不完全競爭

為何有許多檳榔攤？客人似乎不多，如何賺取利潤？為何 Coca Cola, Nike ，泛亞要拍那麼多廣告？金價天天在變，為什麼有些東西價格卻很少改變？

米酒 VS 青菜

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【不完全競爭市場理論】主要是由英國的羅賓遜夫人（ Robinson ）與美國的秦伯霖（ Chamberlin ）分別發展出來的。由於在實際的經濟社會中，廠商對價格多多少少具有決定能力，所面對的市場既非完全開放（如：完全競爭市場），也不是全然封閉（如：完全獨占市場），因此，實際經濟社會的市場形態多為「不完全競爭市場」。

不完全競爭市場包含了「獨占性競爭市場」與「寡占市場」兩種基本形態，兩者的相同點為：個別廠商對價格都具有影響力；而相異點在於獨占性競爭市場的廠商人數眾多，而寡占市場通常由少數幾個廠商控制整個產業。

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龔斷性競爭Monopolistic Competition

廠商數目多，買者多，每個人都只有很少的占有率自由進出完全資訊Firms compete on product quality, price, and marketing異質性產品：如洗髮精、泡麵、蔥油餅

PC War Games Each PC maker tells us that they have the best

product at the best price. Just two big chip makers produce almost all the

processor and memory chips in our PCs. Firms in these markets are neither price takers like

those in perfect competition, nor are they protected from competition by barriers to entry like a monopoly.

How do such firms choose the quantity to produce and price?

Monopolistic CompetitionMonopolistic competition is a market

with the following characteristics: A large number of firms. Each firm produces a differentiated

product. Firms compete on product quality, price,

and marketing. Firms are free to enter and exit the

industry.

Large Number of Firms implies

Each firm has only a small market share and therefore has limited market power to influence the price of its product.

Each firm is sensitive to the average market price, but no firm pays attention to the actions of the other, and no one firm’s actions directly affect the actions of other firms.

Collusion, or conspiring to fix prices, is impossible.

Product Differentiation

each firm makes a product that is slightly different from the products of competing firms.

Competing on Quality, Price, and Marketing

Quality includes design, reliability, and service. Because firms produce differentiated products,

each firm has a downward-sloping demand curve for its own product.

But there is a tradeoff between price and quality. Differentiated products must be marketed using

advertising and packaging.

Entry and Exit

There are no barriers to entry in monopolistic competition, so firms cannot earn an economic profit in the long run.

Examples of Monopolistic Competition

The red bars refer to the 4 largest firms.

Green is the next 4.

Blue is the next 12.

Short-Run Economic Profit

A firm that has decided the quality of its product and its marketing program produces the profit maximizing quantity at which its marginal revenue equals its marginal cost (MR = MC).

Price is determined from the demand curve for the firm’s product and is the highest price the firm can charge for the profit-maximizing quantity.

　獨占性競爭市場的短期均衡9-2

( 一 ) 獨占性競爭廠商所面對的需求曲線一條由左上方向右下方延伸的需求曲線。獨占性競爭廠商所面對的需求曲線較獨占廠商平坦些。獨占性競爭廠商的獨占性愈強，其所面對的曲線愈陡峭，反之則愈平坦。

Output and Price in Monopolistic Competition

It operates much like a single-price monopolist.

The firm produces the quantity at which price equals marginal cost and sells that quantity for the highest possible price.

It earns an economic profit (as in this example) when P > ATC.

獨占性競爭市場的長期均衡Zero Economic Profit In the long run, economic profit induces entry. And entry continues as long as firms in the

industry earn an economic profit—as long as (P > ATC).

In the long run, a firm in monopolistic competition maximizes its profit by producing the quantity at which its marginal revenue equals its marginal cost, MR = MC.

長期均衡P = AC利潤為零，但不在 LRAC 最低點

　獨占性競爭市場的長期均衡9-2

D = A RM R

S M C L M C L A CS A C

E

E '


As firms enter the industry, each existing firm loses some of its market share. The demand for its product decreases and the demand curve for its product shifts leftward.

The decrease in demand decreases the quantity at which MR = MC and lowers the maximum price that the firm can charge to sell this quantity.

Price and quantity fall with firm entry until P = ATC and firms earn zero economic profit.


If firms incur an economic loss, firms exit to restore the long-run equilibrium just described.

Monopolistic Competition and Efficiency

Firms in monopolistic competition are inefficient and operate with excess capacity.

Excess Capacity超額產能理論AC 最低點是最適產量，而獨占性競爭長期均衡卻是在切點，故通常有產能的浪費。

Excess Capacity

是否應鼓勵所有公司合併？產量不變而總成本可能減少消費者的選擇會減少很多的檳榔攤、小吃店，使顧客較為方便　　　

excess capacity

Because price equals the marginal benefit, marginal cost is less than marginal benefit.

