Transcript 個別的需求與選擇

消費者的選擇：
個人需求和市場需求的導出
什麼是預算限制？
預算線的導出
價格、所得改變對預算線
的影響
什麼是效用？
無異曲線的導出
什麼是消費者的最適選擇？
價格、所得改變如何影響消費者的均衡？
範例:工作與休閒的選擇
個人需求和市場需求的導出
2
預算的限制



預算線：有限所得最多可購買的各種產品的組
合（消費的客觀限制）
graphical representation of all possible
combinations of a household’s purchases of
two goods, given their prices and a fixed
amount of money to spend
the maximum amounts of the goods the
consumer can afford
預算線
Expenditure = Income
支出 = 所得
the price of soda PS,
the quantity of soda
QS, the price of a
movie PM, the quantity
of movies QM, and
income Y.
budget equation is:
PSQS + PMQM = Y.
4
預算線的截點

原所得 =$30，Pmovie=$6, Psoda=$3

可購買最多的電影票
(movie，soda)=(5 ，0)



可購買最多的可樂
(movie，soda)=(0 ，10)
5
Consumption Possibilities
PSQS + PMQM = Y
Divide both sides of this equation by PS, to give:
 QS + (PM/PS)QM = Y/PS





Then subtract (PM/PS)QM from both sides of the
equation to give:
 QS = Y/PS – (PM/PS)QM
The term Y/PS is Lisa’s real income in terms of
soda. 以可樂計算的實質所得
The term PM/PS is the relative price of a movie in
terms of soda. 電影(以可樂價格計算)的相對價格
6
價格改變使預算線
轉動

原所得 =$30，Pmovie=$6, Psoda=$3

P’soda=$1.5
可購買最多的電影票
(movie，soda)=(5 ，0)
可購買最多的可樂
(movie，soda)=(0 ，20)




7
A BUDGET LINE
soda
20
18
16
14
12
10
8
6
4
2
0
1
2
3
4
5
Copyright  2000 by Harcourt, Inc. All rights reserved.
6
7
Consumption Possibilities


A fall in the price of
the good on the x-axis
increases the
affordable quantity of
that good and
decreases the slope
of the budget line.
relative price相對價格
的改變
9
所得改變使預算線
平行移動

原所得 =$30，Pmovie=$6, Psoda=$3

價格不變而所得 增加至$36，預算線向外移出

價格不變而所得 減少至 $?，預算線向內移入
10
soda
A BUDGET LINE
12
10
A
G
B
8
C
6
4
D
2
E
0
1
2
3
4
5
Copyright  2000 by Harcourt, Inc. All rights reserved.
6
7
Consumption Possibilities


An change in the
household’s income
brings a parallel shift of
the budget line.
The slope of the budget
line doesn’t change
because the relative
price doesn’t change..
12
預算線的斜率




ΔS/ΔM= income/Ps = Pm / Ps
income/Pm
在所得不變的情況下，增加一單位M的消費，
所必須放棄的S
(與Pm成正比，與Ps成反比)
13
滿足感 satisfaction

快樂的程度

有朋自遠方來，不亦樂乎?
與其錦上添花，不如雪中送炭

效用 Utility


消費的目的: 自身的滿足、快樂
選擇是為了帶給自己快樂

「沒有人每天釣魚、打高爾夫球。如果每天都做這些
事，其實是很痛苦的。打高爾夫球、釣魚和旅行之所
以快樂，是因為這些事情並非日常之事。」
～～大前研一

為自己而活 /為別人而活
不知為何而戰？

消費者的選擇

有限所得 limited income
如何達到最大的快樂? Maximize utility

快樂的存量stock 和增加量increment

快樂的程度有高低之分


有1朋自遠方來，有2朋自遠方來
有3朋自遠方來
17
快樂的增加速度有高低之分


有1朋自遠方來，有2朋自遠方來
有3朋自遠方來
18
快樂的衡量



效用線, 無異曲線 (indifference curve)：
所有能達到某一特定滿足水準的消費組合（主
觀偏好）
a line connecting all combinations of goods
that are equally desirable
無異曲線


An indifference curve
joins all those points
that Lisa says are just
as good as C
G is such a point.
Lisa is indifferent
between C and G..
20
Preferences and Indifference
Curves

All the points above the
indifference curve are
preferred to the points on
the curve.

