、将居住在市中心？配置住房的机制是什么？怎样评价各种配置方案？ 内生变量与外生变量(Exogenous variable and endogenous variable),2.1.1 需求曲线（The Demand Curve ）,价格 保留价格 reservation price：消费者愿意支付的最高价格,数量,5000,4900,4800,1,2,3,4700,数量,价格,D,2.1.1 需求曲线（The Demand Curve ）,个人需求曲线与市场需求曲线 市场需求=个人需求之和 沿着需求曲线的变动 需求曲线移动的原因 收入的变化、替代品价格的变化、互补品价格的变化、人口结构的变化、偏
3、好的变化、信息的变化、获得信贷难易的变化、预期的变化,2.1.1 需求曲线（The Demand Curve ）,需求曲线移动,p,q,2.1.2供给曲线（The Supply Curve）,竞争性市场：多个开放商 时间长短：短期与长期,价格,数量,S,2.1.2供给曲线（The Supply Curve）,一个厂商的供给曲线与市场供给曲线 市场供给=个人供给之和 沿着供给曲线的变动 供给曲线移动的原因 投入品价格的变化、技术的变化、自然环境的变化、获得信贷难易的变化、预期的变化,2.1.3 市场均衡,价格,需求数量,P*,需求曲线D,共给曲线S,均衡价格,Q,均衡数量,Q*,2.1.3 市场
4、均衡,为什么水的价格很低而钻石的价格很高？,2.1.4比较静态分析,P,Q,D,比较静态分析2,P,Q,其他配置方法,完全垄断 一般垄断 租金控制,D,S,供需变动对均衡的影响, Changes in the equilibrium price and quantity in a market are the result of shifts in the supply curve, in the demand curve, or both. An increase in demanda rightward shift of the demand curveincreases both the
5、 equilibrium price and the equilibrium quantity. A decrease in demanda leftward shift of the demand curvepushes down both the equilibrium price and the equilibrium quantity. An increase in supply drives the equilibrium price down but increases the equilibrium quantity. A decrease in supply raises th
6、e equilibrium price but reduces the equilibrium quantity. Often the fluctuations in markets involve shifts of both the supply and demand curves. When they shift in the same direction, the change in quantity is predictable but the change in price is not. When they move in opposite directions, the cha
7、nge in price is predictable but the change in quantity is not. When there are simultaneous shifts of the demand and supply curves, the curve that shifts the greater distance has greater effect on the change in price and quantity.,供需变动对均衡的影响,When demand increases and supply decreases, the price rises
8、 but the change in the quantity is ambiguous. When demand decreases and supply increases, the price falls but the change in the quantity is ambiguous. When both demand and supply increase, the quantity increases but the change in price is ambiguous. When both demand and supply decrease, the quantity
9、 decreases but the change in price is ambiguous.,供需变动对均衡的影响,供需变动对均衡的影响,Case 2,2.1.5帕雷托最优（经济效率）,没有使一个人的状况变好而不使其他人的状况变坏的状态,2.1.6 供求法则,在竞争市场中，价格是由供求法则决定的。需求曲线和供给曲线的移动会导致均衡价格的变化。 恒等式、行为关系和均衡关系,2.2 需求与供给的应用：弹性Elasticity,2.2.1 价格的需求弹性：The price elasticity of demand 需求量变化的百分比除以价格变化的百分比。弹性度量价格变化的敏感程度。,2.2 需
10、求与供给的应用：弹性 Elasticity,2.2.2 弹性大小取决于需求曲线的形状,p1,p2,D1,D2,2.2 需求与供给的应用：弹性 Elasticity,2.2.3 弹性与需求 1 富有弹性 1 缺乏弹性 =1 单位弹性 = 无穷大 =0 无弹性,2.2 需求与供给的应用：弹性 Elasticity,2.2.4 弹性与收入 弹性大于1，降价，收入增加；涨价，收入减少 弹性小于1，降价，收入减少；涨价，收入增加 弹性等于1，降价，涨价，收入不变,2.2 需求与供给的应用：弹性 Elasticity,2.2.5 影响价格弹性的因素： 可替代性、用途的广泛性、对生活的重要程度、占消费支出的
11、比重、时间,2.2 需求与供给的应用：弹性 Elasticity,2.2.6 价格的供给弹性：需求量变化的百分比除以价格变化的百分比。 需求的交叉弹性：一种商品需求量变化的百分比从除以相关产品价格的百分比。 替代-正值 互补-负值 价格的收入弹性：需求量变化的百分比除以收入变化的百分比。 正常品-劣等品：正-负 必须品-奢侈品 收入弹性大于1-收入弹性小于1,弹性,Some Estimated Price Elasticities of Demand Good Price elasticity of demand Inelastic demand Eggs 0.1 Beef 0.4 Stati
12、onery 0.5 Gasoline 0.5 Elastic demand Housing 1.2 Restaurant meals 2.3 Airline travel 2.4 Foreign travel 4.1,弹性,Perfectly Inelastic Demand and Perfectly Elastic Demand ：完全无弹性与完全有弹性,A,B,弹性,收入与弹性：缺乏弹性、单位弹性与富有弹性 If demand for a good is elastic (the price elasticity of demand is greater than 1), an incr
13、ease in price reduces total revenue. In this case, the quantity effect is stronger than the price effect. If demand for a good is inelastic (the price elasticity of demand is less than 1), a higher price increases total revenue. In this case, the price effect is stronger than the quantity effect. If
14、 demand for a good is unit-elastic (the price elasticity of demand is 1), an increase in price does not change total revenue. In this case, the quantity effect and the price effect exactly offset each other.,弹性,When demand is elastic, the quantity effect dominates the price effect; so a fall in pric
15、e increases total revenue. When demand is inelastic, the price effect dominates the quantity effect; so a fall in price reduces total revenue. When demand is unit-elastic, the two effects exactly balance; so a fall in price has no effect on total revenue.,弹性, Demand is perfectly inelastic if it is completely unresponsive to price. It is perfectly elastic if it is infinitely responsive to price. Demand is elastic if the price elasticity of demand is greater than 1; it is inelastic if the price ela
