Transcript Ch4 - Demand

Chapter Four
Demand
© 2008 Pearson Addison Wesley. All rights reserved
2009年 諾貝爾經濟學獎
• 因為經濟治理（economic
governance）方面的卓越
研究成就，雀屏中選。
• 得獎的歐斯特魯姆，成為歷
來第一位諾貝爾經濟學獎女
• 歐斯特魯姆
性得主。
•
•
•
• 評審團說：「歐斯特魯姆與
威廉森的研究顯示，經濟分
析可以闡明大多數社會組織
•
的形式。」
• 資料來源：中央社台北12日 •
綜合外電報導
© 2008 Pearson Addison Wesley. All rights reserved.
•
•
Elinor Ostrom
現年76歲
美國印第安納大 •
•
學任教
自己定位:政治經
濟學家
制度分析理論、 •
集體行動理論、
可持續發展、公
共資源等領域
威廉森
Oliver E.
Williamson
現年77歲
加州大學柏克萊
分校哈斯商學院
任教
被譽為重新發現
「科斯定理」的
人
4-2
前言
• 在經濟蕭條時期，人們的收入和對未來的預期都會降低，人們首先削
減的是大筆消費，如買房、買車、出國旅游等，人們的消費就會轉向
購買廉價商品，如口紅，雖不是生活必需品，卻兼具廉價和粉飾的作
用，能給消費者帶來心理慰藉。
• 口紅效應(Lipstick effect)指一種有趣的經濟現象， 在20世紀30年代美
國經濟大蕭條時期首次提出“口紅效應”。經濟危機也使得如口紅這
類的廉價化妝品大賣。
• 資料來源﹕
http://18dao.jamesqi.com/%E5%8F%A3%E7%BA%A2%E6%95%88%E5%BA%94
© 2008 Pearson Addison Wesley. All rights reserved.
4-3
小包裝立大功 迷你商品勢不可擋
• 【記者孫敏嘉／中正大學報導】
• 你是否曾注意到許多的美妝商品除了正常的規格外，還出現了
迷你型的包裝？
• 中正大學企管系教授曾光華表示，經濟不景氣下，荷包緊縮會
讓消費者更害怕做出錯誤的決定。為了降低購買後才發現不適
用的風險，迷你商品的低價格便成為消費者願意嘗試新產品的
契機，購買過迷你商品的林岱樺就說：「因為價格較便宜，下
手前不會猶豫太久。」
© 2008 Pearson Addison Wesley. All rights reserved.
4-4
小包裝立大功 迷你商品勢不可擋
• 迷你商品特色﹕
– 包裝精緻，外表就像正常規格的縮小版一樣
– 小巧的瓶身方便隨身攜帶，也很適合旅行期間使用
– 讓消費者感覺迷你產品比正品的價格較便宜
• 迷你商品的目的﹕
– 增加試用機會，成功地引發消費者的購買意願，甚至有品牌
因此拉抬了正品的業績
• 資料來源﹕
http://www.peopo.org/portal.php?op=viewPost&articleId=43846
© 2008 Pearson Addison Wesley. All rights reserved.
4-5
Demand
• In this chapter, we examine five main topics.
– Deriving Demand Curves
– Effects of an Increase in Income
– Effects of a Price Increase
– Cost-of-living adjustments
– Revealed Preference
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4-6
Deriving Demand Curves
• System of Demand Equation
We used calculus to maximize utility subject to
a budget constraint. In doing so, we solved for
the optimal quantities that a consumer chooses as
functions of prices and income. That is, we solved
for the consumer’s system of demand functions
for these goods. q  Z  p , p , Y 
1
1
2
q2  B  p1 , p2 , Y 
where p1 is the price of pizza, p2 is the price of
burritos, and Y is her income.
© 2008 Pearson Addison Wesley. All rights reserved.
4-7
Deriving Demand Curves
• Graphical Interpretation
• An individual chooses an optimal bundle of goods
by picking the point on the highest indifference
curve that touches the budget line.
• When a price changes, the budget constraint the
consumer faces shifts, so the consumer choose a
new optimal bundle.
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4-8
Deriving Demand Curves
• By varying one price and holding other prices
and income constant, we can determine how
the quantity demanded changes as the price
changes, which is the information we need to
draw the demand curve.
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4-9
Deriving Demand Curves
• We derive a demand curve using the information
about tastes from indifference curves.
• These indifference curves are convex to the
origin: Mimi views beer and wine as imperfect
substitutes. We can construct Mimi’s demand
curve for beer by holding her budget, her tastes,
and the price of wine constant at their initial
levels and varying the price of beer.
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4-10
Deriving Demand Curves
• Price-consumption curve, is the line through
the equilibrium bundles, such as e1 , e2 ,
and e3 , that Mimi would consume at each
price of beer, when the price of wine and
Mimi’s budget are held constant.
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4-11
Figure 4.1(a)
Deriving Mimi’s Demand Curve
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4-12
Figure 4.1(b)
Deriving Mimi’s Demand Curve
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4-13
Effects of an Increase in
Income
• How Income Changes Shift Demand
Curves
– We illustrate the relationship between the
quantity demanded and income by
examining how Mimi’s behavior changes
when her income rises, while the prices of
beer and wine remain constant.
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4-14
Figure 4.2(a)
Effect of a Budget Increase
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4-15
Figure 4.2(b)
Effect of a Budget Increase
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4-16
Figure 4.2(c)
Effect of a Budget Increase
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4-17
Effects of an Increase in
Income
• The income-consumption curve through
bundles e1 , e2 , and e3 in panel a shows how
Mimi’s consumption of beer and wine increases
as her income rises. As Mimi’s income goes up,
her consumption of both wine and beer
increases.
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4-18
Effects of an Increase in
Income
• Engel curve
– the relationship between the quantity
demanded of a single good and income,
holding prices constant.
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4-19
Consumer Theory and
Income Elasticities
• Income elasticities tell us how much the
quantity demanded changes as income
increases.
• We can use income elasticities to summarize
the shape of the Engel curve, the shape of the
income-consumption curve, or the movement
of the demand curves when income increases.
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4-20
Income Elasticities
• We defined the income elasticities of
demand in Chapter 3 as
percentage change in quantity demanded Q / Q


