Monopoly 獨占、壟斷
獨占的來源
AR(P) 與MR的分離
獨占廠商的最適產量
差別取價
獨占的福利損失

Most of us use Microsoft Windows to run
our computers. Microsoft isn’t a price taker
like the firms in perfect competition.

How does a firm like Microsoft decide the
quantity to produce and the price to charge?
Market Power



Market power and competition are the two forces
that operate in most markets.
Market power is the ability to influence the market,
and in particular the market price, by influencing
the total quantity offered for sale.
A monopoly is an industry that produces a good
or service for which no close substitute exists and
in which there is one supplier that is protected
from competition by a barrier preventing the entry
of new firms.
純粹、完全獨占：
一產業只有一個供給者且沒有相近的替
代品存在，且其他廠商，很難進入市場
No close substitutes
 Barriers to entry

獨占的來源
進入的障礙（barriers to entry）或成本的優勢
１法律限制（郵局）
２專利（製藥 prozac）
３掌控稀少的資源或生產要素
4 高昂的沈沒成本sunk cost（航空）
5 技術上的優越性（microsoft）
6 規模經濟
7 市場需求衰退
自然壟斷
一產業有規模經濟，使單一廠商能以相
當低的平均成本生產物（幾乎）足供整
市場消費的產量
（相較於生產較少數量的小廠商，他們
的AC會較高）
natural monopoly
an industry in which
one firm can supply
the entire market at a
lower price than two
or more firms can.
The ATC curve is
still sloping
downward when it
meets the demand
curve.
Market Power
One firm can
produce 4 units of
output at 5 cents
per unit.
 Two firms can
produce 4 units—2
units each—at 10
cents per unit.

A Single-Price Monopoly’s
Output and Price Decision
Price and Marginal Revenue
A monopoly is a price setter, not a price
taker like a firm in perfect competition.
 The reason is that the demand curve for
the monopoly’s output is the market
demand curve.
 To sell a larger output, a monopoly must
set a lower price.

MR < P, P=AR
Total revenue, TR, is the price, P,
multiplied by the quantity sold, Q.
 Marginal revenue, MR, is the change in
total revenue that results from a one-unit
increase in the quantity sold.
 For a single-price monopoly, marginal
revenue is less than the price at each level
of output. That is,

 MR
<P
單一訂價的廠商，價格滑落時，不但邊
際出售的單價下降，連原先能出售的產
品價格也下降，所以邊際收益低於價格
MR < P
marginal revenue
比較p=16，q=2
以及p=14，q=3
It loses $4 of total
revenue on the 2
units it was selling
at $16 each. And it
gains $14 of total
revenue on the 3rd
unit.So total
revenue increases
by $10
The marginal revenue
curve, MR, passes
through the red dot
midway between 2
and 3 units and at
$10.
MR < P at each
quantity.
 3rd haircut
 P=14
 MR=14*3-16*2

=14-2*2=10

MR
Marginal Revenue
and Elasticity 1
If demand is elastic, a
fall in price brings an
increase in total revenue.
The
rise in revenue from the
increase in quantity sold
outweighs the fall in revenue
from the lower price per unit,
and MR is positive.
Marginal Revenue
and Elasticity 2
If demand is inelastic, a
fall in price brings a
decrease in total revenue.
 The rise in revenue from
the increase in quantity
sold is outweighed by the
fall in revenue from the
lower price per unit, and
MR is negative.

Marginal Revenue
and Elasticity 3


If demand is unit elastic, a
fall in price does not change
total revenue.
The rise in revenue from the
increase in quantity sold
equals the fall in revenue
from the lower price per unit,
and MR = 0.