Underproduction in monopolistic competition creates deadweight loss.

capacity output A firm’s capacity output is

the output at which average total cost is at its minimum.

At the long-run profit maximizing output, price equals average total cost.

excess capacity If MC < ATC, then

the ATC curve is falling.

With falling ATC, output is less than capacity output.

Goods are not produced at the minimum unit cost of production in the long run.

Product Development and Marketing

Innovation and Product DevelopmentTo keep earning an economic profit, a firm

in monopolistic competition must be in a state of continuous product development.

New product development allows a firm to gain a competitive edge, if only temporarily, before competitors imitate the innovation.

1. 就生產效率觀點而言獨占性競爭廠商的長期均衡點並非長期平均成本的最低點，因此不是最適生產規模（小於最適規模），表示廠商沒有充分利用資源。 2. 就資源配置觀點而言當 P=MC 時，資源達到最佳配置效率，但在獨占性競爭之情形下，依據 MR=MC 均衡條件，得出 P>MC ，故價格偏高，產量偏低。

3. 就消費福利觀點而言獨占性競爭場商的產品具有差異性，可以滿足個

別消費者的偏好，增進消費者福利，但是消費者必須付出較高的價格是其缺點。

Innovation Innovation is costly, but it increases total revenue. Firms pursue product development until the marginal

revenue from innovation equals the marginal cost of innovation.

Production development may benefit the consumer by providing an improved product, or it may only create the appearance of a change in product quality.

Regardless of whether a product improvement is real or imagined, its value to the consumer is its marginal benefit, which is the amount the consumer is willing to pay for it.

Marketing行銷和廣告的作用A firm’s marketing program uses

advertising and packaging as the two principal methods to market its differentiated products to consumers.

Firms in monopolistic competition incur heavy marketing and advertising expenditures to enhance the perception of quality differences between their product and rival products. These costs make up a large portion of the price for the product.


Cleaning supplies and toys top the list at almost 15 percent.

Selling Costs and Total Costs

Selling costs, like advertising expenditures, fancy retail buildings, etc. are fixed costs. Average fixed costs decrease as production

increases, so selling costs increase average total costs at any given level of output but do not affect the marginal cost of production.

Selling efforts such as advertising are successful if they increase the demand for the firm’s product.


With advertising, the firm produces 130 units of output at an average total cost of $160.

advertising has a short run effect

Economic profit leads to entry, which decreases the demand for each firm’s product in the long run.

To the extent that advertising and selling costs provide consumers with information and services that they value more highly than their cost, these activities are efficient.

廣告Why not Perfect Competition firm?

相對市場非常少，故無需要產品 identical 廣告增加成本，卻可能導向其他廠商

OligopolyOligopoly is a market in which a small

number of firms compete. In oligopoly, the quantity sold by one firm

depends on the firm’s own price and the prices and quantities sold by the other firms.

The response of other firms to a firm’s price and output influence the firm’s profit-maximizing decision.

寡占市場的特質互相牽制，互相依賴

寡占市場是由少數幾家廠商控制整個產業，每家廠商的行動都會影響到其他廠商的利益，因此寡占廠商彼此間會互相牽制、也相互依賴。

1. The Kinked Demand Curve Model拗折的需求線

In the kinked demand curve model of oligopoly, each firm believes that if it raises its price, its competitors will not follow, but if it lowers its price all of its competitors will follow.

拗折需求曲線又稱「扭結需求曲線」，此理論主要是用來解釋寡占廠商價格僵固的現象，由美國經濟學家史威吉（ P. M. Sweezy ）於 1939年所提出。根據該模型認為，寡占廠商的市場需要曲線，不同於其他市場的生產者，而具有特殊形態，由於此一特殊形態，使得寡占市場的價格相當穩定，不易變化。

拗折的需求線 (sticky price)價格僵硬化模型基本假設：跟跌不跟漲即指：當某一寡占廠商提高價格時，其它廠商不會跟著抬高價格（此為不跟漲），可是當某一寡占廠商降低價格時，其它廠商們擔心市場會被掠奪，故會馬上調低價格（此為跟跌）。

即使 MC 有所改變，價格不變 ( 穩定的價格取向 )

OligopolyThe demand

curve that a firm believes it faces has a kink at the current price and quantity.

Oligopoly Above the kink,

demand is relatively elastic because all other firm’s prices remain unchanged.

Below the kink, demand is relatively inelastic because all other firm’s prices change in line with the price of the firm shown in the figure.

穩定的價格Fluctuations in MC that remain within the discontinuous portion of the MR curve leave the profit-maximizing quantity Q and price P unchanged.