percentage change in income
Y / Y
where  is the Greek letter xi
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4-21
Consumer Theory And
Income Elasticities
• normal good
– a commodity of which as much or more is
demanded as income rises
• inferior good
– a commodity of which less is demanded as
income rises
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4-22
Income-Consumption Curves
and Income Elasticities
• The shape of the income-consumption curve
for two goods tells us the sign of the income
elasticities: whether the income elasticities for
those goods are positive or negative.
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4-23
Some Goods Must Be Normal
• It is impossible for all goods to be inferior.
• If both goods were inferior, Peter would buy
less of both goods as his income rises-which
makes no sense.
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4-24
Figure 4.3
Income-Consumption Curves and Income
Elasticities
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4-25
Figure 4.4
A Good That
Is Both
Inferior and
Normal
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4-26
Weighted Income Elasticities
• The weighted sum of a consumer’s income
elasticities equals one.
p1q1  p2 q2  ...  pn qn  Y
dqn
dq1
dq2
p1
 p2
 ...  pn
1
dY
dY
dY
pn qn dqn Y
p1q1 dq1 Y p 2 q2 dq2 Y

 ... 
1
Y dY q1
Y dY q2
Y dY qn
11   2 2  ...   n n  1
© 2008 Pearson Addison Wesley. All rights reserved.
4-27
Effects of a Price Increase
• An increase in a price of a good, holding other
prices and income constant, has two effects on
an individual’s demand.
• One is the substitution effect: If utility is held
constant, as the price of the good increases,
consumers substitute other, now relatively
cheaper goods for that one.
© 2008 Pearson Addison Wesley. All rights reserved.
4-28
Effects of a Price Increase
• The other effect is the income effect: An
increase in price reduces a consumer’s buying
power, effectively reducing the consumer’s
income and causing the consumer to buy less
of at least some goods.
© 2008 Pearson Addison Wesley. All rights reserved.
4-29
Income and Substitution
Effects with a Normal Good
• The substitution effect is the change in the
quantity demanded form a compensated change
in the price of CDs, which occurs when we
increase Jackie’s income by enough to offset the
rise in the price of CDs so that her utility stays
constant.
• Jackie’s income effect : The change in income
which is due to the change in the price of CDs,
which allows Jackie to buy fewer units with her
same budget.
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4-30
Income and Substitution
Effects with a Normal Good
• The total effect from the price change is the
sum of the substitution and income effects,
as the arrows (Fig.4.5) show.
• Jackie’s total effect (in CDs per year) from a
rise in the price of CDs is
Total effect= substitution effect + income effect
6

