Download 9_ 完全競爭_ch14

完全競爭
Perfect Competition
Opening up the big box
Feb 23rd 2006
From The Economist print edition
Measuring the Wal-Mart effect
The Waltons, the founding family of Wal-Mart,
opened their first store in the state in 1962.
Wal-Mart now has 3,800 shops nationwide.
The discount retailer is the world's biggest
company by sales: a record $312.4 billion in
the last fiscal year, according to figures
released this week.
Measuring the Wal-Mart effect
The Wal-Mart Effect”, Charles Fishman notes
that he could read all of the significant
academic papers on the company's impact on




prices
jobs
suppliers
competitors
in a couple of afternoons at the library.
This was partly due to a “paucity of data”,
writes Emek Basker, an economist at the
University of Missouri, whose requests for
numbers from the company were denied.
America is home to more Wal-Mart
employees (1.3m) than high-school
teachers.
A typical store is manned by 150-350
people;
the bigger “supercentres”, which sell
groceries, employ 400-500.
But even as Wal-Mart creates some
jobs, it displaces others.
What is the net effect?
Global Insight, a research
company
“new businesses spring up near Wal-Marts
and existing stores flourish as they take
advantage of the increased customer flow to
and from our stores.”
Global Insight reckons that a 100,000 squarefoot (9,300 square-metre) Wal-Mart creates
97 retail jobs,
after the dust has settled, but destroys 30 in
wholesale.
This result may, however, be flawed—
for the familiar reason that correlation
does not prove causation. (因果缪誤)
Wal-Mart, after all, does not set up shop
at random.
All else equal, it is presumably attracted to
relatively thriving retail markets, with robust
sales and hence strong employment.
 Its entry into a neighbourhood may be the
result, not the cause, of high retail
employment there.

David Neumark, Junfu Zhang and
Stephen Ciccarella, of the Public Policy
Institute of California, a think-tank
measuring the impact of one thing (exposure
to Wal-Mart) on another (the health of local
retailing).
They use a proxy for the first variable that is
not itself affected by the second.
That proxy is distance, measured in miles
from Bentonville, the company's place of
origin.
Wal-Mart spread like a “wave”, rippling
outwards from its Arkansas epicentre in
a widening circle.
It reached California only in 1990 and
New England a year later. The greater a
county's distance from Bentonville, the
later Wal-Mart's arrival there, regardless
of the county's retailing appeal.
The authors track Wal-Mart's progress
through 3,032 counties from 1977 to 1995.
The arrival of a store in a typical county
destroys about 180-270 retail jobs, they
conclude, which suggests that each Wal-Mart
associate does the job of 1.5-1.75 people at a
rival.
However, this does not imply a rise in overall
joblessness: those displaced by Wal-Mart will
tend to find work elsewhere.
What about wages?
Mr Neumark and his colleagues estimate
Wal-Mart's impact on retail payrolls, which
averaged $13,860 per worker in their sample.
The opening of a Wal-Mart store reduces
these by only about 1%.
Whether this was because hours shorten,
wages fall or low-paid jobs displace well-paid
jobs, they could not tell.
The other side of the coin
Wal-Mart may shave payrolls, but it
slashes shopping bills—even for people
who never shop there.
Ms Basker estimates that the prices of
goods such as toothpaste, shampoo,
aspirin and laundry detergent fall by 713% five years after Wal-Mart's arrival
in a city.
Messrs Hausman and Leibtag reckon
the existence of big-box retailers, such
as Wal-Mart, is a substantial boon to
shoppers—equivalent to offering
households 25 cents back for every
dollar they spend on groceries, or about
$450 a year on average.
Some of Wal-Mart's detractors think it
“cheerless”, others mean.
But what Wal-Mart saves on its payrolls
it passes on to consumers. There are
two sides to every penny it pinches.
什麼樣的競爭環境使廠商很有效率，消
費者不會被剝削？
完全競爭市場的重要特性
這些特性如何影響廠商長、短期產量
這些特性如何影響廠商長、短期價格與
利潤
消費者有很多選擇
產品沒有特色
消息又快又正確
沒有舉足輕重的大廠商
也沒有舉足輕重的大客戶
Competition
 Perfect
competition is an industry in which:
 Many firms sell identical products to many
buyers.
 There are no restrictions to entry into the
industry.
 Established firms have no advantages over
new ones.
 Sellers and buyers are well-informed about
prices.
Competition
How Perfect Competition Arises
 When
a firm’s minimum efficient scale is
small relative to market demand so there is
room for many firms in the industry
 And when each firm is perceived to produce a
good or service that has no unique
characteristics, so consumers don’t care
which firm they buy from
Competition
Price Takers