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(三 ) 拗折的需要曲線

MR

A

B

C

D

E

DA

DB

DA

MRB MRA

DB

KP0

Q0

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(四 ) 拗折需求曲線解釋價格的僵固性由於廠商間的競爭策略為「跟跌不跟漲」，所以需求曲線有拗折點的存在，故其對應 AKB 需求曲線的邊際收益曲線 MR ，會在拗折點所決定的產量下有斷折的情形，稱為邊際收益缺口 (marginal revenue gap) 。

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(五 ) 結論由拗折的需求曲線可知，當寡占廠商建立某價格後，若MC 變動不大，則其價格不會改變，造成了價格僵固性（ price rigidity ）的現象。在實際社會中不乏有這方面的例子，如汽車、電視等產品的價格就不會像日常生活中的蔬菜水果或魚類的價格經常在改變，這主要是因為廠商們對於價格的設定，除非不得已否則都會儘量採按兵不動的策略。

OligopolyThe beliefs that generate the kinked

demand curve are not always correct and firms can figure out this fact

If MC increases enough, all firms raise their prices and the kink vanishes.

A firm that bases its actions on wrong beliefs doesn’t maximize profit.

2. Dominant Firm Oligopoly 價格領袖In a dominant firm oligopoly, there is one large firm that has a significant cost advantage over many other, smaller competing firms. The large firm operates as a monopoly, setting its

price and output to maximize its profit. The small firms act as perfect competitors, taking

as given the market price set by the dominant firm.

寡占市場中的廠商可能為了避免獨自訂價的麻煩，以及所訂價格可能引起競爭者的不良反應等因素，往往不自行訂價，而是參考某一廠商的價格，再決定自己的價格。被其他廠商作為價格依據的廠商，稱為價格領袖或價格領導者( price leader ) 。而其他追隨此價格領袖的廠商可稱為價格跟隨者 (price followers) 。

Dominant Firm At a price of $1.50, the 10 small firms produce the quantity

demanded. At this price, the large firm would sell nothing.

S10

But if the price was $1.00, the 10 small firms would supply only half the market, leaving the rest to the large firm.

Oligopoly The demand curve for the large firm’s output is the

curve XD on the right.

The large firm can set the price and receives a marginal revenue that is less than price along the curve MR.

The large firm maximizes profit by setting MR = MC. The profit-maximizing quantity for the large firm is 10 units. The

price charged is $1.00. The small firms take this price and supply the rest of the

quantity demanded.

A dominant firm oligopoly can arise only if one firm has lower costs than

the others

In the long run, such an industry might become a monopoly as the large firm buys up the small firms and cuts costs.

3.Oligopoly GamesGame theory is a tool for studying

strategic behavior, which is behavior that takes into account the expected behavior of others and the mutual recognition of interdependence.

What Is a Game?All games share four features: Rules Strategies Payoffs Outcome

The Prisoners’ Dilemma 1 The prisoners’ dilemma game illustrates the four

features of a game. The rules describe the setting of the game, the

actions the players may take, and the consequences of those actions.

In the prisoners’ dilemma game, two prisoners (Art and Bob) have been caught committing a petty crime.

Each is held in a separate cell and cannot communicate with the other.

The Prisoners’ Dilemma 2Each is told that both are suspected of

committing a more serious crime. If one of them confesses, he will get a 1-year

sentence for cooperating while his accomplice get a 10-year sentence for both crimes.

If both confess to the more serious crime, each receives 3 years in jail for both crimes.

If neither confesses, each receives a 2-year sentence for the minor crime only.

strategiesIn game theory, strategies are all the possible actions of each player.Art and Bob each have two possible actions: Confess to the larger crime Deny having committed the larger crime

Because there are two players and two actions for each player, there are four possible outcomes: Both confess Both deny Art confesses and Bob denies Bob confesses and Art denies

payoff matrixEach prisoner can work out what happens to

him—can work out his payoff—in each of the four possible outcomes.

We can tabulate these outcomes in a payoff matrix.

A payoff matrix is a table that shows the payoffs for every possible action by each player for every possible action by the other player.

Oligopoly Games

Payoff Matrix

Nash equilibrium If a player makes a rational choice in

pursuit of his own best interest, he chooses the action that is best for him, given any action taken by the other player.

If both players are rational and choose their actions in this way, the outcome is an equilibrium called Nash equilibrium—first proposed by John Nash.

Bob’s view of the world

Art’s view of the world

Equilibrium

An Oligopoly Price-Fixing Game

A game like the prisoners’ dilemma is played in duopoly.A duopoly is a market in which there are

only two producers that compete.Duopoly captures the essence of oligopoly.

Oligopoly Games This industry is a natural duopoly. Two firms can meet the market demand at the least cost.

Oligopoly Games How does this market work? What is the price and quantity produced in equilibrium?

collusive agreementSuppose that the two firms enter into a

collusive agreement.A collusive agreement is an agreement

between two (or more) firms to restrict output, raise price, and increase profits.

