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1、中级微观经济 学15Chapter FifteenMarket Demand 市场需求StructureuFrom Individual to Market Demand FunctionsuElasticitiesuRevenue and own-price elasticity of demanduMarginal revenue and price elasticityFrom Individual to Market Demand FunctionsuThink of an economy containing n consumers, denoted by i = 1, ,n.uCo
2、nsumer is ordinary demand function for commodity j isFrom Individual to Market Demand FunctionsuWhen all consumers are price- takers, the market demand function for commodity j isuIf all consumers are identical then where M = nm.From Individual to Market Demand FunctionsuThe market demand curve is t
3、he “horizontal sum” of the individual consumers demand curves.uE.g. suppose there are only two consumers; i = A,B.From Individual to Market Demand Functions p1p12015p1 p1”p1 p1”From Individual to Market Demand Functions p1p1p12015p1 p1”p1 p1”p1From Individual to Market Demand Functions p1p1p12015p1
4、p1”p1 p1”p1 p1”From Individual to Market Demand Functions p1p1p1201535p1 p1”p1 p1”p1 p1”The “horizontal sum” of the demand curves of individuals A and B.Elasticities （弹性）uElasticity measures the “sensitivity” of one variable with respect to another.uThe elasticity of variable X with respect to varia
5、ble Y isEconomic Applications of ElasticityuEconomists use elasticities to measure the sensitivity of lquantity demanded of commodity i with respect to the price of commodity i (own-price elasticity of demand，需求的自价格弹性) ldemand for commodity i with respect to the price of commodity j (cross-price ela
6、sticity of demand， 需求的交叉价格弹性). Economic Applications of Elasticityldemand for commodity i with respect to income (income elasticity of demand 需求的收入弹 性) lquantity supplied of commodity i with respect to the price of commodity i (own-price elasticity of supply 供给的自价格弹性)Economic Applications of Elastic
7、itylquantity supplied of commodity i with respect to the wage rate (elasticity of supply with respect to the price of labor) land many, many others.Own-Price Elasticity of DemanduQ: Why not use a demand curves slope to measure the sensitivity of quantity demanded to a change in a commoditys own pric
8、e?Own-Price Elasticity of DemandX1*5501010slope = - 2slope = - 0.2p1p1In which case is the quantity demanded X1* more sensitive to changes to p1?X1*Own-Price Elasticity of Demand5501010slope = - 2slope = - 0.2p1p1X1*X1*In which case is the quantity demanded X1* more sensitive to changes to p1?Own-Pr
9、ice Elasticity of Demand5501010slope = - 2slope = - 0.2p1p110-packsSingle UnitsX1*X1*In which case is the quantity demanded X1* more sensitive to changes to p1?Own-Price Elasticity of Demand5501010slope = - 2slope = - 0.2p1p110-packsSingle UnitsX1*X1*In which case is the quantity demanded X1* more s
10、ensitive to changes to p1? It is the same in both cases.Own-Price Elasticity of DemanduQ: Why not just use the slope of a demand curve to measure the sensitivity of quantity demanded to a change in a commoditys own price?uA: Because the value of sensitivity then depends upon the (arbitrary) units of
11、 measurement used for quantity demanded. Own-Price Elasticity of Demandis a ratio of percentages and so has no units of measurement. Hence own-price elasticity of demand is a sensitivity measure that is independent of units of measurement.Point Own-Price ElasticityE.g. Suppose pi = a - bXi. Then Xi
12、= (a-pi)/b andTherefore,Point Own-Price ElasticitypiXi*pi = a - bXi*aa/bPoint Own-Price ElasticitypiXi*pi = a - bXi*aa/bPoint Own-Price ElasticitypiXi*pi = a - bXi*aa/bPoint Own-Price ElasticitypiXi*pi = a - bXi*aa/bPoint Own-Price ElasticitypiXi*api = a - bXi*a/bPoint Own-Price ElasticitypiXi*api =
13、 a - bXi*a/ba/2a/2bPoint Own-Price ElasticitypiXi*api = a - bXi*a/ba/2a/2bPoint Own-Price ElasticitypiXi*api = a - bXi*a/ba/2a/2bPoint Own-Price ElasticitypiXi*api = a - bXi*a/ba/2a/2bown-price elastic （有弹性）own-price inelastic （缺乏弹性）Point Own-Price ElasticitypiXi*api = a - bXi*a/ba/2a/2bown-price el
14、asticown-price inelastic(own-price unit elastic) 单位弹性Point Own-Price ElasticityE.g. ThensoPoint Own-Price ElasticitypiXi*everywhere along the demand curve.Revenue and Own-Price Elasticity of DemanduIf raising a commoditys price causes little decrease in quantity demanded, then sellers revenues rise.
15、 lHence own-price inelastic demand causes sellers revenues to rise as price rises.uIf raising a commoditys price causes a large decrease in quantity demanded, then sellers revenues fall. lHence own-price elastic demand causes sellers revenues to fall as price rises.Revenue and Own-Price Elasticity o
16、f DemandSellers revenue isRevenue and Own-Price Elasticity of DemandSellers revenue isSoRevenue and Own-Price Elasticity of DemandSellers revenue isSoRevenue and Own-Price Elasticity of DemandSellers revenue isSoRevenue and Own-Price Elasticity of DemandRevenue and Own-Price Elasticity of Demandso ifthenand a change to price does not alter sellers revenue.Revenue and Own-Price Elasticity of Demandbut ifthe