And all the points on
the indifference
curve are preferred
to the points below
the curve.
21
Preferences and Indifference
Curves
An indifference curve
above I1 is I2 . All the
points on I2 are
preferred to those on
I1 .
 無異曲線愈高，滿足程
度愈高
 For example, point J
is preferred to either
point C or point G.

22
總效用(Total utility) TU




消費者願意用以交換該物之最高金額
TOTAL UTILITY: the maximum amount of
money that a consumer is willing to pay for
a quantity of a good.
例：為1條牛仔褲願付最高價
TU1=800元
邊際效用(marginal utility) MU



消費者願意用以交換一單位該物之最大金額
the maximum amount of money that a
consumer she or he is willing to pay for one
more unit of a good.
例: 為2條牛仔褲願付最高價=1500元


TU2牛仔褲=1500元
MU牛仔褲1=800元 ， MU牛仔褲2=700元
TOTAL AND MARGINAL UTILITY FOR PIZZA
(1)
(2)
Quantity (Q)
Serving per month
0
1
2
3
4
5
6
7
8
Total Utility
(TU)
$ 0.00
15.00
28.00
40.50
52.00
60.00
65.00
68.00
68.00
.
Copyright  2000 by Harcourt, Inc. All rights reserved.
(3)
Marginal Utility
(MU = TU/Q)
$15.00
13.00
12.50
11.50
8.00
5.00
3.00
0.00
邊際效用遞減法則(The law of
diminishing marginal utility)

當一物的消費增加，它的邊際效用會愈來愈小

“LAW” OF DIMINISHING MARGINAL
UTILITY: additional units of a commodity are
worth less and less to a consumer in money
terms.
Household Consumption
Choices

Marginal Utility



Marginal utility is the change in total utility that
results from a one-unit increase in the quantity of
a good consumed.
As the quantity consumed of a good increases,
the marginal utility from consuming it decreases.
We call this decrease in marginal utility as the
quantity of the good consumed increases the
principle of diminishing marginal utility.
28
Household Consumption
Choices

Figure 7.2(b) illustrates diminishing marginal utility.

Utility is analogous
to temperature.
Both are abstract
concepts and both
are measured in
arbitrary units.

29
水與鑽石的矛盾
paradox of value


水可以救命總效用高
鑽石的價格卻遠高於水:價格依邊際效用而定
31
Indifference curves do not
cross
32
無異曲線可能有不同的形狀






U=x*y, U=4
(x,y)可包括下列組合:
(1,4)(2,2)(4,1)
如U=2x+y , U=4
(x,y)可包括下列組合:
(1,2) (2,0) (1.5,1)
33
無異曲線不同的形狀代表不同的
替代程度

Degree of Substitutability

The shape of the indifference curves reveals the
degree of substitutability between two goods..
完全替代
完全互補
34
無異曲線的斜率






效用 U = x*y
MUx=y
MUy=x
ΔY/ΔX= ΔU/ΔX = MUx / MUy
ΔU/ΔY
保持固定的效用下，增加一單位X的消費，所
必須放棄的Y
35
Figure 2 The Consumer’s
Preferences
Quantity
of Pepsi
C
B
MRS
D
I2
1
A
0
Indifference
curve, I1
Quantity
of Pizza
36
Marginal Rate of Substitution

邊際替代率


The marginal rate of substitution, (MRS),
measures the rate at which a person is willing to
give up good y, (the good measured on the y-axis)
to get an additional unit of good x (the good
measured on the x-axis) and at the same time
remain indifferent (remain on the same
indifference curve).
在效用不變的條件下，消費者願意用多少的y 換取
額外一單位的x
37
Preferences and Indifference
Curves




If the indifference curve is relatively steep, the
MRS is high.(y的邊際效用高)
In this case, the person is willing to give up a
large quantity of y to get a bit more x.
If the indifference curve is relatively flat, the MRS
is low. .(y的邊際效用變低)
In this case, the person is willing to give up a
small quantity of y to get more x.
38
Preferences and Indifference
Curves




