Elasticity and Its
Application
弹性及其应用
Chapter 5
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Elasticity . . . 弹性…
u … is a measure of how much buyers
and sellers respond to changes in market
conditions.
…是衡量买者和卖者对市场条件变动的
反应大小的指标。
u … allows us to analyze supply and
demand with greater precision.
…使我们可以更精确地分析供给与需求
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Price Elasticity of Demand
u Price elasticity of demand is the
percentage change in quantity demanded
given a percent change in the price.
u It is a measure of how much the quantity
demanded of a good responds to a change
in the price of that good.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
需求的价格弹性
u 需求的价格弹性——价格变化1%引起
的需求量的变化百分比值。
u 它是一种物品的需求量对其价格变动
的反应程度的衡量。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Determinants of Price Elasticity of Demand
需求价格弹性的决定因素
u Necessities versus Luxuries
必需品与奢侈品
u Availability of Close Substitutes
相近替代品的可获得性
u Definition of the Market 市场的定义
u Time Horizon 时间的长短
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Determinants of
Price Elasticity of Demand
Demand tends to be more elastic :
n if the good is a luxury.
n the longer the time period.
n the larger the number of close
substitutes.
n the more narrowly defined the market.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
价格需求弹性的决定因素
需求倾向于富有弹性：
n 如果物品是奢侈品
n 时期更长
n 相近替代品的数量更多
n 市场定义的范围更窄
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Computing the Price Elasticity of Demand
The price elasticity of demand is computed
as the percentage change in the quantity
demanded divided by the percentage
change in price.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
计算需求价格弹性
用需求量变动的百分比除以价格变动的百
分比来计算需求价格弹性。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Computing the Price Elasticity of Demand
Example: If the price of an ice cream cone increases
from $ to $ and the amount you buy falls from
10 to 8 cones then your elasticity of demand would be
calculated as:
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
计算需求价格弹性
例子: 如果冰激凌蛋卷的价格从2美元上升到
美元，你的购买量从10个下降到8个，你的
需求价格弹性计算如下：
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
The Midpoint Method: A Better Way to Calculate
Percentage Changes and Elasticities
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.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
中点法:一种计算百分比变化
和弹性的更好方法
中点法 是计算需求价格弹性的更好方法，因
为无论变动的方向如何，中点法给出了同一
个答案。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
The Midpoint Method: A Better Way to Calculate
Percentage Changes and Elasticities
Example: If the price of an ice cream cone increases
from $ to $ and the amount you buy falls from
10 to 8 cones the your elasticity of demand, using the
midpoint formula, would be calculated as:
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
中点法:一种计算百分比变化和弹性的更好方法
例子:如果冰激凌蛋卷的价格从2美元上升到
美元，你的购买量从10个下降到8个，利用中
点法你的需求价格弹性计算如下：
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
The Variety of Demand Curves
Inelastic Demand
u Quantity demanded does not respond strongly
to price changes.
u Price elasticity of demand is less than one.
Elastic Demand
u Quantity demanded responds strongly to
changes in price.
u Price elasticity of demand is greater than one.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
多种需求曲线
缺乏弹性的需求
u需求量不随着价格变化而强烈变化。
u需求价格弹性小于1。
富有弹性的需求
u需求量随着价格变化而强烈变化。
u需求价格弹性大于1。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Computing the Price Elasticity of Demand
计算需求的价格弹性
Demand is price elastic
需求富有弹性
$5
4 Demand
需求
Quantity
数量
1000
Price
价格
50
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
The Variety of Demand Curves
u Perfectly Inelastic
Quantity demanded does not respond to
price changes.
u Perfectly Elastic
Quantity demanded changes infinitely
with any change in price.
u Unit Elastic
Quantity demanded changes by the same
percentage as the price.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
多种需求曲线
u 完全无弹性
需求量不随价格变化而变化。
u 完全弹性
价格极小变化引起需求量极大变动。
u 单位弹性
需求量与价格同比例变动。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
A Variety of Demand Curves
多种需求弹性曲线
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.
由于需求的价格弹性衡量需求量对价格变化的反应
程度，所以它与需求曲线的斜率密切相关。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Perfectly Inelastic Demand— Elasticity equals 0
完全无弹性的需求——弹性等于0
Quantity 数量
Price
价格
4
$5
Demand 需求
100
2. ...leaves the quantity demanded unchanged.
2….需求量不变。
1. An
increase
in price...
1.价格上
升…
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Inelastic Demand—— Elasticity is less than 1
缺乏弹性的需求——弹性小于1
Quantity 数量
Price
价格
4
$51. A 22%
increase
in price...
1.价格上升
22％… Demand 需求
10090
2. ...leads to a 11% decrease in quantity.