In perfect competition, each firm is a price taker.
A price taker 價格接受者 is a firm that cannot
influence the price of a good or service.
No single firm can influence the price—it must
“take” the equilibrium market price.
Each firm’s output is a perfect substitute for the
output of the other firms, so the demand for each
firm’s output is perfectly elastic.
Competition
Economic Profit and Revenue
The goal of each firm is to maximize
economic profit, which equals total revenue
minus total cost.
 Total cost is the opportunity cost of
production, which includes normal profit.
 A firm’s total revenue equals price, P,
multiplied by quantity sold, Q, or P  Q.

Competition


A firm’s marginal revenue is the change in total
revenue that results from a one-unit increase in
the quantity sold.
因為個別廠商都很小，不需降價吸引顧客，在市場
價格下即可將所有產品賣出
The Firm’s Decisions in
Perfect Competition
A
perfectly competitive firm faces two
constraints:
 A market constraint summarized by the
market price and the firm’s revenue curves
 A technology constraint summarized by the
firm’s product curves and cost curves (like
those in Chapter 10)
The Firm’s SR Decisions in
Perfect Competition
 短期的決策:產量>0
? 產量應該多少(使自己利
潤最大)?
 Whether to produce or to shut down.
 If the decision is to produce, what quantity to
produce.
A firm’s long-run decisions are:
長期的決策: 適當的規模是什麼？
 要繼續留在這一行嗎？
 Whether to increase or decrease its plant
size.


Whether to stay in the industry or leave it.
The Firm’s Decisions in
Perfect Competition
利潤最大的產量
Profit-Maximizing Output
Π= TR-TC
=p*q – TVC - TFC
毛衣廠商的利潤 p=25
Quantity
TR
TC (假設)
π =TR-TC
0
0
22
-22
4
100
100
0
8
200
160
40
9
225
183
42
11
275
245
30
13
325
360
-35
The Firm’s
Decisions
in Perfect
Competition
Part (a) also shows the
total cost curve, TC,
which is like the one in
Chapter 10.
Total revenue minus total
cost is profit (or loss),
shown in part (b).
The Firm’s
Decisions
in Perfect
Competition

Profit is maximized
when the firm produces
9 sweaters a day.
At low output levels, the
firm incurs an economic
loss—it can’t cover its
fixed costs.

At intermediate output
levels, the firm earns
an economic profit.
At high output levels, the
firm again incurs an
economic loss—now it
faces steeply rising costs
because of diminishing
returns.
The Firm’s optimal output in
Perfect Competition
Marginal Analysis
the profit-maximizing output.
profit is maximized by producing the
output at which marginal revenue, MR,
equals marginal cost, MC.
The Firm’s Decisions in
Perfect Competition
If MR > MC,
economic profit
increases if output
increases.
If MR < MC, economic
profit decreases if output
increases.
If MR = MC, economic
profit decreases if output
changes in either
direction, so economic
profit is maximized.
The Firm’s Decisions in
Perfect Competition

In part (c) price is less than ATC and the firm
incurs an economic loss—economic profit is
negative and the firm does not even earn normal
profit.
The Firm’s Short-Run Supply
Curve
A perfectly competitive firm’s short-run supply
curve shows how the firm’s profit-maximizing
output varies as the market price varies, other
things remaining the same.