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3

3
4-31
Income and Substitution
Effects with a Normal Good
• Because indifference curves are convex to
the origin, the substitution effect is
unambiguous: Less of a good is consumed
when its price rises. A consumer always
substitutes a less expensive good for a more
expensive one, holding utility constant.
• The substitution effect causes a movement
along an indifference curve.
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4-32
Income and Substitution
Effects with a Normal Good
• The direction of the income effect depends
on the income elasticity.
• Because a CD is a normal good for Jackie, her
income effect is negative. Thus both Jackie’s
substitution effect and her income effect go in
the same direction, so the total effect of the
price rise must be negative.
© 2008 Pearson Addison Wesley. All rights reserved.
4-33
Figure 4.5
Substitution and Income Effects with
Normal Goods
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4-34
Income and Substitution
Effects with an Inferior Good
• If a good is inferior, the income effect goes in
the opposite direction from the substitution
effect.
• For most inferior goods, the income effect is
smaller than the substitution effect. As a result,
the total effect moves in the same direction as
the substitution effect, but the total effect is
smaller.
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4-35
Income and Substitution
Effects with an Inferior Good
• A good is called a Giffen good if a decrease in
its price causes the quantity demanded to fall.
• The Law of Demand was an empirical regularity,
not a theoretical necessity. Although it’s
theoretically possible for a demand curve to slope
upward, economists have found few, if any, realworld examples of Giffen goods.
© 2008 Pearson Addison Wesley. All rights reserved.
4-36
Compensated Demand Curve
• We could derive a compensated demand
curve, where we determine how the quantity
demanded changes as the price rises, holding
utility constant, so that the change in the
quantity demanded reflects only pure
substitution effects when the price changes.
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4-37
Compensated Demand Curve
• It is called the compensated demand curve
because we would have to compensate an
individual - give the individual extra income - as
the price rises so as to hold the individual’s
utility constant.
q1  H  p1 , p2 ,U 
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4-38
Figure 4.6
Deriving
Jackie’s
Compensated
Demand Curve
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4-39
Slutsky Equation
• The usual price elasticity of demand,  ,
captures the total effect of a price change.
We can break this price elasticity of
demand into two terms involving elasticities
that capture the substitution and income
effects.
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4-40
Slutsky Equation
• We measure the substitution effect using the
*

pure substitution elasticity of demand, ,
which is the percentage that the quantity
demanded falls for a given percentage increase
in price if we compensate the consumer to keep
the consumer’s utility constant.
• The income effect is the income elasticity,  ,
times the share of the budget spent on that
good,  .
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4-41
Slutsky Equation
• This relationship among the price elasticity of
demand,  , the substitution elasticity of
*
demand,  , and the income elasticity of
demand,  , is the Slutsky equation.
Total effect= substitution effect + income effect


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
*

  
4-42
Cost-of-Living Adjustments
• By knowing both the substitution and income
effects, we can answer questions that we
could not answer if we knew only the total
effect of a price change.
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4-43
Inflation Indexes
• The price of most goods rise over time. We
call the increase in the overall price level
inflation.
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4-44
Real Versus Nominal Prices
• The actual price of a good is called the
nominal price.
• The price adjusted for inflation is the real
price.
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4-45
Calculating Inflation Indexes
• The CPI for the first year is the amount of
income it takes to buy the market basket actually
purchased that year:
Y1  p C1  p F1
1
C
1
F
The cost of buying the first year’s bundle in the
second year is
Y2  p C1  p F1
2
C
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2
F
4-46
Calculating Inflation Indexes
• To calculate the rate of inflation, we
determine how much more income it would
take to buy the first year’s bundle in the
second year, which is the ratio of Y2 to Y1 :
Y2 p C1  p F1