Total revenue is maximized
when marginal revenue is
zero.
A single-price monopoly
never produces an output
at which demand is
inelastic, i.e. MR<0 .
價格會影響需求量，因此無法以高價出售
很多數量，故需考慮選擇利潤極大化的數
量
MR=MC
MR= △TR／△Q
AR=TR／Q
ＱD=20-Ｐ, P=20-ＱD
TR=P*Q=(20-Q)*Q
MR= △TR／△Q=20-2Q
A Single-Price Monopoly’s
optimal Output
The monopoly faces the same types of
technology constraints as the
competitive firm, but the monopoly
faces a different market constraint.

The monopoly selects the profitmaximizing level of output in the same
manner as a competitive firm, where MR =
MC.
A Single-Price Monopoly’s
Price Decision

The monopoly sets its price at the highest
level at which it can sell the profitmaximizing quantity.

The monopoly may earn an economic
profit, even in the long run, because the
barriers to entry protect the firm from
market entry by competitor firms.
profit-maximizing choices of a
single-price monopolist.

the monopoly sets
the quantity
produced at the
level that maximizes
total revenue minus
total cost.
A SinglePrice
Monopoly’s
profit
Q*=3
 P*=14, ATC=10
 Economic profit
=($14-10)*3
=$12

Equilibrium if the firm is in
perfect competition

where the quantity
demanded equals
the quantity
supplied at
quantity QC and
price PC.
Single-Price Monopoly and
Competition Compared

Equilibrium price
for a monopoly,
PM, occurs on the
demand curve at
the profitmaximizing
quantity.
Efficiency Comparison
competitive
equilibrium is
efficient: MB =
MC.
competitive equilibrium

The sum of the
two surpluses is
maximized and
the efficient
quantity is
produced.
Monopoly is inefficient

because price
exceeds marginal
cost so marginal
benefit exceeds
marginal cost.
Monopoly is inefficient
On all output levels
for which marginal
benefit exceeds
marginal cost, a
deadweight loss is
incurred.
 無謂的損失

Redistribution of Surpluses
Monopoly
redistributes a
portion of
consumer
surplus by
changing it to
producer surplus.
Rent Seeking 1

The social cost of monopoly may exceed
the deadweight loss through an activity
called rent seeking, which is any attempt
to capture consumer surplus, producer
surplus, or economic profit..
Rent Seeking 2

Rent seeking is not confined to a monopoly.
There are two forms of rent seeking activity
to pursue monopoly:
 Buy a monopoly—transfers rent to creator
of monopoly.
 Create a monopoly—uses resources in
political activity.

人為的壟斷
以法律的規定，如証照制，或專利的給
予，所造成的獨占
Rent-Seeking Equilibrium
The resources used
in rent seeking can
exhaust the
monopoly’s
economic profit and
leave the monopoly
owner with only
normal profit.
deadweight loss from
rent seeking

Average total cost
increases and the
profits disappear
to become part of
the enlarged
deadweight loss
from rent seeking.
Price Discrimination
差別取價

Price discrimination is the practice of selling
different units of a good or service for different
prices.

差別取價(price discrimination)是指獨占廠商為
了獲取最大利潤，在生產成本不變情形下，將
同一產品依消費者、市場、地區或購買量的不
同，索取不同價格的現象。例如：公共汽車及
遊樂區等，常將售票分為全票、學生票及半票；
台電公司將用戶分為家庭、商業、工業等用電，
並依不同的用電戶收取不同費率。
Conditions for price
discrimination

Identify and separate different buyer types

市場區隔、不同的需求彈性

Sell a product that cannot be resold

市場封閉

Price differences that arise from cost
differences are not price discrimination.
DVD影片分區
全球軟體及硬體大致區分為八大區
區域不同之軟體無法播放，需將機器改為全區才能讀取
區 別
R1
R2
R3
R4
R5
R6
R7
R8
國
家
美國‧加拿大
歐洲‧日本‧南非‧中東
韓國‧台灣‧香港‧新加坡‧馬來西亞‧印尼
澳洲‧紐西蘭‧中南美洲
印度‧非洲
中國大陸
保留
特別國際管轄地區(含飛機或遊艇)
Price Discrimination and
Consumer Surplus
Price discrimination converts consumer
surplus into economic profit.



