4.1 Introduction to Market Structures

Market structure describes the competitive environment in which firms operate. The number of sellers, the nature of products, entry barriers, and the degree of control over prices determine how firms make production and pricing decisions.

 4.1.1 Main Types of Market Structures

The four principal models covered in this unit are perfect competition, monopoly, monopolistic competition, and oligopoly.

 4.1.1.1 Key Differences

Perfect competition has many sellers and homogeneous products; monopoly has a single dominant seller; monopolistic competition involves differentiated products and many firms; and oligopoly is characterized by a small number of strategically interdependent firms.

 4.2 Perfect Competition

Perfect competition is a theoretical market structure in which numerous buyers and sellers trade identical products, and individual firms cannot influence the prevailing market price.

 4.2.1 Basic Features

– A large number of buyers and sellers.
– Homogeneous products.
– Freedom of entry and exit in the standard model.
– Sufficient information about prices and products.
– Individual firms act as price takers.

 4.2.1.1 Short-Run Firm Equilibrium

A competitive firm maximizes profit by producing where marginal cost equals marginal revenue, provided the relevant second-order and operating conditions are satisfied.

$$
P=AR=MR
$$

For a profit-maximizing competitive firm, the usual output condition is $MC=MR=P$, with marginal cost rising through marginal revenue at the optimum.

 4.2.2 Short-Run Profit and Shutdown Decisions

A firm may earn an economic profit, break even, or incur a loss depending on the relationship between market price and average total cost.

 4.2.2.1 Shutdown Condition

In the standard short-run model, a firm should temporarily shut down if the price falls below the minimum average variable cost. If the price covers the average variable cost but not the average total cost, the firm may continue operating to contribute towards fixed costs.

 4.2.3 Long-Run Equilibrium

In the long run, entry and exit tend to eliminate economic profits and losses in the standard competitive model.

 4.2.3.1 Economic Efficiency

Long-run equilibrium under standard assumptions occurs where price equals marginal cost and minimum long-run average cost. This supports allocative and productive efficiency.

 4.3 Monopoly

A monopoly is a market structure in which a single firm supplies a product or service with no close substitutes and entry barriers protect it from direct competition.

 4.3.1 Main Characteristics

A monopolist faces the market demand curve, has some control over price, and may benefit from barriers such as patents, exclusive resource access, legal restrictions, or substantial economies of scale.

 4.3.1.1 Short-Run Monopoly Equilibrium

A profit-maximizing monopolist generally selects output where marginal revenue equals marginal cost. It then determines the price consumers are willing to pay for that quantity from the demand curve.

Unlike a competitive firm, a monopolist generally faces a downward-sloping demand curve and has marginal revenue below price.

 4.3.2 Long-Run Monopoly Equilibrium

Barriers to entry can allow a monopolist to maintain positive economic profits in the long run. However, profit is not guaranteed: demand may be weak or costs may be high enough to generate losses.

 4.3.2.1 Welfare Cost of Monopoly

Compared with the competitive benchmark under standard assumptions, monopoly typically restricts output and charges a higher price. The resulting reduction in mutually beneficial transactions can create deadweight loss.

 4.3.3 Price Discrimination

Price discrimination occurs when a seller charges different prices for the same or closely equivalent product to different buyers, and the price differences are not fully explained by differences in production costs.

 4.3.3.1 Three Degrees of Price Discrimination

– First degree: The seller charges each buyer their maximum willingness to pay, in the idealized case.
– Second degree: Prices vary according to quantity purchased or product version, such as bulk discounts.
– Third degree: Different identifiable consumer groups face different prices, such as eligible student discounts.

Price discrimination generally requires some degree of market power and an ability to limit resale between customer groups.

 4.4 Monopolistic Competition

Monopolistic competition is a market structure with many firms selling products that are similar but differentiated by quality, design, location, branding, or customer experience.

 4.4.1 Basic Characteristics

The market contains many sellers, differentiated products, relatively accessible entry and exit, and limited individual control over price.

 4.4.1.1 Demand and Cost Conditions

A firm faces a downward-sloping demand curve because consumers may prefer its product over alternatives. Its cost structure depends on production conditions, and its profit-maximizing output is determined by the relationship between marginal revenue and marginal cost.

 4.4.2 Short-Run Equilibrium

In the short run, a monopolistically competitive firm may earn economic profits, break even, or incur losses.

 4.4.2.1 Profit-Maximising Output

The firm selects output where marginal revenue equals marginal cost, then uses its demand curve to determine the corresponding price.

 4.4.3 Long-Run Equilibrium and Excess Capacity

Entry and exit tend to eliminate economic profits in the long run under the standard model. However, product differentiation allows firms to retain some market power.

 4.4.3.1 Meaning of Excess Capacity

Excess capacity occurs when a firm produces below the output level associated with minimum average cost. The firm may operate with unused potential production capacity because its downward-sloping demand curve does not support the output required for minimum average cost at the prevailing price.

 4.5 Oligopoly

An oligopoly is a market structure dominated by a small number of large firms. Each firm’s decisions can influence the profits and strategic responses of its competitors.

 4.5.1 Features of Oligopoly

– A small number of major sellers.
– Strategic interdependence among firms.
– Barriers that make market entry difficult.
– Products that may be homogeneous or differentiated.
– The possibility of price competition, non-price competition, or coordination.