Because the firm produces the output at which
marginal cost equals marginal revenue, and
because marginal revenue equals price, the firm’s
supply curve is linked to its marginal cost curve.
But there is a price below which the firm produces
nothing and shuts down temporarily.
Temporary Plant Shutdown
If the price is less than the minimum
average variable cost, the firm shuts
down temporarily
and incurs a loss equal to total fixed
cost..
短期如關門q=0,
損失為FC(沉沒成本)
是否營運?
比較營運損失是否 小於關門損失FC
營運：q > 0π= TR – TC
π１= TR – TC = TR – ( TVC + TFC)
=(TR-TVC)-TFC
不營運：q = 0
π２= - TC = - TFC
營運：
πQ>0 >πQ=0 則營運
即 TR – (TVC + TFC) > - TFC
即 TR – TVC > 0
即 收益至少能支付變動成本
MC在AVC之上的部分為
完全競爭廠商之供給線
P=MR=MC決定產量
收益不能支付變動成本時產量=0
The Firm’s
shutdown point

If price equals
minimum average
variable cost, $17 in
this example, the firm
is indifferent between
producing nothing and
producing at the
shutdown point, T.
the firm’s short-run supply curve
If the price is $31, the
firm produces 10 sweaters
a day, the quantity at
which P = MC.
The blue curve in part (b)
traces.
The Firm’s supply curve

At a price equal to
minimum average
variable cost—the
shutdown price—the
industry supply curve
is perfectly elastic
because some firms
will produce the
shutdown quantity
and others will
produce zero.
產業的供給
個別廠商供給的水平加總
s
s1
9
16
s2
7
Output, Price, and Profit in
Perfect Competition
A Change in Demand

An increase in demand
brings a rightward shift
of the industry demand
curve: the price rises
and the quantity
increases.
short-run equilibrium in
Perfect Competition
a firm may earn an economic profit,
earn normal profit, or incur an economic
loss.
為什麼WTO取消出口補貼會引起
多國農民的反彈?
農產品同質性(homogeneity)很高
全球各類農產品供給者數量龐大
全球各類農產品消費者者數量龐大
價格資訊相當完全
接近完全競爭
廠商成本結構很重要
出口補貼(變動補貼):
降低農產品成本
p
MC
D
MC
未受補貼的ATC
S
P
受補貼的ATC
Q
q*’
q*
q
出口補貼(非變動補貼):
降低農產品成本
p
MC
D
S
未受補貼的ATC
P
受補貼的ATC
Q
q* q*’
q
Long-Run Adjustments
In the long run, the firm may:


Enter or exit an industry
Change its plant size
Entry and Exit
New firms enter an industry in which
existing firms earn an economic profit.
 Firms exit an industry in which they incur
an economic loss.

Output, Price, and Profit in
Perfect Competition
As new firms enter
an industry, industry
supply increases.
 The industry supply
curve shifts
rightward.
The price falls, the
quantity increases, and the
economic profit of each
firm decreases.

Output, Price, and Profit in
Perfect Competition


As firms exit an
industry, industry
supply decreases.
The industry supply
curve shifts leftward.
The price rises, the
quantity decreases, and
the economic profit of
each firm increases.
Changes in Plant Size
Firms change their plant size whenever
doing so is profitable.
 If average total cost exceeds the minimum
long-run average cost, firms change their
plant size to lower costs and increase
profits.

Change Plant Size
to increase π

But if the LRAC curve is sloping downward at the
current output, the firm can increase profit by
expanding the plant.
Output, Price, and Profit in
Perfect Competition

As the plant size increases, short-run supply
increases, the price falls, and economic profit
decreases.
Output, Price, and Profit in
Perfect Competition

Long-run equilibrium occurs when the firm is
producing at the minimum long-run average cost
and earning zero economic profit.
Long-Run Equilibrium
Economic profit is zero, so firms neither
enter nor exit the industry.
 Long-run
average cost is at its minimum, so
firms don’t change their plant size.
Changing Tastes 1
(消費者偏好減低 但技術不變)
A Permanent Change in Demand

A decrease in demand shifts the demand curve
leftward. The price falls and the quantity decreases.
Changing Tastes 2
the fall in price puts the price below each firm’s
minimum average total cost and firms incur an
economic loss.
 Economic losses induce exit, which decreases
short-run supply and shifts the short-run
industry supply curve leftward.
 As industry supply decreases, the price rises
and the market quantity continues to decrease.