2….使需求量减少11%。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Unit Elastic Demand—— Elasticity equals 1
单位需求弹性——弹性等于1
Quantity 数量
Price
价格
4
$51. A 22%
increase
in price...
1.价格上升
22％… Demand 需求
10080
2. ...leads to a 22% decrease in quantity.
2….使需求量减少22％。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Elastic Demand—— Elasticity is greater than 1
富有弹性的需求——弹性大于1
Quantity 数量
Price
价格
4
$51. A 22%
increase
in price...
1.价格上升
22％… Demand
需求
10050
2. ...leads to a 67% decrease in quantity.
2….使需求量减少67％。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Perfectly Elastic Demand
- Elasticity equals infinity
Quantity
Price
Demand$4
1. At any price
above $4, quantity
demanded is zero.
2. At exactly $4,
consumers will
buy any quantity.
3. At a price below $4,
quantity demanded is infinite.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
完全富有弹性——弹性等于无穷大
数量
价格
需求$4
1. 在任何高于4美元价格时，
2. 需求量为0
2. 在价格正好为4美元时，消费者
将购买任何一种数量。
3. 价格低于4美元时，需求量
是无限的。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Total Revenue and the Price Elasticity of Demand
总收益与需求价格弹性
u Total revenue is the amount paid by buyers
and received by sellers of a good.
总收益是一种物品买者的支付量和卖者得到的量。
u Computed as the price of the good times the
quantity sold.
用该物品的价格乘以销售量来计算。
TR = P x Q
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
$4
Demand
需求
Quantity
数量
P
0
Price
价格
P x Q = $400
(total revenue 总收益)
100
Q
Total Revenue and the Price Elasticity of Demand
总收益与需求价格弹性
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Elasticity and Total Revenue along
a Linear Demand Curve
沿着线性需求曲线的弹性与总收益
With an inelastic demand curve, an increase
in price leads to a decrease in quantity that
is proportionately smaller. Thus, total
revenue increases.
如果需求是缺乏弹性的，价格上升导致需求
量减少的比例小于价格上升的比例，所以总
收益是增加的。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Figure 3 How Total Revenue Changes
When Price Changes: Inelastic Demand
$3
Quantity0
Price
80
Revenue = $240
Demand$1 Demand
Quantity0
Revenue = $100
100
Price
An increase in price
from $1 to $3...
…leads to an increase
in total revenue
from$100 to $240
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
图3.总收益如何随着价格变化而变化：
缺乏弹性的需求
$3
数量0
价格
80
收益=240美元
需求$1 需求
数量0
收益 = 100美元
100
价格
价格从1美元上升到3
美元...
…导致总收益从100美
元增加到240美元
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Elasticity and Total Revenue along
a Linear Demand Curve
沿着线性需求曲线的弹性与总收益
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.
如果需求富有弹性，价格上升导致的需求
量减少的比例大于价格上升的比例，因此
总收益是减少的。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Figure 4 How Total Revenue Changes
When Price Changes: Elastic Demand
Demand
Quantity0
Price
$4
50
Demand
Quantity0
Price
Revenue = $100
$5
20
Revenue = $200
An increase in price
from $4 to $5...
…leads to a decrease
in total revenue
from$200 to $100
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
图4.总收益如何随着价格变化而变化：
富有弹性的需求
需求
数量0
价格
$4
50
数量
数量0
价格
收益 = 100美元
$5
20
收益 =200美元
价格从4美元上升到5
美元…
…导致总收益从200美
元减少到100美元
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
the Elasticity of a Linear Demand Curve
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
线性需求曲线的弹性
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Income Elasticity of Demand
u Income elasticity of demand measures
how much the quantity demanded of a
good responds to a change in consumers’
income.
u It is computed as the percentage change
in the quantity demanded divided by the
percentage change in income.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
需求的收入弹性
u 需求的收入弹性 衡量消费者收入变动
时需求量如何变动。
u 它是需求量变动的百分比除以收入变
动的百分比。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Computing Income Elasticity
计算收入弹性
Income Elasticity
of Demand
需求的收入弹性
Percentage Change
in Quantity Demanded
Percentage Change
in Income
收入变动百分比
=
需求量变动百分比
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Income Elasticity- Types of Goods
收入弹性：不同类型的物品
u Normal Goods 正常物品
u Inferior Goods 劣等品
u Higher income raises the quantity demanded
for normal goodsbut lowers the quantity
demanded for inferior goods.
正常物品：收入提高增加需求量；劣等品：收
入增加减少需求量。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Income Elasticity - Types of Goods -
1. Goods consumers regard as necessities
tend to be income inelastic
Examples include food, fuel, clothing, utilities,
and medical services.