 4.5.1.1 Strategic Interdependence

An oligopolistic firm must consider how competitors may react to changes in its prices, output, advertising, and product strategy. As a result, decisions depend not only on demand and cost conditions but also on expectations about rival behavior.

 4.5.2 Kinked Demand Curve Model

The kinked demand curve theory explains why oligopolistic firms are often reluctant to change their prices. rigidity in certain oligopolistic markets.

 4.5.2.1 Price Rigidity

The model assumes that competitors may not follow a price increase but may match a price reduction. A firm that raises its price can lose customers, whereas a price cut may trigger similar cuts by rivals.

This asymmetry creates a kink in the firm’s perceived demand curve and a discontinuity in marginal revenue. Under the model’s assumptions, this can help explain why prices remain stable despite moderate cost changes.

 4.5.3 Dominant Price Leadership Model

Price leadership occurs when one firm establishes a price that other firms in the industry follow. In a dominant-firm model, the leading firm has a substantial market position and may account for a large share of industry supply.

 4.5.3.1 Role of the Dominant Firm

The dominant firm considers market demand and the supply offered by smaller firms when choosing its price and output. Other firms may accept the established price and determine their own output based on their costs.

Price leadership should be distinguished from explicit collusion: firms may follow a leader’s price without having a formal agreement.

 Final Revision: Essential Microeconomics Formulas

Demand, Supply, and Elasticity

 Elasticity Formulas

$$
PED=\frac{\%\Delta Q_d}{\%\Delta P}
$$

$$
YED=\frac{\%\Delta Q_d}{\%\Delta Y}
$$

$$
XED=\frac{\%\Delta Q_A}{\%\Delta P_B}
$$

$$
ES=\frac{\%\Delta Q_s}{\%\Delta P}
$$

Consumer Behavior

 Utility and Consumer Equilibrium

$$
MU=\frac{\ Delta TU}{\ Delta Q}
$$

$$
\frac{MU_X}{P_X}=\frac{MU_Y}{P_Y}
$$

$$
P_X X+P_Y Y=I
$$

$$
MRS_{XY}=\frac{P_X}{P_Y}
$$

Producer Behavior

 Production and Cost Formulas

$$
MP=\frac{\Delta TP}{\Delta L}
$$

$$
AP=\frac{TP}{L}
$$

$$
TC=TFC+TVC
$$

$$
AC=\frac{TC}{Q}
$$

$$
MC=\frac{\Delta TC}{\ Delta Q}
$$

 Optimal Input Combination

$$
MRTS_{LK}=\frac{P_L}{P_K}
$$

$$
\frac{MP_L}{P_L}=\frac{MP_K}{P_K}
$$

 Market Structures

Competitive and Profit-Maximizing Output

$$
MR=MC
$$

Under perfect competition:

$$
P=AR=MR=MC
$$

For a monopolist, output is generally chosen where $MR=MC$, while price is determined by the demand curve.

The model assumes that competitors may not follow a price increase but may match a price reduction. A firm that raises its price can lose customers, whereas a price cut may trigger similar cuts by rivals.

This asymmetry creates a kink in the firm’s perceived demand curve and a discontinuity in marginal revenue. Under the model’s assumptions, this can help explain why prices remain stable despite moderate cost changes.

 4.5.3 Dominant Price Leadership Model

Price leadership occurs when one firm establishes a price that other firms in the industry follow. In a dominant-firm model, the leading firm has a substantial market position and may account for a large share of industry supply.

 4.5.3.1 Role of the Dominant Firm

The dominant firm considers market demand and the supply offered by smaller firms when choosing its price and output. Other firms may accept the established price and determine their own output based on their costs.

Price leadership should be distinguished from explicit collusion: firms may follow a leader’s price without having a formal agreement.

 Final Revision: Essential Microeconomics Formulas

 Demand, Supply and Elasticity

 Elasticity Formulas

$$
PED=\frac{\%\Delta Q_d}{\%\Delta P}
$$

$$
YED=\frac{\%\Delta Q_d}{\%\Delta Y}
$$

$$
XED=\frac{\%\Delta Q_A}{\%\Delta P_B}
$$

$$
ES=\frac{\%\Delta Q_s}{\%\Delta P}
$$

 Consumer Behaviour

 Utility and Consumer Equilibrium

$$
MU=\frac{\Delta TU}{\Delta Q}
$$

$$
\frac{MU_X}{P_X}=\frac{MU_Y}{P_Y}
$$

$$
P_X X+P_Y Y=I
$$

$$
MRS_{XY}=\frac{P_X}{P_Y}
$$

 Producer Behaviour

 Production and Cost Formulas

$$
MP=\frac{\Delta TP}{\Delta L}
$$

$$
AP=\frac{TP}{L}
$$

$$
TC=TFC+TVC
$$

$$
AC=\frac{TC}{Q}
$$

$$
MC=\frac{\Delta TC}{\Delta Q}
$$

 Optimal Input Combination

$$
MRTS_{LK}=\frac{P_L}{P_K}
$$

$$
\frac{MP_L}{P_L}=\frac{MP_K}{P_K}
$$

 Market Structures

 Competitive and Profit-Maximising Output

$$
MR=MC
$$

Under perfect competition:

$$
P=AR=MR=MC
$$

For a monopolist, output is generally chosen where $MR=MC$, while price is determined by the demand curve.