Y1 p C1  p F1
2
C
1
C
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2
F
1
F
4-47
Calculating Inflation Indexes
• The CPI is a weighted average of the price
2
1
2
1
p
/
p
p
/
p
increase for each good, C C and F
F ,
where the weights are each good’s budget
share in the base year,  C and  F .
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4-48
CPI adjustment
• CPI adjustment to income does not keep an
individual on his original indifference curve, I1.
• Indeed, this person is better off in the second
year than in the first. The CPI adjustment
overcompensates for the change in inflation
in the sense that his utility increases.
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4-49
Figure 4.7
CPI Adjustment
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4-50
Revealed Preferences
• If we observe a consumer’s choice at many
different prices and income levels, we can derive
the consumer’s indifference curves using the
theory of revealed preferences(Samuelson,1947).
• The basic assumption of the theory of revealed
preference is that a consumer chooses bundles
to maximize utility subject to a budget
constraint: The consumer chooses the best bundle
that the consumer can afford.
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4-51
Substitution Effect
• One of the clearest and most important results
from consumer theory is that the substitution
effect is negative: The Law of Demand holds
for compensated demand curves.
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4-52
Figure 4.8
Revealed Preference
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4-53
Substitution Effect
• If he chooses a
a
P
when the price is M , then
PMa M a  PC Ca  PMa M b  PC Cb , or
(4.12)
b
• If he choose b when the price is PM , then
PMb M b  PC Cb  PMb M a  PC Ca , or
(4.13)
• Adding Equation (4.12) and (4.13) together,
(4.14)
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4-54
Consumer Price Indices (CPI)
年
1月
2月
3月
4月
消費者物價指數銜接表
5月
6月
7月
75.89
76.34
75.96
76.46
76.72
76.90
77.43
80
78.75
79.44
79.54
80.83
81.11
80.89
80.30
81
81.62
81.87
82.13
83.07
82.79
84.39
82.94
82
84.00
85.09
84.85
85.62
86.42
86.20
86.37
83
88.40
88.01
88.13
89.42
89.26
90.23
89.70
84
90.42
91.32
90.78
91.95
91.83
92.38
91.00
85
92.20
93.19
91.78
92.41
92.53
94.07
94.01
86
94.04
93.47
94.04
94.36
94.06
95.42
94.80
87
94.42
95.42
93.60
94.27
94.53
94.62
94.02
88
94.90
96.30
94.65
95.44
96.03
95.91
95.38
89
97.14
95.32
95.06
95.84
95.82
95.77
95.48
90
95.51
96.67
95.07
96.04
95.57
95.86
95.87
91
96.55
95.20
94.90
95.94
95.88
95.33
94.93
92
96.56
95.81
95.75
96.85
96.76
96.99
98.10
93
97.03
97.67
97.95
98.44
98.99
