1. Imperfect Competition
Chapter 15
Imperfect Competition

2. Chapter Overview
● Monopolistic competition
Market in which firms can enter freely, each producing its own brand or version of a differentiated product.
● Oligopoly
Market in which only a few firms compete with one another, and entry by new firms is impeded.
● Cartel
Market in which some or all firms explicitly collude, coordinating prices and output levels to maximize joint profits.

3. Market Structures Four Key Dimensions • The number of buyers
• The number of sellers
• The number of buyers
• Entry conditions
• The degree of product differentiation

4. Example: Restaurants, Local markets for doctors
Chamberlinian Monopolistic Competition
Market Structure
Many Buyers
Many Sellers
Free entry and Exit
Product Differentiation
When firms have differentiated products, they each face downward-sloping demand for their product because a small change in price will not cause ALL buyers to switch to another firm's product.
Example: Restaurants, Local markets for doctors

5. Monopolistic Competition
A monopolistically competitive market has two key characteristics:
Firms compete by selling differentiated products that are highly substitutable for one another but not perfect substitutes.
i.e: the cross-price elasticities of demand are large but not infinite.
There is free entry and exit: It is relatively easy for new firms to enter the market with their own brands and for existing firms to leave if their products become unprofitable.

6. Equilibrium in the Short Run
Because the firm is the only producer of its brand, it faces a downward-sloping demand curve.
Price exceeds marginal cost and the firm has monopoly power.
In the short run, price also exceeds average cost, and the firm earns profits shown by the yellow-shaded rectangle.

7. A MONOPOLISTICALLY COMPETITIVE FIRM IN THE SHORT AND LONG RUN
In the long run, these profits attract new firms with competing brands.
The firm’s market share falls, and its demand curve shifts downward.
In long-run equilibrium, P = ATC, so the firm earns zero profit even though it has some degree of market power.

8. Under perfect competition, in the long run, P = AC = MC.
COMPARISON OF MONOPOLISTICALLY COMPETITIVE EQUILIBRIUM AND PERFECTLY COMPETITIVE EQUILIBRIUM
Under perfect competition, in the long run, P = AC = MC.
The demand curve facing the firm is horizontal, so the zero-profit point occurs at the point of minimum average cost.

9. COMPARISON OF MONOPOLISTICALLY COMPETITIVE EQUILIBRIUM AND PERFECTLY COMPETITIVE EQUILIBRIUM
Under monopolistic competition, P > MC. Thus there is a deadweight loss, as shown by the yellow-shaded area.
The demand curve is downward-sloping, so the zero profit point is to the left of the point of minimum average cost.
In both types of markets, entry occurs until profits are driven to zero.

10. Is monopolistic competition then a socially undesirable market structure that should be regulated? The answer is NO for two reasons:
1. In most monopolistically competitive markets, monopoly power is small.
Usually enough firms compete, with brands that are sufficiently substitutable, so that no single firm has much monopoly power.
Any resulting deadweight loss will therefore be small.
And because firms’ demand curves will be fairly elastic, average cost will be close to the minimum.

11. Is monopolistic competition then a socially undesirable market structure that should be regulated? The answer is NO for two reasons:
2. Any inefficiency must be balanced against an important benefit from monopolistic competition: product diversity.
Most consumers value the ability to choose among a wide variety of competing products and brands that differ in various ways.
The gains from product diversity can be large and may easily outweigh the inefficiency costs resulting from downward-sloping demand curves.

12. Oligopoly Assumptions: Many Buyers and Few Sellers
Each firm faces downward-sloping demand because each is a large producer compared to the total market size
There is no one dominant model of oligopoly. We will review several.

13. Oligopoly The products may or may not be differentiated
Only a few firms account for most or all of total production.
In some cases, some or all firms earn substantial profits over the long run because barriers to entry make it difficult or impossible for new firms to enter.
Examples of oligopolistic industries include automobiles, steel, aluminum, petrochemicals, electrical equipment, and computers.

14. Oligopoly Factors acting as barriers of entry to the market:
1) Scale economies may make it unprofitable for more than a few firms to coexist in the market;
2) Patents or access to a technology may exclude potential competitors;
3) The need to spend money for name recognition and market reputation may discourage entry by new firms.
In addition, firms may take strategic actions to deter entry.
Managing an oligopolistic firm is complicated because pricing, output, advertising, and investment decisions involve important strategic considerations, which can be highly complex.

