曼昆经济学原理(微观部分)第5章 弹性及其应用
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Copyright © 2004 South-Western/Thomson Learning
需求弹性
• 需求价格弹性衡量需求量对价格变动的反应程度 • Price elasticity of demand is a measure of how much the quantity demanded of a good responds to a change in the price of that good.
需求价格弹性及其决定因素
• 相近替代品的可获得性 Availability of Close Substitutes • 必需品与奢侈品 Necessities versus Luxuries • 市场的定义 Definition of the Market • 时间的长短 Time Horizon
计算需求的价格弹性
Computing the Price Elasticity of Demand
(100 - 50)
价格 $5
ED
(100 50)/2 (4.00 5.00)/2
(4.00 - 5.00)
4
需求
67 percent -3 - 22 percent
0
50
100 数量
Copyright © 2004 South-Western/Thomson Learning
各种需求曲线
• 因为需求价格弹性衡量需求量对价格变化的 反应，所以它与需求曲线的斜率密切相关。 • Because the price elasticity of demand measures how much quantity demanded responds to the price, it is closely related to the slope of the demand curve.
TR = P x Q
Copyright © 2004 South-Western/Thomson Learning
总收益 价格
$4
P
P × Q = $400 收益
需求
0 Q
100
数量
Copyright © 2004 South-Western/Thomson Learning Copyright©2003 Southwestern/Thomson Learning
Copyright © 2004 South-Western/Thomson Learning
需求价格弹性及其决定因素
• 需求变得更有弹性：
• 相近替代品数量更多 the larger the number of close substitutes. • 是奢侈品 if the good is a luxury. • 更狭窄的市场定义 the more narrowly defined the market. • 时间更长 the longer the time period.
Copyright © 2004 South-Western/Thomson Learning
需求价格弹性的计算
Percentage change in quantity demanded Percentage change in price
Price elasticity of demand =
• 需求量对价格变化的反应不强烈 Quantity demanded does not respond strongly to price changes. 需求价格弹性小于一 • Price elasticity of demand is less than one.
• 富有弹性的需求
Elastic Demand
价格
$5
4 需求 1.价格上升22%
0 2. . . . 使需求量减少22%
80
100
数量
Copyright © 2004 South-Western/Thomson Learning Copyright©2003 Southwestern/Thomson Learning
需求价格弹性
(d) 富有弹性的需求：弹性大于1 价格
Copyright © 2004 South-Western/Thomson Learning
需求的价格弹性
完全无弹性的需求：弹性等于0
价格
$5 4 价格上升 .. 需求
0
2. . . . 需求量不变
100
数量
Copyright © 2004 South-Western/Thomson Learning Copyright©2003 Southwestern/Thomson Learning
• 需求量对价格变化的反应强烈 Quantity demanded responds strongly to changes in price. • 需求价格弹性大于一 Price elasticity of demand is greater than one.
Copyright © 2004 South-Western/Thomson Learning
弹性及其应用
5
Copyright © 2004 South-Western
此文档是曼昆《经济学原理》网授课程的讲义！
最好结合课程进行学习（复制以下链接到浏览器打开）：
http://renren.100xuexi.com/ExamItem/SpecCT.aspx?id=1711d8a8-4e14479d-ba93-bc521f92d415
• 完全有弹性 Perfectly Elastic
• Quantity demanded changes infinitely with any change in price.
• 单位弹性 Unit Elastic
• Quantity demanded changes by the same percentage as the price.
Demand is price elastic
Copyright © 2004 South-Western/Thomson Learning
各种需求曲线
• 完全无弹性 Perfectly Inelastic
• Quantity demanded does not respond to price changes.
Copyright © 2004 South-Western/Thomson Learning
弹性
• 可以让我们更精确地分析供给和需求 … allows us to analyze supply and demand with greater precision. • 是衡量买者和卖者对市场条件变动反应大小 的指标 • … is a measure of how much buyers and sellers respond to changes in market conditions
数量
Copyright © 2004 South-Western/Thomson Learning Copyright©2003 Southwestern/Thomson Learning
沿着一条线性需求曲线的弹性和总收益
• 在一条富有弹性的需求曲线上，价格上升引 起需求量以较大的比例减少。因此，总收益 减少。 • With an elastic demand curve, an increase in the price leads to a decrease in quantity demanded that is proportionately larger. Thus, total revenue decreases.
