Monopolistic Competition and Oligopoly: Market Structures and Strategic Behavior

Chapter 15: Monopolistic Competition

Definition and Characteristics

Monopolistic competition is a market structure characterized by many firms, differentiated products, and free entry and exit. This structure is common in industries where firms offer similar but not identical products.

• Product Differentiation: Each firm offers a product that is slightly different from its competitors, allowing for some degree of market power.

• Examples: Restaurants, clothing brands, coffee shops, and many retail products.

Demand and Revenue

• A monopolistically competitive firm faces a downward-sloping demand curve due to product differentiation.

• Demand equals average revenue (AR) for the firm.

• Marginal revenue (MR) lies below the demand curve because the firm must lower its price to sell additional units.

Short-Run Decisions and Profit

• In the short run, the firm chooses output where marginal revenue equals marginal cost (MR = MC).

• After determining output, the firm charges the price indicated by the demand curve for that quantity.

• Possible outcomes in the short run:

  • Economic profit

  • Zero economic profit

  • Economic loss

Equation:

$MR = MC$

Long-Run Equilibrium

• Free entry and exit ensure that economic profit is driven to zero in the long run.

• If firms earn positive economic profit, new firms enter, decreasing each existing firm's demand.

• If firms incur losses, some exit, increasing demand for remaining firms.

• Long-run equilibrium occurs where price equals average total cost (P = ATC).

• Firms typically produce below the minimum point of average total cost, resulting in excess capacity.

Equation:

$P = ATC$

Efficiency and Welfare

• Monopolistic competition is not perfectly efficient because price exceeds marginal cost (P > MC).

• However, it provides benefits through product variety and consumer choice.

Advertising

• Firms use advertising to differentiate products, shift demand, or make demand less elastic.

Key Terms Table

Term	Definition
Monopolistic Competition	Market structure with many firms, differentiated products, and free entry/exit
Product Differentiation	Firms sell similar but not identical products
Excess Capacity	Difference between efficient scale and actual output in long-run equilibrium

Chapter 16: Oligopoly and Game Theory

Definition and Characteristics

Oligopoly is a market structure with a small number of firms that recognize their mutual interdependence. Each firm's decisions affect and are affected by the actions of other firms.

• Strategic Interdependence: Each firm's best decision depends on expectations about rivals' actions.

Game Theory Basics

• Game Theory: The study of strategic situations where each player's payoff depends on the actions of others.

• A game includes:

  • Players

  • Actions or strategies

  • Payoffs

• Strategy: A complete plan of action for a player.

• Payoff: The reward or outcome from a combination of strategies.

Game Representations

• Payoff Matrix: Table showing payoffs for different strategy combinations (normal form).

• Extensive Form: Game tree, often used for sequential games.

Types of Games

• Simultaneous Game: Players choose actions at the same time or without knowing others' choices.

• Sequential Game: One player moves first; the other observes before choosing.

• One-Shot Game: Played once.

• Repeated Game: Played multiple times.

Key Concepts in Game Theory

• Dominant Strategy: A strategy that yields a higher payoff regardless of the other player's choice.

• Nash Equilibrium: A set of strategies where no player can benefit by unilaterally changing their strategy, given the strategies of others.

• Nash equilibrium is defined in terms of strategies, not just outcomes or payoffs.

Prisoner's Dilemma

• A game where individual incentives lead to a non-cooperative outcome, even though mutual cooperation would be better for both players.

• Each player has an incentive to defect.

• The Nash equilibrium is typically inefficient compared to cooperation.

• Repeated interaction can sustain cooperation through the threat of future punishment.

Oligopoly Behavior and Models

• Cartel: An agreement among firms to coordinate price or output to increase joint profits (behaving like a monopoly).

• Cartels are often unstable due to incentives to cheat.

• Cartel stability is more likely with few firms, easy detection of cheating, repeated interaction, and credible punishment.

Oligopoly Models

Model	Firms Compete By	Key Feature
Cournot	Choosing quantities	Simultaneous quantity competition
Bertrand	Choosing prices	Simultaneous price competition
Stackelberg	One firm moves first	Sequential quantity competition

Market Outcomes

• Compared to perfect competition, oligopoly leads to higher prices and lower output.

• Compared to monopoly, oligopoly leads to lower prices and higher output when firms compete rather than collude.

• Entry by new firms increases competition in oligopoly markets.

Example: Payoff Matrix for a Prisoner's Dilemma

	Firm B: Cooperate	Firm B: Defect
Firm A: Cooperate	Both earn high profit	A earns low, B earns high
Firm A: Defect	A earns high, B earns low	Both earn low profit

Additional info: In oligopoly, firms must consider rivals' likely responses when making decisions. Game theory provides tools to analyze these strategic interactions, including the identification of Nash equilibria and the conditions under which cooperation can be sustained.