15. Equilibrium in the Oligopoly
In an oligopolistic market, a firm sets price or output based partly on strategic considerations regarding the behavior of its competitors.
When a market is in equilibrium, firms are doing the best they can and have no reason to change their price or output.

16. NASH EQUILIBRIUM
● Nash equilibrium Set of strategies or actions in which each firm does the best it can, given its competitors’ actions.
● Duopoly Market in which two firms compete with each other.

17. Cournot Oligopoly Assumptions Homogeneous Products Simultaneous
Firms set outputs (quantities)*
Homogeneous Products
Simultaneous
Non-cooperative
*Definition: In a Cournot game, each firm sets its output (quantity) taking as given the output level of its competitor(s), so as to maximize profits.
Price adjusts according to demand.
Residual Demand: Firm i's guess about its rival's output determines its residual demand.

18. Residual Demand
Definition: The relationship between the price charged by firm i and the demand firm i faces is firm is residual demand
In other words, the residual demand of firm i is the market demand minus the amount of demand fulfilled by other firms in the market: Q1 = Q - Q2

19. Residual Demand Residual Marginal Revenue when q2 = 10
Price
Residual Marginal Revenue when q2 = 10
10 units
Residual Demand when q2 = 10 MC
Demand
Quantity
q1*

20. The Cournot Model FIRM 1’S OUTPUT DECISION
Firm 1’s profit-maximizing output depends on how much it thinks that Firm 2 will produce.
If it thinks Firm 2 will produce nothing, its demand curve is D1(0), is the market demand curve. The corresponding MR1(0), intersects Firm 1’s MC1 at an output of 50 units.
If Firm 1 thinks that Firm 2 will produce 50 units, its demand curve, D1(50), is shifted to the left by this amount.
Profit maximization now implies an output of 25 units. 5 75
Finally, if Firm 1 thinks that Firm 2 will produce 75 units, Firm 1 will produce only 12.5 units.

21. REACTION CURVES AND COURNOT EQUILIBRIUM
● Relationship between a firm’s profit-maximizing output and the amount it thinks its competitor will produce.
Firm 1’s reaction curve shows how much it will produce as a function of how much it thinks Firm 2 will produce. (The xs at Q2 = 0, 50, and 75 correspond to the examples.)
Firm 2’s reaction curve shows its output as a function of how much it thinks Firm 1 will produce.
In Cournot equilibrium, each firm correctly assumes the amount that its competitor will produce and thereby maximizes its own profits. Therefore, neither firm will move from this equilibrium.

22. Profit Maximization
Profit Maximization: Each firm acts as a monopolist on its residual demand curve, equating MRr to MC.
MRr = MC
Best Response Function:
The point where (residual) MR = MC gives the best response of firm i to its rival's (rivals') actions.
For every possible output of the rival(s), we can determine firm i's best response.
The sum of all these points makes up the best response (reaction) function of firm i.

23. COURNOT EQUILIBRIUM
● Equilibrium in the Cournot model in which each firm correctly assumes how much its competitor will produce and sets its own production level accordingly.
Cournot equilibrium is an example of a Nash equilibrium (and thus it is sometimes called a Cournot-Nash equilibrium).
In a Nash equilibrium, each firm is doing the best it can given what its competitors are doing.
As a result, no firm would individually want to change its behavior.
In the Cournot equilibrium, each firm is producing an amount that maximizes its profit given what its competitor is producing, so neither would want to change its output.

24. If the firms collude and share profits equally, each will produce 7.5.
DUOPOLY EXAMPLE
The demand curve is P = 30 − Q, and both firms have zero marginal cost. In Cournot equilibrium, each firm produces 10.
The collusion curve shows combinations of Q1 and Q2 that maximize total profits.
If the firms collude and share profits equally, each will produce 7.5.
● Also shown is the competitive equilibrium, in which P = MC and profit is zero.

25. Bertrand Oligopoly (homogeneous product)
Assumptions:
Firms set price*
Homogeneous product
Simultaneous
Non-cooperative
*Definition: In a Bertrand oligopoly, each firm sets its price, taking as given the price(s) set by other firm(s), so as to maximize profits.

