Analyse monopolistic competition
Explain product differentiation, entry, short-run supernormal profit and long-run normal profit.
Different Market Structures: Monopolistic Competition and Oligopoly
Real markets often lie between perfect competition and monopoly. This chapter explains how differentiated products, strategic interdependence, entry conditions and potential competition shape the behaviour and performance of firms.
Monopolistic competitionOligopolyGame theoryContestabilityConcentration ratios
What this chapter prepares you to do
Analyse oligopoly
Use strategic interdependence, non-price competition and game theory to explain firm behaviour.
Judge contestability
Assess whether the threat of hit-and-run entry can constrain incumbent firms.
Measure concentration
Calculate and interpret n-firm concentration ratios while recognising their limitations.
High-grade habit: do not identify a market structure from the number of firms alone. Link the number of firms to product differentiation, entry barriers, strategic interdependence and the firm's influence over price.
Chapter sections
19.1
Monopolistic competition
Monopolistic competition describes a market with many firms selling products that are close substitutes but are differentiated. Each firm therefore has a small degree of monopoly power over its own version of the product while still facing substantial competition.
Easy example: think of a city centre containing many restaurants, cafés and takeaway outlets. They compete for the same broad group of customers, but each tries to be slightly different through cuisine, location, atmosphere, service, branding or quality. That differentiation gives each firm some control over its own price while close substitutes keep competitive pressure strong.
Key characteristics
Downward-sloping demand
Because products are differentiated, a firm can alter its own price without losing every customer. Its demand curve is therefore downward sloping.
Product differentiation
Firms distinguish products through branding, design, quality, location, service or advertising. This can create brand loyalty and some price-setting power.
Low barriers to entry
New firms can usually enter when existing firms make supernormal profit. This entry is central to the long-run outcome.
Many firms
There are enough sellers that the action of one firm usually has little direct effect on any single rival.
No dominant firm
No firm is powerful enough to dictate how the whole market operates.
Close substitutes
Consumers can switch between rival differentiated products, so demand is typically more elastic than under monopoly.
Do not confuse differentiation with a completely different product. Rival products remain substitutes, but firms try to make consumers perceive meaningful differences between them.
Short-run equilibrium
A profit-maximising firm chooses output where MR = MC, then reads the corresponding price from its downward-sloping demand/AR curve. In the short run it may earn supernormal profit, normal profit or make a loss depending on the position of demand relative to costs.
Short-run equilibrium under monopolistic competition
The representative firm chooses qₛ where MR = MC and then charges pₛ from its downward-sloping demand curve. Because pₛ is above average cost at that output, the firm earns supernormal profit in the short run.
Adapted from Cambridge International AS & A Level Economics, Second Edition, by Peter Smith (with Adam Wilby and Mila Zasheva).
Entry and long-run adjustment
Supernormal profit attracts entrants because barriers are low. New differentiated products take some customers from existing firms, shifting each existing firm's demand curve to the left and often making it more elastic because consumers have more alternatives. Entry continues until the representative firm's demand curve is tangent to its average cost curve at the profit-maximising output.
Long-run equilibrium under monopolistic competition
Entry of new differentiated products reduces each incumbent firm’s demand until its AR curve is tangent to AC. The firm still chooses output where MR = MC, but AR = AC at that point, so only normal profit remains in long-run equilibrium.
Adapted from Cambridge International AS & A Level Economics, Second Edition, by Peter Smith (with Adam Wilby and Mila Zasheva).
Important comparison with perfect competition: the monopolistically competitive firm would like to sell more at the current price, but it faces a downward-sloping demand curve. In long-run equilibrium it has excess capacity, price exceeds marginal cost and output is below the minimum-average-cost level.
Efficiency and evaluation
Productive efficiency
Not achieved in long-run equilibrium because the firm produces to the left of minimum AC. It has excess capacity: output could be higher at a lower average cost.
Allocative efficiency
Not achieved because price exceeds marginal cost at the profit-maximising output.
Possible cost
Advertising and continual differentiation can raise average costs. Some resources may be used mainly to protect brand loyalty rather than lower production cost.
Possible benefit
Consumers gain variety and choice. Competitive pressure among many firms can also reduce the risk of X-inefficiency and encourage quality improvements.
19.2
Oligopoly
An oligopoly is a market dominated by a few firms. Its defining feature is strategic interdependence: when one firm changes price, output, advertising or product design, rivals may respond, so each firm must consider likely reactions before acting.