Changing Tastes 3

With a rising price, each firm that remains in the
industry increases production in a movement along the
firm’s marginal cost curve (short-run supply curve).
Changing Tastes 4

A new long-run equilibrium occurs when the price has
risen to equal minimum average total cost so that firms
do not incur economic losses, and firms no longer
leave the industry.
Changing Tastes 5


The main difference between the initial and new longrun equilibrium is the number of firms in the industry.
原先n0=Q0/q0, 現在n1= Q2/q0 廠商數目減少
Changing Tastes 6
In the new equilibrium, a smaller number of
firms produce the equilibrium quantity.
 僅有需求面改變時，最適規模未改變

A permanent increase in
demand




has the opposite effects to those just described.
An increase in demand shifts the demand curve
rightward. The price rises and the quantity
increases.
Economic profit induces entry, which increases
short-run supply and shifts the short-run industry
supply curve rightward.
As industry supply increases, the price falls and
the market quantity continues to increase.
Changing Tastes and
Advancing Technology


A new long-run equilibrium occurs when the price
has fallen to equal minimum average total cost so
that firms do not earn economic profits, and firms
no longer enter the industry.
The main difference between the initial and new
long-run equilibrium is the number of firms in the
industry. In the new equilibrium, a larger number of
firms produce the equilibrium quantity.
Long-Run Equilibrium
P = MC = AC
利潤為零，且在LRAC最低點
LRAC是完全競爭廠商的長期供給線
偏好和技術進步對
長期均衡的影響
External Economies and Diseconomies
The change in the long-run equilibrium
price following a permanent change in
demand depends on external economies
and external diseconomies.
 產業產量改變時，外在環境影響生產成本
 非單一廠商自己所能控制
 External economies (外部經濟)
 External diseconomies (外部不經濟)

External economies
(外部經濟)

are factors beyond the control of an
individual firm that lower the firm’s costs as
the industry output increases.
External diseconomies
(外部不經濟)

are factors beyond the control of a firm that
raise the firm’s costs as industry output
increases.
Constant cost

In the absence of external economies or
external diseconomies, a firm’s costs
remain constant as industry output
changes.
Changing Tastes and
Advancing Technology

in the absence of
external economies or
external diseconomies,
the price remains
constant when
demand increases.
external diseconomies

when external
diseconomies are
present, the price
rises when demand
increases.
external diseconomies




the market for defense goods like nuclear
submarines or stealth bombers would be an
example of external diseconomies.
If the government desired to contract with private
firms for a significant increase in the number of
these machines, many different firms might enter
the market,
raising the demand for scientists and engineers
with rare technical skills and expertise (unique
human capital).
The wages of these highly skilled workers would
increase, raising the cost per unit of production.
external economies
New York City’s financial districts, or
Silicon Valley’s high technology
industries.
 Sometimes close locational proximity
of mobile and abundant, highly
specialized laborers can decrease the
cost of doing business in that area,
resulting in firms experiencing falling
costs per unit of production.

external economies

Figure 11.11(c) shows
that when external
economies are present,
the price falls when
demand increases.
Technological Change
New technologies are constantly
discovered that lower costs.
 A new technology enables firms to produce
at a lower average cost and lower marginal
cost—firms’ cost curves shift downward.
 Firms that adopt the new technology earn
an economic profit.

Advancing Technology




New-technology firms enter and old-technology
firms either exit or adopt the new technology.
Industry supply increases and the industry supply
curve shifts rightward.
The price falls and the quantity increases.
Eventually, a new long-run equilibrium emerges in
which all the firms use the new technology, the
price has fallen to the minimum average total cost,
and each firm earns normal profit.
Effects of Advancing
Technology
The adjustment process as old-technology
firms exit or adopt the new technology and
new-technology firms enter can create
great changes in local geographic
prosperity.
 Some regions experience economic
decline while others experience economic
growth.

Competition and Efficiency
Efficient Use of Resources
Resources are used efficiently when no
one can be made better off without making
someone else worse off.
 This situation arises when marginal benefit
equals marginal cost.