A monopoly can discriminate
Among units of a good. Quantity discounts are an
example. (But quantity discounts that reflect lower
costs at higher volumes are not price
discrimination.)
Among groups of buyers. (Advance purchase and
other restrictions on airline tickets are an example.)
Profiting by Price Discriminating
price
discrimination
converts consumer
surplus into
economic profit.
Price Discrimination

As a single-price
monopolist, this
firm maximized
profit by producing
8 units, where MR
= MC and selling
them for $1,200
each.
Price Discrimination
By price
discriminating, the
firm can increase
its profit.
 In doing so, it
converts consumer
surplus into
economic profit.

Perfect Price Discrimination
Perfect price
discrimination
第一級差別取價
extracts the entire
potential consumer
surplus and converts
it to economic profit.
Perfect Price Discrimination

Output increases
to the quantity at
which price equals
marginal cost.
Economic profit
increases above
that earned by a
single-price
monopoly.
 Deadweight loss is
eliminated.

8-3
差別取價的方法

第一級差別取價 (又稱完全差別取價)
指獨占廠商依
據消費者對每
一單位產品所
願支付的最高
價格來收費。
B
D
8-3

第二級差別取價 (又稱階段訂價法)
指獨占廠商對某一特
定數量範圍內的產品
索取某一價格，超出
此一數量後，每增加
某一特定數量的產品，
即索取較低的價格，
故乃對不同級距範圍
內之商品訂立不同價
格，剝奪了部分消費
者剩餘。
a
b
D
8-3

第三級差別取價 (又稱階段訂價法)
指獨占廠商就同一產品，對不同的市場索取
不同的價格；對需求彈性較高的消費者收取
較低的價格，而需求彈性較小的則收取較高
的價格。如學生票、成人票。
第三級差別取價時，如何才能
極大化利潤？
MRa = MRb
彈性小則價格高
Efficiency and Rent Seeking
with Price Discrimination




The more perfectly a monopoly can price
discriminate, the closer its output gets to the
competitive output (P = MC) and the more efficient
is the outcome.
But this outcome differs from the outcome of
perfect competition in two ways:
The monopoly captures the entire consumer
surplus.
The increase in economic profit attracts even
more rent-seeking activity that leads to an
inefficient use of resources.
Monopoly Policy Issues
A single-price monopoly creates
inefficiency and price discriminating
monopoly captures consumer surplus and
converts it into producer surplus and
economic profit.
 And monopoly encourages rent-seeking,
which wastes resources.
 But monopoly brings benefits.

Gains from Monopoly
Product innovation

Patents and copyrights provide protection from
competition and let the monopoly enjoy the profits
stemming from innovation for a longer period of
time.
Economies of scale and scope

Where economies of scale or scope exist, a
monopoly can produce at a lower average total
cost than a large number of competitive firms
could achieve.
Regulating Natural Monopoly

Under natural
monopoly,
government
agencies regulate
the monopoly.
Price regulations under
monopoly


With no regulation,
the monopoly
maximizes profit.
It produces the
quantity at which
marginal revenue
equals marginal
cost.
marginal cost pricing 1


Regulating a natural
monopoly in the public
interest sets output
where MB = MC and
the price equal to
marginal cost.
This regulation is the
marginal cost pricing
rule, and it results in an
efficient use of
resources.
marginal cost pricing 2