Such agreements are illegal in the United States and are undertaken in secret.

Firms in a collusive agreement operate a cartel.

Oligopoly GamesThe possible strategies are:

ComplyCheat

there are four possible outcomes:Both comply Both cheatTrick complies and Gear cheatsGear complies and Trick cheats

Both comply The firms maximize economic profit by producing the

quantity at which MCI =(MC1+MC2)= MR.

Both comply Each firm agrees to produce 2,000 units and each firm

shares the maximum economic profit.

Cheat 的誘因來自於潛在利潤 When each firm produces 2,000 units, the price is

greater than the firm’s marginal cost, so if one firm increased output, its profit would increase.

when one firm cheats and increases its output to 3,000 units. Industry output rises to 5,000 and the price falls.

一方違反約定，老實人吃虧 The complier incurs an economic loss. The cheat earns an increased economic profit.

both firms cheat Industry output is 6,000 units, the price falls, and

both firms earn zero economic profit—the same as in perfect competition.

Payoff Matrix

Trick’s view of the world

Gear’s view of the world

Equilibrium

Nash equilibriumThe Nash equilibrium is where both firms

cheat.The quantity and price are those of a

competitive market, and the firms earn normal profit.

聯手標購中華電信國泰富邦金雙贏國泰、富邦繼競逐北銀、世華銀股權後首度攜手合作原本外界以為會互相競標的國泰、富邦採取聯手投標策略，以每股 50.3 元得標前 2 次釋股價格 :$104 ， $57.57得標集團 : 美商摩根大通代表國泰、富邦、台灣固網、台灣大哥大等競標

Other Oligopoly Games

Advertising and R & D games are also prisoners’ dilemmas.

Repeated Games and Sequential Games

A Repeated Duopoly Game If a game is played repeatedly, it is possible for

duopolists to successfully collude and earn a monopoly profit.

If the players take turns and move sequentially (rather than simultaneously as in the prisoner’s dilemma), many outcomes are possible.

In a repeated prisoners’ dilemma duopoly game, additional punishment strategies enable the firms to comply and achieve a cooperative equilibrium, in which the firms make and share the monopoly profit.


One possible punishment strategy is a tit-for-tat strategy 一報還一報 , in which one player cooperates this period if the other player cooperated in the previous period but cheats in the current period if the other player cheated in the previous period.

A more severe punishment strategy is a trigger strategy in which a player cooperates if the other player cooperates but plays the Nash equilibrium strategy forever thereafter if the other player cheats.


Price wars might result from a tit-for-tat strategy where there is an additional complication—uncertainty about changes in demand.

A fall in demand might lower the price and bring forth a round of tit-for-tat punishment.


A Sequential Entry Game in a Contestable Market In a contestable market—a market in

which firms can enter and leave so easily that firms in the market face competition from potential entrants—firms play a sequential entry game.


In the first stage, Agile decides whether to set the monopoly price or the competitive price.


In the second stage, Wanabe decides whether to enter or stay out.


In the equilibrium of this entry game, Agile sets a competitive price and earns a normal profit to keep Wanabe out.

A less costly strategy is limit pricing, which sets the price at the highest level that is consistent with keeping the potential entrant out.

寡占Oligopoly

市場中只有少數的廠商，其中至少有幾家廠商可影響市場價格同質寡占 , 異質寡占大小

Oligopoly 理論模型分析：競爭對手、策略、價格、產量的選擇interdependence ，互動性很高strategic interaction 策略性互動

卡特爾 Cartel ，廠商聯合就 P & Q 等勾結以求獲得獨占利潤被很多經濟學家認為是最糟的產業，因為有獨占的 P & Q ，但卻未勿有效率 ( 規模經濟 ) ，所以公開勾結在許多國家是違法的

Price-leadershipPrice-war

1.Sales maximization

因經理並不擁有公司，“大公司”比“高利潤”給予經理人報酬

Game theory賽局理論假設對手決策方式：策略、計劃Pay off matrix 　結果的估計如何選擇：

1. Nash 均衡：根據對手策略，採用自己結果最佳的策略2.悲觀地假設最壞的會發生，在對手作最大打擊中選擇最佳結果 Maximin criterion

雖然 non-profit comp mkt 有許多缺點，但如市場進出自由、成本很低，則潛在競爭者足使現有廠商不致太囂張

市場結構分類市場結構基本特徵內涵例子完全競爭價格接受者

自由進出廠商數很多，訊息充分，產品同質

生產稻米的農民

獨占性競爭異質產品進出容易有限的價格決定者

個別廠商仍有部分的價格決定力，產品異質零售業、紡織、餐館

寡占彼此牽制，進出困難，價格決定者訂價決策彼此牽制，產品同質或異質

百貨公司，水泥，電視台

獨占只此一家價格決定者

沒有近似的替代品水電，郵政

不完全競爭

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