26. Setting Price
Homogeneity implies that consumers will buy from the low-price seller.
Further, each firm realizes that the demand that it faces depends both on its own price and on the price set by other firms
Specifically, any firm charging a higher price than its rivals will sell no output.
Any firm charging a lower price than its rivals will obtain the entire market demand.

27. Equilibrium
If we assume no capacity constraints and that all firms have the same constant average and marginal cost of c then:
For each firm's response to be a best response to the other's each firm must undercut the other as long as P> MC
Where does this stop? P = MC (!)

28. Price Competition with Homogeneous Products—The Bertrand Model
● Oligopoly model in which firms produce a homogeneous good, each firm treats the price of its competitors as fixed, and all firms decide simultaneously what price to charge.
P = 30 – Q and let MC1 = MC2 = $3
Q1 = Q2 = 9, and in Cournot equilibrium, the market price is $12, so that each firm makes a profit of $81.

29. • Residual Demand Curve – Price Setting Price Market Demand
Residual Demand Curve (thickened line segments) •
Quantity

30. Price Competition with Homogeneous Products—The Bertrand Model
Now suppose that these two duopolists compete by simultaneously choosing a price instead of a quantity.
Nash equilibrium in the Bertrand model results in both firms setting price equal to marginal cost: P1 = P2 = $3.
Then industry output is 27 units, of which each firm produces 13.5 units, and both firms earn zero profit.
In the Cournot model, because each firm produces only 9 units, the market price is $12.
Now the market price is $3.
In the Cournot model, each firm made a profit;
In the Bertrand model, the firms price at marginal cost and make no profit.

31. Stackelberg Model of Oligopoly
A situation in which one firm acts as a quantity leader, choosing its quantity first, with all other firms acting as followers.
Call the first mover the “leader” and the second mover the “follower”.
The second firm is in the same situation as a Cournot firm: it takes the leader’s output as given and maximizes profits accordingly, using its residual demand.
The second firm’s behavior can, then, be summarized by a Cournot reaction function.

32. Dominant Firm Markets
A single company with an overwhelming market share (a dominant firm) competes against many small producers (competitive fringe), each of whom has a small market share.
Limit Pricing – a strategy whereby the dominant firm keeps its price below the level that maximizes its current profit in order to reduce the rate of expansion by the fringe.

33. The Dominant Firm Model
● Dominant firm Firm with a large share of total sales that sets price to maximize profits, taking into account the supply response of smaller firms.
PRICE SETTING BY A DOMINANT FIRM
The dominant firm sets price, and the other firms sell all they want at that price. The dominant firm’s demand curve, DD, is the difference between market demand D and the supply of fringe firms SF . The dominant firm produces a quantity QD at the point where its marginal revenue MRD is equal to its marginal cost MCD.
The corresponding price is P*. At this price, firms sell QF so that total sales equal QT.

34. Assumptions: Firms set price* Differentiated product Simultaneous
Bertrand Competition – Differentiated
Assumptions:
Firms set price*
Differentiated product
Simultaneous
Non-cooperative
*Differentiation means that lowering price below your rivals' will not result in capturing the entire market, nor will raising price mean losing the entire market so that residual demand decreases smoothly

35. Price Competition with Differentiated Products
Suppose each of two duopolists has fixed costs of $20 but zero variable costs, and that they face the same demand curves:
Firm 1’s demand:
Firm 2’s demand:
CHOOSING PRICES
Firm 1’s profit:
Firm 1’s profit maximizing price:
Firm 1’s reaction curve:
Firm 2’s reaction curve:

36. NASH EQUILIBRIUM IN PRICES
Here two firms sell a differentiated product, and each firm’s demand depends both on its own P and on its competitor’s P. The two firms choose their Ps at the same time, each taking its competitor’s P as given.
Firm 1’s reaction curve gives its profit-maximizing P as a function of the P that Firm 2 sets, and similarly for Firm 2.
The Nash equilibrium is at the intersection of the two reaction curves: When each firm charges a P of $4, it is doing the best it can given its competitor’s P and has no incentive to change P.
Also shown is the collusive equilibrium: If the firms cooperatively set price, they will choose $6.
The firms have the same costs, so they will charge the same price P. Total profit is given by : πT = π1 + π2 = 24P – 4P2 + 2P2 − 40 = 24P − 2P2 − 40.
This is maximized when πT/P = 0. πT/P = 24 − 4P, so the joint profit-maximizing P is
P = $6. Each firm’s profit is therefore
π1 = π2 = 12P − P = 72 − 36 − 20 = $16