A diminishing marginal rate of substitution is the
key assumption of consumer theory.
A diminishing marginal rate of substitution
邊際替代率遞減
is a general tendency for a person to be willing to
give up less of good y to get one more unit of
good x, and at the same time remain indifferent,
as the quantity of good x increases.
39
Figure 4 Bowed Indifference
Curves
Quantity
of Pepsi
14
MRS = 6
A
8
1
4
3
0
B
MRS = 1
1
2
3
6
Indifference
curve
7
Quantity
of Pizza
40
Preferences and Indifference
Curves


At point C, Lisa is
willing to give up 2
six-packs to see
one more movie—
her MRS is 2.
At point G, Lisa is
willing to give up
1/2 a six-pack to
see one more
movie—her MRS is
1/2.
41
Maximizing Utility


The key assumption of marginal utility theory is
that the household chooses the consumption
possibility that maximizes total utility.
The Utility-Maximizing Choice


We can find the utility-maximizing choice by
looking at the total utility that arises from each
affordable combination.
Table 7.2 (page 153) shows an example of the
utility-maximizing combination, which is called a
consumer equilibrium. 消費者的均衡
42
Maximizing Utility

Equalizing Marginal Utility per Dollar Spent



Using marginal analysis, a consumer’s total utility
is maximized by following the rule:
Spend all available income and equalize the
marginal utility per dollar spent on all goods.
The marginal utility per dollar spent is the
marginal utility from a good divided by its price.
43
Maximizing Utility






Call the marginal utility of movies MUM
Call the marginal utility of soda MUS
Call the price of movies PM
Call the price of soda PS
The marginal utility per dollar spent on movies is
MUM/PM
The marginal utility per dollar spent on soda is
MUS/PS.
44
Maximizing Utility




Total utility is maximized when:
 MUM/PM = MUS/PS
Table 7.3 (page 154) and Figure 7.3 on the next slide show
why the utility maximizing rule works.
最後花的一塊錢，得到的邊際效用要相同
錢花在刀口上
45
消費者的最適選擇(均衡)
The Consumer’s Optimum
Quantity
of Pepsi
The consumer would prefer to
be on indifference curve I3, but
does not have enough income
to reach that indifference curve.
Optimum
B
A
I3
I2
I1
The consumer can afford
most of the bundles on I1,
but why stay there when
you can move out to a
higher indifference curve, I2?
Budget constraint
0
Quantity
of Pizza
46
Maximizing Utility

If MUM/PM > MUS/PS, then moving a dollar from
soda to movies increases the total utility from
movies by more than it decreases the total utility
from soda, so total utility increases.

Only when MUM/PM
= MUS/PS, is it not
possible to
reallocate the
budget and increase
total utility.
47
Maximizing Utility

Similarly, if MUS/PS > MUM/PM, then moving a
dollar from movies to soda increases the total
utility from soda by more than it decreases the
total utility from movies, so total utility increases.

Again, only when
MUM/PM = MUS/PS, is
it not possible to
reallocate the
budget and increase
total utility.
49
Predicting Consumer Behavior
 The
consumer’s best affordable point is:
 On the budget line 在預算線上
 On the highest attainable indifference curve 可達到
最大效用(的無異曲線)
 Has a marginal rate of substitution between the two
goods equal to the relative price of the two goods
51
Predicting Consumer Behavior
Lisa
can afford to
consume more soda and
fewer movies at point F.
And she can afford to
consume more movies
and less soda at point H.
But she is indifferent
between F, I, and H and
she clearly prefers C to I.
52
最適消費



Max U=x*y
s.t. 6x+3y=30
MUx = Px
MUy
Py
y/x =6/3
U*=12.5
12x=30
(x*,y*)=(2.5, 5)
53
如果非最適消費

MUx > Px 或 MUx > MUy
MUy
Py
Px
Py
在所得相同的情況下，增加x的消費，減少y的消
費，可以得到更高的效用
MUx/ Px: 每花一元買x可以得到的邊際效用
54



Jane is maximizing total utility while
consuming food and clothing. Her marginal
utility from food and clothing are 50 utils and
25 utils, respectively. If clothing is priced at
$5 per unit, the price of food must
A) be rising. B) be falling. C) equal $10. D)
equal $20.
ANS: C
55
Predicting Consumer Behavior
point F, Lisa’s MRS is
greater than the relative
price.
At point H, Lisa’s MRS is
less than the relative
price..
At point C, Lisa’s MRS is
equal to the relative price.
At
56
價格或所得的改變會影響最適消
費組合