99.30
100.45
94
99.62
98.63
98.35
99.65
100.56
101.02
101.24
95
99.97
100.36
99.19
100.33
100.54
101.15
100.91
96
104.23
103.10
104.22
104.27
106.18
106.77
97 102.91
102.84
102.95
103.74
104.18
104.08
104.29
98 104.43
註：1.由於受查者延誤或更正報價，最近3個月資料均可能修正。
2.表列指數民國59年（含）以前係依據台灣省政府編布之指數銜接。
© 2008 Pearson Addison Wesley. All rights reserved.
8月
9月
10月
基期：民國95年 =100
累計平均
11月
12月
77.61
79.93
82.59
88.42
89.93
94.46
93.92
94.33
95.41
95.68
96.11
95.84
95.28
97.71
101.20
100.63
102.25
107.04
106.17
77.72
82.51
83.12
88.68
90.46
93.94
94.52
94.91
95.47
97.02
96.52
95.78
95.57
98.24
101.34
100.09
103.20
106.40
78.49
82.48
83.49
87.72
90.24
93.56
93.26
95.67
96.06
97.04
97.98
96.31
96.26
98.56
101.26
100.06
105.39
107.91
78.72
81.16
83.67
86.92
90.60
93.50
93.01
96.64
95.78
97.94
96.82
96.28
95.83
97.30
99.73
99.97
104.77
106.80
77.97
80.63
84.36
86.60
90.56
92.85
93.09
95.06
95.20
96.77
95.14
95.86
95.81
97.36
99.51
100.18
103.52
104.83
77.18
80.63
83.00
86.41
89.58
92.33
93.17
94.73
94.90
96.09
96.08
95.89
95.62
97.17
99.41
100.00
101.80
105.39
104.09
4-55
Consumer Price Indices (CPI)
消費者物價指數對上年同月漲跌率(％)
年
1月
2月
3月
4月
5月
6月
7月
8月
9月
80
4.99
5.76
4.46
4.11
3.40
4.03
4.06
2.59
-0.72
81
3.77
4.06
4.71
5.72
5.72
5.19
3.71
2.99
6.16
82
3.64
3.06
3.26
2.77
2.07
4.33
3.29
3.33
0.74
83
2.92
3.93
3.31
3.07
4.38
2.14
4.14
7.06
6.69
84
5.24
3.43
3.87
4.44
3.29
4.68
3.86
1.71
2.01
85
2.29
3.76
3.01
2.83
2.88
2.38
1.45
5.04
3.85
86
1.97
2.05
1.10
0.50
0.76
1.83
3.31
-0.57
0.62
87
2.00
0.30
2.46
2.11
1.65
1.44
0.84
0.44
0.41
88
0.40
2.09
-0.47
-0.10
0.50
-0.84
-0.82
1.14
0.59
89
0.51
0.92
1.12
1.24
1.59
1.36
1.45
0.28
1.62
90
2.36
-1.02
0.43
0.42
-0.22
-0.15
0.10
0.45
-0.52
91
-1.68
1.42
0.01
0.21
-0.26
0.09
0.41
-0.28
-0.77
92
1.09
-1.52
-0.18
-0.10
0.32
-0.55
-0.98
-0.58
-0.22
93
0.01
0.64
0.90
0.95
0.92
1.74
3.34
2.55
2.79
94
0.49
1.94
2.30
1.64
2.30
2.38
2.40
3.57
3.16
95
2.67
0.98
0.41
1.23
1.59
1.73
0.79
-0.56
-1.23
96
0.35
1.75
0.85
0.68
-0.02
0.13
-0.33
1.61
3.11
97
2.94
3.86
3.94
3.88
3.71
4.97
5.81
4.68
3.10
98
1.48
-1.33
-0.15
-0.46
-0.09
-1.98
-2.32
-0.81
註：1.由於受查者延誤或更正報價，最近3個月資料均可能修正。
2.各月年增率係以其對應指數(取2位小數)計算而得；年指數係1-12月之算數平均，其年增率以
平均後之原始值計算，相關表件受限於版面，僅顯示2位小數，累計平均指數算法亦同。
© 2008 Pearson Addison Wesley. All rights reserved.
10月
2.49
5.08
1.22
5.07
2.87
3.68
-0.32
2.58
0.41
1.02
0.97
-1.70
-0.05
2.39
2.74
-1.19
5.33
2.39
11月
4.81
3.10
3.09
3.88
4.23
3.20
-0.52
3.90
-0.89
2.26
-1.14
-0.56
-0.47
1.53
2.50
0.24
4.80
1.94
12月
3.88
3.41
4.63
2.66
4.57
2.53
0.26
2.12
0.15
1.65
-1.68
0.76
-0.05
1.62
2.21
0.67
3.33
1.27
累計平均
3.62
4.47
2.94
4.10
3.67
3.07
0.90
1.68
0.18
1.25
-0.01
-0.20
-0.28
1.61
2.31
0.60
1.80
3.53
-0.72
4-56