Core characteristics
Few dominant firms
A small number of sellers account for a large share of market output.
Strategic interdependence
One firm's decisions can materially change rivals' sales and profits, so behaviour is strategic.
Barriers to entry
Economies of scale, brand loyalty, technology, high capital requirements or strategic behaviour can make entry difficult.
Oligopoly often emerges where economies of scale are significant enough that only a limited number of firms can operate efficiently, but not so extensive that the market becomes a natural monopoly.
Competition versus cooperation
Oligopolists may compete aggressively or cooperate. Strong rivalry can move the outcome closer to the competitive end of the market-structure spectrum. Cooperation or collusion can move it towards the monopoly end by allowing firms to restrict output and raise joint profits.
Non-price competition
Non-price competition occurs when firms compete without directly cutting the headline price. Common methods include advertising, branding, design, quality improvements, loyalty schemes, packaging, customer service and product innovation.
Why firms may prefer it
A price cut can trigger retaliation and a price war. Non-price methods may win customers while preserving the market price.
Possible consumer effects
Consumers may gain better quality, innovation and choice, although intensive advertising and differentiation can increase firms' costs.
Game theory
Game theory models situations where each firm's payoff depends on both its own choice and the choices of rivals. It is especially useful in oligopoly because firms are interdependent.
Two-firm pay-off matrix
Suppose two firms can choose a high or low price. Each cell shows the profit of Firm A first and Firm B second, in millions.
| Firm A \ Firm B | High price | Low price |
|---|---|---|
| High price | A: 8 · B: 8 | A: 1 · B: 12 |
| Low price | A: 12 · B: 1 | A: 4 · B: 4 |
For Firm A, low price gives the higher profit whether B chooses high or low. The same is true for Firm B. Both therefore choose low, producing 4 + 4 = 8 total profit even though joint profit would have been 16 if both had chosen high.
Prisoners' Dilemma, dominant strategy and Nash equilibrium
Prisoners' Dilemma
A strategic problem in which individually rational choices can produce a worse joint outcome than cooperation would have produced.
Dominant strategy
A strategy that gives a player the best payoff regardless of what the other player chooses.
Nash equilibrium
A combination of strategies in which each player's choice is best given the other player's choice, so neither has an incentive to change unilaterally.
Matrix technique: evaluate each firm's best response to every possible rival choice. Do not simply choose the cell with the highest combined profit unless the question asks for joint-profit maximisation.
Advantages and disadvantages of oligopoly
| Possible benefits when rivalry is strong | Possible problems when firms cooperate or competition is weak |
|---|---|
| Competitive prices and pressure to control costs | Higher prices and restricted output |
| Innovation, product development and non-price competition | Collusion can create monopoly-like welfare losses |
| Potential economies of scale | Barriers to entry can protect long-run supernormal profit |
| Choice between differentiated products | Possible X-inefficiency when rivalry is weak |
Extension: monopsony
A monopsony is a market with a single buyer. A powerful buyer may be able to influence the price and conditions offered to suppliers. The idea is particularly important in some input and labour markets.
19.3
Contestable markets
The theory of contestable markets focuses on potential competition. Even a market with only one incumbent firm may behave competitively if entry and exit are sufficiently easy for credible rivals to enter whenever supernormal profit appears.
Conditions for strong contestability
No entry or exit barriers
Potential entrants must be able to enter and leave rapidly without being blocked by legal, structural or strategic obstacles.
No sunk costs
Costs incurred on entry must be recoverable on exit. Otherwise a short-lived entry attempt could be too risky.
No incumbent cost advantage
Entrants must be able to operate with comparable costs rather than facing a built-in disadvantage.
Equal access to technology
Potential entrants need access to the same or equivalent production technology.
Hit-and-run entry
Hit-and-run entry means entering to capture short-run supernormal profit and then leaving again if conditions deteriorate. The threat of such entry can persuade an incumbent to keep price close to average cost and avoid obvious X-inefficiency.
Book-style example: a domestic airline route can be relatively contestable if another airline already owns a spare aircraft. The potential entrant may be able to place that aircraft on the route, take some short-run profit and leave again without having to recover a large route-specific investment. The example works only to the extent that sunk costs and other entry barriers are genuinely low.