當A變貴，通常應降低A的消費量，增加B的消
費量
預算不變，價格改變
求出一條需求線

The price of a movie then
falls to $3. 價格下跌
The budget line rotates outward.
Lisa’s best affordable point is
now J in part (a).
In part (b), Lisa moves to point
B, which is a movement along
her demand curve for movies.
P=6, Q=6; P=3, Q=5
58
個人需求線的導出
Deriving the Demand Curve
(a) The Consumer’
s Optimum
Quantity
of Pepsi
750
(b) The Demand Curve for Pepsi
Price of
Pepsi
New budget constraint
B
$2
A
I2
B
250
1
A
Demand
I1
0
Initial budget
constraint
Quantity
of Pizza
0
250
750
Quantity
of Pepsi
59

價格不變，預算改變
求出2條需求線上不同的點
A Change in Income



The effect of a change in
income on the quantity of a
good consumed is called the
income effect 所得效果.
Figure 8.8 illustrates the
effect of a decrease in Lisa’s
income.
Initially, Lisa consumes at
point J in part (a) and at point
B on demand curve D0 in part
(b).
60
價格不變，預算改變
求出2條需求線上不同的點

Lisa’s income decreases
and her budget line shifts
leftward in part (a).
Her new best affordable point is
K in part (a).
Her demand for movies
decreases, shown by a leftward
shift of her demand curve for
movies in part (b).
Y= 30 Q=5; Y=21, Q=4
61
價格的改變具2種效果




東西變便宜了
文大頭好像變有錢了
替代效果
所得效果
62
Predicting Consumer Behavior

Initially, Lisa has an
income of $30, the
price of a movie is $6,
and she consumes at
point C. The price of a
movie falls from $6 to
$3 and her budget line
rotates outward. Lisa’s
best affordable point is
then J.
63
Predicting Consumer Behavior


We’re going to break
the move from C to J
into two parts.
The first part is the
substitution effect and
the second is the
income effect.
64
替代效果substitution effect
在維持同樣效用的條件下，
文大頭因為電影變便宜，
因而多看的電影:
(用較便宜的消費取代較貴的
消費)
 The substitution effect is
the first reason why the
demand curve slopes
downward.
65
所得效果 income effect
在維持同樣相對價格的條
件下，文大頭因為實質
所得增加，因而多看的
電影:
The move from K to J is
the income effect.
substitution effect =4 movie
income effect =1 movie
66
價格下降的替代效果

只要價格下降，替代效果一定是增加消費
67
價格下降的所得效果

價格下降，所得效果不一定是增加消費
68
依據所得效果將產品分類


正常財normal good
劣等財inferior good
69
正常財
normal good


所得增加，所得效果是
增加消費
income effect is
positive
70
劣等財
inferior good


所得增加，所得效果是
減少消費
income effect is
negative
71
Predicting Consumer Behavior


If the negative income effect
is stronger than the
substitution effect, a lower
price for inferior goods
brings a decrease in the
quantity demanded—the
demand curve slopes
upward!
This case has not been
found in any real-world
market.
72
Figure 10 Income and
Substitution
Effects
Quantity
of Pepsi
New budget constraint
C New optimum
Income
effect
B
Substitution
effect
Initial
budget
constraint
Initial optimum
A
I2
I1
0
Substitution effect
Income effect
Quantity
of Pizza
73
工作與休閒的選擇






勞動供給:
人如何決定工作時數？
工作可得到「所得」
不工作可得到「休閒」
U= (休閒,所得)
休閒的代價是損失的工資
74
Work-Leisure Choices







完全不工作，一週可
休閒168小時
休閒下限100小時
完全工作，每小時工
資5元
一週可賺$5*68=$340
工資提高，休閒變貴
(機會成本提高)
預算線向上轉出
75
Work-Leisure Choices


工資提高，休閒變貴，
替代效果為負向，休
閒應減少.
工資提高，如休閒是
正常財，所得效果為
正向，休閒應增加.
76
Work-Leisure Choices

The Labor Supply
Curve



工資是休閒的代價
工資提高，休閒變貴，
替代效果為負向，休閒
應減少.
工資提高，如休閒是正
常財，所得效果為正向，
休閒應增加.
77
Work-Leisure Choices