2. Goods consumers regard as luxuries
tend to be income elastic.
Examples include sports cars, furs, and
expensive foods.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
收入弹性：不同类型的物品
u 消费者消费的必需品往往收入弹性小
例如：食物、燃油、衣服、医疗服务。
u 消费者消费的奢侈品往往收入弹性大
例如：运动跑车、皮衣和昂贵物品。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
需求的交叉价格弹性
需求的交叉
价格弹性
物品1需求量变动百分比
物品2价格变动百分比
=
替代品： E>0
互补品： E<0
无关物品：E＝0
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Price Elasticity of Supply
u Price elasticity of supply is the
percentage change in quantity supplied
resulting from a percent change in
price.
u It is a measure of how much the
quantity supplied of a good responds to
a change in the price of that good.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
供给的价格弹性
u 供给价格弹性——价格变动1％引起的
供給量的变动百分比值。
u 它是一种物品的供給量对其价格变动
的反应程度的衡量。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Perfectly Inelastic Supply—— Elasticity equals 0
完全无弹性的供给：弹性等于0
Quantity 数量
Price
价格
4
$5
Supply 供给
100
2. ...leaves the quantity supplied unchanged.
2. …供給量不变。
1. An
increase
in price...
1.价格上
升…
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Inelastic Supply —Elasticity is less than 1
缺乏弹性的供给：弹性小于1
Quantity 数量
Price
价格
4
$51. A 22%
increase
in price...
1.价格上
升22％…
110100
Supply 供给
2. ...leads to a 10% increase in quantity.
2. …引起供給量增加10％。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Unit Elastic Supply——Elasticity equals 1
单位弹性供给：弹性等于1
Quantity 数量
Price
价格
4
$51. A 22%
increase
in price...
1.价格上
升22％…
125100
Supply 供给
2. ...leads to a 22% increase in quantity.
2. …引起供給量增加22％。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Elastic Supply— Elasticity is greater than 1
富有弹性的供给：弹性大于1
Quantity 数量
Price
价格
4
$51. A 22%
increase
in price...
1.价格上
升22％…
200100
Supply 供给
2. ...leads to a 67% increase in quantity.
2. …引起供給量增加67％。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Perfectly Elastic Supply— Elasticity equals infinity
完全有弹性的供给：弹性等于无穷大
Quantity 数量
Price
价格
Supply 供给$4
1. At any price above $4, quantity
supplied is infinite.
1.在任何高于4美元的价格时，
供給量无限。
2. At exactly $4, producers will
supply any quantity.
2.在正好为4美元时，生产者
供给任何一种数量。
3. At a price below $4, quantity supplied is zero.
3.在价格低于4美元时，供給量为0。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Determinants of
Elasticity of Supply
u Ability of sellers to change the amount
of the good they produce.
u Beach-front land is inelastic.
u Books, cars, or manufactured goods are
elastic.
u Time period.
u Supply is more elastic in the long run.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
供给弹性的决定因素
u 卖者改变它们生产物品产量的能力
u 海滩前的土地供给是缺乏弹性的。
u 书、汽车或生产的物品供给是富有弹性的。
u 时间长短
u 供给在长期内更富有弹性。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Computing the Price Elasticity of Supply
The price elasticity of supply is
computed as the percentage change
in the quantity supplied divided by
the percentage change in price.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
计算供给价格弹性
供给价格弹性等于供給量变动百分
比除以价格变动百分比。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
THREE APPLICATIONS OF SUPPLY,
DEMAND, AND ELASTICITY
供给、需求与弹性的三个应用
uCan good news for farming be bad news for
farmers?
农业的好消息会是农民的坏消息吗？
uWhat happens to wheat farmers and the
market for wheat when university agronomists
discover a new wheat hybrid that is more
productive than existing varieties?
当大学的农业科学家培育出能比现有品种更高
产的小麦新杂交品种时，种小麦的农民会怎么
办？小麦市场又会发生什么变动呢？
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
THREE APPLICATIONS OF SUPPLY,
DEMAND, AND ELASTICITY
供给、需求与弹性的三个应用
u Examine whether the supply or demand curve
shifts.
考察是供给曲线还是需求曲线移动。
u Determine the direction of the shift of the
curve.
考虑曲线向哪个方向移动。
u Use the supply-and-demand diagram to see
how the market equilibrium changes.
用供求图说明市场均衡如何变动。
3. ...and a proportionately smaller
increase in quantity sold. As a result,
revenue falls from $300 to $220.
An Increase in Supply in the Market for Wheat
$3
Quantity of Wheat1000
Price of
Wheat 1. When demand is inelastic,
an increase in supply...
Demand
S1 S2
2
110
2. ...leads
to a large
fall in
price...