Incumbent raises P above AC
→Supernormal profit appears
→Potential entrant is attracted
→Entry threat constrains price
Contestability
If an incumbent charges a price that creates supernormal profit, a potential entrant may enter briefly and take some of that profit. The threat of such hit-and-run entry can force the incumbent to keep price closer to average cost, provided entry and exit are genuinely easy and sunk costs are negligible.
Adapted from Cambridge International AS & A Level Economics, Second Edition, by Peter Smith (with Adam Wilby and Mila Zasheva).
Does contestability guarantee efficiency?
No. The threat of entry can reduce supernormal profit and managerial slack, but a firm charging price equal to average cost need not be at minimum average cost, and price need not equal marginal cost. Productive and allocative efficiency therefore are not automatically achieved.
Internet and contestability
Online search, price comparison and digital selling can lower information and entry costs in some markets. This can make it easier for new firms to reach customers and increase competitive pressure on incumbents. The effect depends on whether significant sunk costs, network advantages, regulation or other barriers remain.
19.4
Market concentration
Market concentration describes how much of a market is accounted for by the largest firms. A common measure is the n-firm concentration ratio: the combined market share of the largest n firms.
n-firm concentration ratio
= market share of largest firm + second-largest + … + nth-largest firm
= market share of largest firm + second-largest + … + nth-largest firm
Worked example
Suppose the largest five firms have market shares of 31%, 24%, 15%, 9% and 7%.
3-firm concentration ratio = 31 + 24 + 15 = 70%
5-firm concentration ratio = 31 + 24 + 15 + 9 + 7 = 86%
This indicates substantial concentration, but the ratio alone does not tell us how strongly the largest firm dominates or how aggressively the firms compete.
Interpreting concentration carefully
Market definition matters
A concentration figure can change sharply depending on whether the market is defined narrowly or broadly by product, geography or customer group.
Same ratio, different dominance
A 75% five-firm ratio could mean one firm has 60% and four firms share 15%, or five firms each have 15%. Strategic behaviour would likely differ.
Output is usually more useful than employment
Employment shares can differ from sales/output shares when large firms use more capital-intensive production.
Concentration is not behaviour
A highly concentrated market may still be strongly competitive if firms rival each other or the market is contestable.
Market dominance
A market can be concentrated without one firm being individually dominant. Market dominance refers to a firm holding enough market power to influence market conditions to a significant degree. When interpreting concentration data, examine the leading firm's share as well as the combined share of the largest firms, and then consider entry barriers and the behaviour of rivals.
Minimum efficient scale and concentration
The size of minimum efficient scale (MES) relative to total market demand helps determine how many efficient firms the market can support. If MES is small, many firms can coexist. If MES is large, only a few firms can reach low average cost; if scale economies extend across almost the whole market, a natural monopoly may result.
How many firms can a market support?
The diagram shows the minimum efficient scale (MES) at Qmes. When MES is large relative to total market demand, only a small number of firms may be able to operate at low average cost, increasing market concentration.
Adapted from Cambridge International AS & A Level Economics, Second Edition, by Peter Smith (with Adam Wilby and Mila Zasheva).
Evaluation chain: concentration ratio → size distribution among leading firms → entry barriers/contestability → actual rivalry or cooperation → likely price, output, innovation and efficiency. A concentration ratio is evidence about structure, not proof of anti-competitive behaviour.
Chapter 19 revision checklist
Define monopolistic competition.
Explain product differentiation and brand loyalty.
State the main characteristics of monopolistic competition.
Explain short-run equilibrium and possible supernormal profit.
Explain how entry changes the firm's demand curve.
Explain long-run tangency and normal profit.
Evaluate productive and allocative efficiency under monopolistic competition.
Explain benefits and costs of product variety and advertising.
Define oligopoly and strategic interdependence.
Explain why economies of scale can contribute to oligopoly.
Explain non-price competition with examples.
Distinguish rivalry from cooperation/collusion.
Use a two-player pay-off matrix.
Explain the Prisoners' Dilemma.
Define dominant strategy and Nash equilibrium.
Define contestable market and hit-and-run entry.
State the conditions needed for strong contestability.
Evaluate efficiency in a contestable market.
Calculate and interpret an n-firm concentration ratio.
Explain how MES, market definition and firm-size distribution affect concentration analysis.
20 questions. Each answer is marked immediately with a short explanation of why it is correct or incorrect.