Choices, Equilibrium, and
Efficiency
從社會的角度思考完全競爭均衡的效率
性：我們運用資源制製造產品，得到的
是什麼?
We can describe an efficient use of
resources in terms of the choices of
consumers and firms coordinated in
market equilibrium.
社會的利益面: 需求
We derive a consumer’s demand curve
by finding how the best (most valued by
the consumer) budget allocation
changes as the price of a good changes.
So consumers get the most value out of
their resources at all points along their
demand curves, which are also their
marginal benefit curves.
社會的付出面: 供給
We derive a competitive firm’s supply
curve by finding how the profit-maximizing
quantity changes as the price of a good
changes.
 So firms get the most value out of their
resources at all points along their supply
curves, which are also their marginal cost
curves.

Competition and Efficiency
In competitive equilibrium, the quantity
demanded equals the quantity supplied, so
marginal benefit equals marginal cost.
 All gains from trade have been realized.

Competition and Efficiency



efficient outcome in a
perfectly competitive
industry.
Along the demand
curve D = MB the
consumer is efficient.
Along the supply
curve S = MC the
producer is efficient.
Competition and Efficiency
If the quantity
produced were Q0,
marginal benefit B0
would exceed
marginal cost C0 and
everyone would be
better off if production
increased.
If the quantity produced
were Q*, marginal benefit
would equal marginal cost
at P*.
This outcome is efficient.

Competition and Efficiency

The quantity Q* and
price P* are the
competitive
equilibrium values.
The consumer gains the
consumer surplus,
and the producer gains the
producer surplus.
市場的效率 1
以價格作為資源分配的指標
 使資源留在最適合自身(賺取最高利潤，得
到最高效用)的市場
 Competitive equilibrium is efficient only if
there are no external benefits or costs.
 市場的價格機能

市場的效率 2
Competitive equilibrium is efficient only if
there are no external benefits or costs.
 市場可能失靈
 External benefits (外部成本) are benefits
that accrue to people other than the buyer
of a good.
 External costs (外部效益) are costs that
are borne not by the producer of a good or
service but by someone else.

Efficiency of Perfect
Competition
Three main obstacles to achieving
efficiency in resource allocation are:
 Monopoly
 Public goods
 External costs and benefits

Monopoly
restricts output to increase price and profit—
Chapter 12 examines monopoly.
Public goods
Public goods are goods from which
everyone benefits but no one would
willingly pay, so a competitive market
would produce a quantity below the
efficient level—Chapter 16 examines
public goods.
External costs and benefits

External costs or benefits mean that
demand curves do not measure all the
benefits and cost curves do not measure
all the costs, so the competitive market
might produce too much or too little—
Chapter 18 examines externalities.
市場的特性I
完全競爭市場
定義：一產業由許多
同質(homogeneous)小廠商組成，供應同質產
品，
享有完全資訊(perfect information)，
廠商都是價格的接受者(price-taker)，
自由進出市場(no entry barrier)，且廠商數目
極多．
例：稻米，
當中廠商的行為：price-taker～決定產量
最適產量的決定MR = MC
MR = AR = P，
是否保証利潤 > 0?
是否一旦賠錢便立即關廠？ NO.
殺頭生意有人做，賠本生意沒人做？
短期如關門FC沉沒成本為損失
比較損失是否 < FC
長期如關門處分資本，< = FC
營運：Q > 0π= TR – TC
π１= TR – TC = TR – ( TVC + TFC)
不營運：Q = 0
π２= - TC = - TFC
營運：
則πQ>0 >πQ=0
即 TR – (TVC + TFC) > - TFC
即 TR – TVC > 0
即 收益至少能支付變動成本
MC在AVC之上的部分為完全競爭
廠商之供給線
長期與短的差別
短期間各廠商可能有利潤 > or < 0之狀況
(成本決定利潤)
但長期間，加入 S ↑(利潤>0)，且完
全資訊，所以有加入者
退出 S ↓(利潤<0)
長期均衡
P = MC = AC
利潤為零，且在LRAC最低點
LRAC是長期供給線
完全競爭與效率
在長期中，每一廠商在LRAC之最低點，
因此為最有效率的生產效率
完全競爭市場之所以能使資源有效率的
分配，是建立在特定假設之下的結果
其中市場的完全資訊，產品的同質性在
現實生活中往往達不到故而劣幣驅逐良
幣的狀況並不罕見
例如
beta被VHS取代
 IBM (compatible)在市佔率上遠超過Apple