• 上例中，我们运用中点法计算：
(10 8) 22% (10 8) / 2 2.32 (2.20 2.00) 9.5% (2.00 2.20) / 2
Copyright © 2004 South-Western/Thomson Learning
各种需求曲线
• 缺乏弹性的需求 Inelastic Demand
$5 4 1. 价格上升 22%
需求
0
50
100
数量
2. . . .使需求量减少67%
Copyright © 2004 South-Western/Thomson Learning
需求价格弹性
(e) 完全富有弹性的需求
价格
1. 在任何高于4美元价 格时，需求量为0
$4
需求
2. 在正好为4美元时， 消费者将购买任何一种数量
Copyright © 2004 South-Western/Thomson Learning
当价格变动时总收益如何变动：缺乏弹性的需求
价格
价格从$ 1上升到$3 …
价格
… 引起了总收益从$100到 $240的变化
$3
总收益 = $240 $1 总收益 = $100 0 100 需求
需求
数量
0
80
Copyright © 2004 South-Western/Thomson Learning
需求价格弹性的计算
• 需求价格弹性可以用需 求量变动的百分比除以 价格变动的百分比得到 需求量变动的百分比 ：
需求价格弹性=__________________________
价格变动的百分比
Price elasticity of demand = Percentage change in quantity demanded Percentage change in price
100
中点法：一种更好的计算百分比变动和弹性的 方法
• 计算需求弹性时中点法是一个更好的选择， 因为不管变化的方向如何，它给出的答案是 一样的。 The midpoint formula is preferable when calculating the price elasticity of demand because it gives the same answer regardless of the direction of the change.
0 3. 价格低于4美元时 需求是无限的
数量
Copyright © 2004 South-Western/Thomson Learning
总收益与需求价格弹性
• 总收益是某种物品买者支付的量和卖者得到 的量。 Total revenue is the amount paid by buyers and received by sellers of a good. • 计算：价格乘以销售量得到 Computed as the price of the good times the quantity sold.
沿着一条线性需求曲线的弹性和总收Leabharlann Baidu益
• 在一条缺乏弹性的需求曲线上，价格上升引 起需求量以较小的比例减少。因此，总收益 增加。 • With an inelastic demand curve, an increase in price leads to a decrease in quantity that is proportionately smaller. Thus, total revenue increases.
• 需求价格弹性可以用需求量变动的百分比除以价格 变动的百分比得到。 • Price elasticity of demand is the percentage change in quantity demanded given a percent change in the price.
Copyright © 2004 South-Western/Thomson Learning
(Q2 Q1 ) / [(Q2 Q1 ) / 2] Price elasticity of demand = (P2 P1 ) / [(P2 P1 ) / 2]
Copyright © 2004 South-Western/Thomson Learning
中点法：一种更好的计算百分比变动和弹性的 方法
需求的价格弹性
(b) 缺乏弹性的需求：: 弹性小于 1
价格
$5 1. 4 需求
价格上升22% . . .
0 2. . . . 导致需求数量减少11%
90
100
数量y
Copyright © 2004 South-Western/Thomson Learning
需求价格弹性
(c) 单位弹性需求：弹性等于1
• 例子：如果冰激凌蛋卷的价格从$2上涨到 $2.2,你的购买量从10个下降到8个，那么你 的需求价格弹性是： • (10 8)
20% 10 2 (2.20 2.00) 100 10% 2.00
Copyright © 2004 South-Western/Thomson Learning
需求弹性
• 需求价格弹性衡量需求量对价格变动的反应程度 • Price elasticity of demand is a measure of how much the quantity demanded of a good responds to a change in the price of that good.
需求价格弹性及其决定因素
• 相近替代品的可获得性 Availability of Close Substitutes • 必需品与奢侈品 Necessities versus Luxuries • 市场的定义 Definition of the Market • 时间的长短 Time Horizon
计算需求的价格弹性
Computing the Price Elasticity of Demand
(100 - 50)
价格 $5
ED
(100 50)/2 (4.00 5.00)/2
(4.00 - 5.00)
4
需求
67 percent -3 - 22 percent
0
50
100 数量
Copyright © 2004 South-Western/Thomson Learning
各种需求曲线
• 因为需求价格弹性衡量需求量对价格变化的 反应，所以它与需求曲线的斜率密切相关。 • Because the price elasticity of demand measures how much quantity demanded responds to the price, it is closely related to the slope of the demand curve.
TR = P x Q
Copyright © 2004 South-Western/Thomson Learning
总收益 价格
$4
P
P × Q = $400 收益
需求
0 Q
100
数量
Copyright © 2004 South-Western/Thomson Learning Copyright©2003 Southwestern/Thomson Learning
Copyright © 2004 South-Western/Thomson Learning
需求价格弹性及其决定因素
• 需求变得更有弹性：
• 相近替代品数量更多 the larger the number of close substitutes. • 是奢侈品 if the good is a luxury. • 更狭窄的市场定义 the more narrowly defined the market. • 时间更长 the longer the time period.
Copyright © 2004 South-Western/Thomson Learning
需求价格弹性的计算
Percentage change in quantity demanded Percentage change in price
Price elasticity of demand =
• 需求量对价格变化的反应不强烈 Quantity demanded does not respond strongly to price changes. 需求价格弹性小于一 • Price elasticity of demand is less than one.
• 富有弹性的需求
Elastic Demand
价格
$5
4 需求 1.价格上升22%
0 2. . . . 使需求量减少22%
80
100
数量
Copyright © 2004 South-Western/Thomson Learning Copyright©2003 Southwestern/Thomson Learning
需求价格弹性
(d) 富有弹性的需求：弹性大于1 价格
Copyright © 2004 South-Western/Thomson Learning
需求的价格弹性
完全无弹性的需求：弹性等于0
价格
$5 4 价格上升 .. 需求
0
2. . . . 需求量不变
100
数量
Copyright © 2004 South-Western/Thomson Learning Copyright©2003 Southwestern/Thomson Learning
• 需求量对价格变化的反应强烈 Quantity demanded responds strongly to changes in price. • 需求价格弹性大于一 Price elasticity of demand is greater than one.