如果所得效果小於替代效
果，則休閒減少
The move from A to B
如果所得效果大於替代效
果，則休閒增加
The move from B to C
78
後彎的勞動供給線


The move from A to B
所得效果小於替代效果
重賞之下有勇夫
The move from B to C所得
效果大於替代效果
錢多事少離家近
79
市場的需求
個人需求的水平加總
80
60
20
5
7
10
甲
乙
19
9
12
市場
80
Predictions of Marginal Utility
Theory

A Fall in the Price of a Movie



When the price of a good falls the quantity
demanded of that good increases—the demand
curve slopes downward.
For example, if the price of a movie falls, we know
that MUM/PM rises, so before the consumer
changes the quantities consumed, MUM/PM >
MUS/PS.
To restore consumer equilibrium (maximum total
utility) the consumer increases the quantity of
movies consumed to drive down the MUM and
restore MUM/PM = MUS/PS.
81
Predictions of Marginal Utility
Theory



A change in the price of one good changes the
demand for another good.
You’ve seen that if the price of a movie falls,
MUM/PM rises, so before the consumer changes
the quantities consumed, MUM/PM > MUS/PS.
To restore consumer equilibrium (maximum total
utility) the consumer decreases the quantity of
soda consumed to drive up the MUS and restore
MUM/PM = MUS/PS.
82
Predictions …

Table 7.4 and Figure 7.4 illustrate these
predictions.

A fall in the price of a
movie increases the
quantity of movies
demanded—a
movement along the
demand
curve for
and decreases
the
movies,
demand for soda—a

shift of the demand
curve for soda.
83
Predictions of Marginal Utility
Theory

A Rise in the Price of Soda



Now suppose the price of soda rises.
We know that MUS/PS falls, so before the
consumer changes the quantities consumed,
MUS/PS < MUM/PM.
To restore consumer equilibrium (maximum total
utility) the consumer decreases the quantity of
soda consumed to drive up the MUS and
increases the quantity of movies consumed to
drive down MUM. These changes restore MUM/PM
= MUS/PS.
85
Predictions …

Table 7.5 and Figure 7.5 illustrate these
predictions.

A rise in the price of
soda decreases the
quantity of soda
demanded—a
movement along the
demand
curve the
for
and increases
soda,
demand for movies—

a shift of the demand
curve for movies.
86
Predictions of Marginal Utility
Theory

A Rise in Income



When income increases, the demand for a normal
good increases.
Table 7.6 illustrate this prediction
Table 7.7 summarizes the assumptions and
predictions of marginal utility theory.
88
Predictions of Marginal Utility
Theory

Individual Demand and Market Demand



The market demand for a good is the relationship
between the price of the good and total quantity
demanded of that good.
The individual demand for a good is the
relationship between the price of the good and the
quantity demanded by one person.
Figure 7.6 on the next slide shows how we sum
the individual demand curves to obtain the market
demand.
89
Predictions of Marginal Utility
Theory
90
Predictions of Marginal Utility
Theory

Marginal Utility and Elasticity


We can predict the price elasticity of demand for a
good by knowing the characteristics of the
marginal utility of the good.
If as the quantity consumed, marginal utility
diminishes rapidly, then a given price change will
bring a small quantity change to restore consumer
equilibrium, and demand will be inelastic.
91
Efficiency, Price, and Value

Consumer Efficiency and Consumer Surplus


When consumers maximize their utility, they are
using resources efficiently.
And the marginal benefit from a good or service is
the maximum price the consumer is willing to pay
for an extra unit of that good or service when his
or her utility is maximized.
92
Efficiency, Price, and Value


The Paradox of Value
鑽石與水的矛盾


The paradox of value “Why is water, which is
essential to life, far cheaper than diamonds, which
are not essential?” is resolved by distinguishing
between total utility and marginal utility.
Figure 7.7 on the next slide illustrates the
resolution of the paradox.
93
Efficiency, Price, and Value

The total utility and consumer surplus from water
is large but the marginal utility and price of water
is small.

In contrast, the total
utility and consumer
surplus from
diamonds is small
but the marginal
utility and price of a
diamond is large.
94