With price equal to
marginal cost, ATC
exceeds price and the
monopoly incurs an
economic loss.
If the monopoly
receives a subsidy to
cover its loss, taxes
must be imposed on
other economic activity,
which create
deadweight loss.
average cost pricing


a regulated natural
monopoly might be
permitted to price
discriminate to cover the
loss from marginal cost
pricing.
Another alternative is to
produce the quantity at
which price equals
average total cost and to
set the price equal to
average total cost—the
average cost pricing
rule.
是否獨占廠商一定會賺錢？
視需求而定，如需求很低，仍有可能賠錢
例：微軟第一個operating system要花數百萬
美元製造，但接下來的copy只要很少的錢



diminishing cost
network effect 用的人愈多，則有愈多相關產品
lock in effect 習慣
獨占者的決策
找到使MR=MC之產量Q*
找到Q*對應在需求線上的價格
比較P & AC，賺錢？
一個獨占價格、產量的決定
Q
1
2
3
4
5
6
P
140
107
92
80
66
50
TR
140
214
276
320
330
300
MR
140
74
62
44
10
30
TC
70
120
166
210
253
298
MC TR-TC
70
70
50
164
46
230
44
110
43
77
45
2
P.C. ｖｓ Monopoly
monopoly可持續賺取超額利潤
monopoly生產較少而要價較高 P = MC
生產效率：LR會到LAC的最低?
資源配置的效率
獨占廠商可能試圖改變需求
獨占廠商可能改變成本線
獨占可能促進創新
自然獨占時，單一廠商成本較低
8-4
獨占與完全競爭市場的比較
S1=LMC
L
A
C
E
C
B
F
A
D1=AR1=MR1
G
D2=AR2
MR2
獨占市場的價格歧視
price discrimination
任一產品，廠商出售時，對不同購買者
收取不同價格
提供一產品，縱然供給成本不同，售價
卻相同
100個有錢人，價格忍受上限：$75
1000個窮人，價格忍受上限：$25
如不能歧視：$25 * (100 + 100) = 27500
$75 * 100
=7500
歧視：$25 * 1000 + 75 * 100 = 32500
價格歧視時，利潤通常較高
是否價格歧視都不好？
醫師對窮苦者收較低診療費
允許廠商收取足以支付成本的價格
有些人可能買到較便宜的產品
獨占廠商沒有供給線
由於完全獨占廠商的 AR 為一條負斜率的需求線，且
MR位於AR線的下方，若市場的需求狀況改變，AR與MR
亦會跟著同時變動。
正因為需求面的變化有無限多種，因此有可能在同一
種價格下，獨占廠商會提供不同的產量；或者在相同
的最適產量之下，會出現不同的價格，故在獨占市場
中，無法畫出一條均衡價格與均衡產量間的固定關係，
所以獨占廠商沒有固定的供給線。
8-1
短期虧損，一定得歇業嗎？
1.AR>AVC：廠商宜繼續生產
(1) 廠商繼續生產則會有
藍色面積的虧損
CP*BA發生。
(2) 停業負擔的總固定成
本為面積CHKB。
(3) 繼續生產的虧損（藍
色面積）＜停業負擔
的總固定成本，所以
理性的廠商仍會選擇
繼續生產。
營業虧損
MC
A
C
AVC
B
A
K
E
D=AR
MR
8-1
2.AR=AVC：廠商自由決定經營或停業
(1) 廠商繼續生產仍然有藍色面
積的虧損CP*BA產生。
(2) 假若選擇停止生產，則每單
位產量會有BA的固定成本，
因此停業負擔的總固定成本
為面積CP*AB。
(3) 因此繼續生產的虧損(藍色面
積)＝停業負擔的總固定成
本，在此情況下，廠商的總
收入只夠回收全部的變動成
本，繼續經營與歇業沒有兩
樣。
營業虧損 M C A
C
A
V
C
B
A
E
D=AR
MR
8-1
3.AR=AVC：廠商應關門大吉
(1) 廠商繼續生產一定有藍色面
積的虧損CP*AB產生。
(2) 假若選擇停止生產，則每單
位產量會有BK的固定成本，
因此停業負擔的總固定成本
為面積CHKB。
(3) 由於繼續生產的虧損（藍色
面積）＞停業負擔的總固定
成本(CHKB)，若繼續經營
會連變動成本都無法全部收
回，所以理性的廠商應立刻
結束營業，以減少損失。
營業虧損
MC
A
C
B
A
V
C
K
A
E
D=AR
MR