3. …以及销售量的小幅度增加。结果
收益从300美元减少为220美元。
小麦市场上供给增加
$3
小麦数量1000
小麦价格 1. 当需求缺乏弹性时，
2. 供给增加...
需求
S1 S2
2
110
2. …引起价
格的大幅度
下降...
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Compute the Price Elasticity of Supply
计算供给价格弹性
Demand is inelastic 需求缺乏弹性
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
5
6
$7
4
1
2
3
Quantity 数量
122 4 6 8 10 140
Price
价格 Elasticity is
larger than 1.
弹性大于1
Elasticity is
Smaller than 1.
弹性小于1
Figure 5-5
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
$15
12
3
Quantity
数量
100 200 5000
Price 价格
525
Elasticity is small
(less than 1).
Elasticity is large
(greater than 1).
4
Figure 5-7
弹性小（<1）
弹性大（>1）
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
P2
P1
Quantity of Oil0
Price
of Oil
Demand
S 2 S 1
(a) The Oil Market in the Short Run
P2
P1
Quantity of Oil0
Price
of Oil
Demand
S 2S 1
(b) The Oil Market in the Long Run
2. ...leads
to a large
increase
in price.
1. In the long run,
when supply and
demand are elastic,
a shift in supply...
2. ...leads
to a small
increase
in price.
1. In the short run, when supply
and demand are inelastic,
a shift in supply...
Figure 5-9
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
P2
P1
石油数量
0
石油价格
需求
S 2 S 1
(a) 短期石油市场
P2
P1
石油数量
0
石油价格
需求
S 2S 1
(b) 长期石油市场
2. ..引起
价格大
幅度上升
1. 在长期中，当供给
2. 与需求富有弹性时，供
3. 给移动…
2. ..引起
价格小
幅度上升
1. 在短期中，当供给和需求缺乏
2. 弹性时，供给移动…
Figure 5-9
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
P
2
P1
Quantity of Drugs0 Q2 Q1
Price of
Drugs
Demand
S2
S1
Q2 Q1
(a) Drug Interdiction
Quantity of Drugs0
Price of
Drugs
Supply
D 2
D 1
(b) Drug Education
3. ...and reduces the
quantity sold.
2. ...which
raises the
price...
2. ...which
reduces
the price...
P1
P2
1. Drug interdiction reduces
the supply of drugs...
1. Drug education reduces
the demand for drugs...
3. ...and reduces the
quantity sold.
Figure 5-10
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
P
2
P1
毒品数量0 Q2 Q1
毒品价格
需求
S2
S1
Q2 Q1
(a) 禁毒
毒品数量0
毒品价格
供给
D 2
D 1
(b) 禁毒教育
3. …以及减少
了销售量。
2. …提高
了价格…
2. …降低
了价格…
P1
P2
1. 禁毒减少了毒品供给… 1. 禁毒教育减少了毒品需求…
3. …以及减少
了销售量 。
Figure 5-10
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Summary
u Price elasticity of demand measures how
much the quantity demanded responds to
changes in the price.
u Price elasticity of demand is calculated as the
percentage change in quantity demanded
divided by the percentage change in price.
u If a demand curve is elastic, total revenue
falls when the price rises.
u If it is inelastic, total revenue rises as the
price rises.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
小结
u 需求价格弹性衡量需求量对价格变动
的反应程度。
u 需求价格弹性等于需求量的变化百分
比除以价格的变化百分比。
u 如果需求曲线是富有弹性的，总收益
随着价格的上升而减少。
u 如果 需求曲线是缺乏弹性的，总收益
随着价格的上升而增加。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Summary
n The income elasticity of demand
measures how much the quantity
demanded responds to changes in
consumers’ income.
n The cross-price elasticity of demand
measures how much the quantity
demanded of one good responds to
the price of another good.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
小结
n 需求的收入弹性衡量需求量对消费
者收入变动的反应程度。
n 需求的交叉弹性衡量一种物品的需
求量 对另一种物品价格变动的反应
程度。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Summary
u The price elasticity of supply
measures how much the quantity
supplied responds to changes in the
price.
u In most markets, supply is more
elastic in the long run than in the
short run.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
小结
u 供给价格弹性衡量供給量对价格
变动的反应程度。
u 在大多数市场上，供给在长期中
比在短期中更富有弹性。
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Summary
n The price elasticity of supply is
calculated as the percentage change in
quantity supplied divided by the
percentage change in price.
n The tools of supply and demand can
be applied in many different types of
markets.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
小结
n 供给的价格弹性等于供給量的变化
百分比除以价格的变化百分比。
n 供给和需求作为工具可以用来分析
很多不同的市场。