37. Competition versus Collusion
In our example, there are two firms, each of which has fixed costs of $20 and zero variable costs. They face the same demand curves:
Firm 1’s demand:
Firm 2’s demand:
We found that in Nash equilibrium each firm will charge a price of $4 and earn a profit of $12, whereas if the firms collude, they will charge a price of $6 and earn a profit of $16.
So if Firm 1 charges $6 and Firm 2 charges only $4, Firm 2’s profit will increase to $20. And it will do so at the expense of Firm 1’s profit, which will fall to $4.

38. Equilibrium
Equilibrium occurs when all firms simultaneously choose their best response to each others' actions.
Graphically, this amounts to the point where the best response functions cross.

39. Equilibrium Notice That:
Profits are positive in equilibrium since both prices are above marginal cost!
Even if we have no capacity constraints, and constant marginal cost, a firm cannot capture all demand by cutting price.

40. Cournot, Bertrand, and Monopoly Equilibriums
A perfectly collusive industry takes into account that an increase in output by one firm depresses the profits of the other firm(s) in the industry.
A Cournot competitor takes into account the effect of the increase in output on its own profits only.
Therefore, Cournot competitors "overproduce" relative to the collusive (monopoly) point.
Further, this problem gets "worse" as the number of competitors grows because the market share of each individual firm falls, increasing the difference between the private gain from increasing production and the profit destruction effect on rivals.
Therefore, the more concentrated the industry in the Cournot case, the higher the price-cost margin.

41. Cournot, Bertrand, and Monopoly Equilibriums
Homogeneous product Bertrand resulted in zero profits, whereas the Cournot case resulted in positive profits. Why?
The best response functions in the Cournot model slope downward. In other words, the more aggressive a rival (in terms of output), the more passive the Cournot firm's response.
The best response functions in the Bertrand model slope upward. In other words, the more aggressive a rival (in terms of price) the more aggressive the Bertrand firm's response.

42. Cournot, Bertrand, and Monopoly Equilibriums
Cournot: Suppose firm j raises its output…the price at which firm i can sell output falls.
This means that the incentive to increase output falls as the output of the competitor rises.
Bertrand: Suppose firm j raises price the price at which firm i can sell output rises.
As long as firm's price is less than firm's, the incentive to increase price will depend on the (market) marginal revenue.

43. Kinked Demand Curve Model
Proposed by Paul Sweezy
If an oligopolist raises price, other firms will not follow, so demand will be elastic
If an oligopolist lowers price, other firms will follow, so demand will be inelastic
Implication is that demand curve will be kinked, MR will have a discontinuity, and oligopolists will not change price when marginal cost changes

44. Kinked Demand Curve Model
A model of oligopoly in which the demand curve facing each individual firm has a “kink” in it.
The kink results from the assumption that
1) competitor firms will follow if a single firm cuts price
2) but will not follow if a single firm raises price.
This model assumes that the elasticity of demand in response to an increase in price is different from the elasticity of demand in response to a price cut.

45. Sweezy’s kinked demand curve model of oligopoly
Assumptions:
If a firm raises prices, other firms won’t follow and the firm loses a lot of business.
So demand is very responsive or elastic to price increases.
2. If a firm lowers prices, other firms follow and the firm doesn’t gain much business.
So demand is fairly unresponsive or inelastic to price decreases.

46. THE KINKED DEMAND CURVE
Each firm believes that if it raises its price above the current price P*, none of its competitors will follow suit, so it will lose most of its sales.
Each firm also believes that if it lowers price, everyone will follow suit, and its sales will increase only to the extent that market demand increases.
As a result, the firm’s demand curve D is kinked at price P*, and its marginal revenue curve MR is discontinuous at that point.
If marginal cost increases from MC to MC’, the firm will still produce the same output level Q* and charge the same price P*.

47. Cartels Collusion 1) Centralized Cartel 2) Market-Sharing Cartel
Cooperation among firms to restrict competition in order to increase profits
1) Centralized Cartel
Formal agreement among member firms to set a monopoly price and restrict output
Incentive to cheat
2) Market-Sharing Cartel
Collusion to divide up markets