Copyright © 2004 South-Western/Thomson Learning
弹性及其应用
5
Copyright © 2004 South-Western
此文档是曼昆《经济学原理》网授课程的讲义！
最好结合课程进行学习（复制以下链接到浏览器打开）：
http://renren.100xuexi.com/ExamItem/SpecCT.aspx?id=1711d8a8-4e14479d-ba93-bc521f92d415
• 完全有弹性 Perfectly Elastic
• Quantity demanded changes infinitely with any change in price.
• 单位弹性 Unit Elastic
• Quantity demanded changes by the same percentage as the price.
Demand is price elastic
Copyright © 2004 South-Western/Thomson Learning
各种需求曲线
• 完全无弹性 Perfectly Inelastic
• Quantity demanded does not respond to price changes.
Copyright © 2004 South-Western/Thomson Learning
弹性
• 可以让我们更精确地分析供给和需求 … allows us to analyze supply and demand with greater precision. • 是衡量买者和卖者对市场条件变动反应大小 的指标 • … is a measure of how much buyers and sellers respond to changes in market conditions
数量
Copyright © 2004 South-Western/Thomson Learning Copyright©2003 Southwestern/Thomson Learning
沿着一条线性需求曲线的弹性和总收益
• 在一条富有弹性的需求曲线上，价格上升引 起需求量以较大的比例减少。因此，总收益 减少。 • With an elastic demand curve, an increase in the price leads to a decrease in quantity demanded that is proportionately larger. Thus, total revenue decreases.
• 上例中，我们运用中点法计算：
(10 8) 22% (10 8) / 2 2.32 (2.20 2.00) 9.5% (2.00 2.20) / 2
Copyright © 2004 South-Western/Thomson Learning
各种需求曲线
• 缺乏弹性的需求 Inelastic Demand
$5 4 1. 价格上升 22%
需求
0
50
100
数量
2. . . .使需求量减少67%
Copyright © 2004 South-Western/Thomson Learning
需求价格弹性
(e) 完全富有弹性的需求
价格
1. 在任何高于4美元价 格时，需求量为0
$4
需求
2. 在正好为4美元时， 消费者将购买任何一种数量
Copyright © 2004 South-Western/Thomson Learning
当价格变动时总收益如何变动：缺乏弹性的需求
价格
价格从$ 1上升到$3 …
价格
… 引起了总收益从$100到 $240的变化
$3
总收益 = $240 $1 总收益 = $100 0 100 需求
需求
数量
0
80
Copyright © 2004 South-Western/Thomson Learning
需求价格弹性的计算
• 需求价格弹性可以用需 求量变动的百分比除以 价格变动的百分比得到 需求量变动的百分比 ：
需求价格弹性=__________________________
价格变动的百分比
Price elasticity of demand = Percentage change in quantity demanded Percentage change in price
100
中点法：一种更好的计算百分比变动和弹性的 方法
• 计算需求弹性时中点法是一个更好的选择， 因为不管变化的方向如何，它给出的答案是 一样的。 The midpoint formula is preferable when calculating the price elasticity of demand because it gives the same answer regardless of the direction of the change.
0 3. 价格低于4美元时 需求是无限的
数量
Copyright © 2004 South-Western/Thomson Learning
总收益与需求价格弹性
• 总收益是某种物品买者支付的量和卖者得到 的量。 Total revenue is the amount paid by buyers and received by sellers of a good. • 计算：价格乘以销售量得到 Computed as the price of the good times the quantity sold.
沿着一条线性需求曲线的弹性和总收Leabharlann Baidu益
• 在一条缺乏弹性的需求曲线上，价格上升引 起需求量以较小的比例减少。因此，总收益 增加。 • With an inelastic demand curve, an increase in price leads to a decrease in quantity that is proportionately smaller. Thus, total revenue increases.
• 需求价格弹性可以用需求量变动的百分比除以价格 变动的百分比得到。 • Price elasticity of demand is the percentage change in quantity demanded given a percent change in the price.
Copyright © 2004 South-Western/Thomson Learning
(Q2 Q1 ) / [(Q2 Q1 ) / 2] Price elasticity of demand = (P2 P1 ) / [(P2 P1 ) / 2]
Copyright © 2004 South-Western/Thomson Learning
中点法：一种更好的计算百分比变动和弹性的 方法
需求的价格弹性
(b) 缺乏弹性的需求：: 弹性小于 1
价格
$5 1. 4 需求
价格上升22% . . .
0 2. . . . 导致需求数量减少11%
90
100
数量y
Copyright © 2004 South-Western/Thomson Learning
需求价格弹性
(c) 单位弹性需求：弹性等于1
• 例子：如果冰激凌蛋卷的价格从$2上涨到 $2.2,你的购买量从10个下降到8个，那么你 的需求价格弹性是： • (10 8)
20% 10 2 (2.20 2.00) 100 10% 2.00
Copyright © 2004 South-Western/Thomson Learning