Revise Efficiency and market failure for Cambridge 9708 (7.3)

Productive efficiency is achieved when goods and services are produced using the minimum possible amount of scarce resources, resulting in the lowest possible cost per unit. This occurs at the lowest point on a firm's average cost (AC) curve, where average cost equals marginal cost (AC=MC). From a macroeconomic perspective, an economy is productively efficient when it operates on its Production Possibility Curve (PPC), meaning it is impossible to produce more of one good without producing less of another. It signifies that resources are not being wasted through unemployment or underemployment. While crucial, productive efficiency alone does not guarantee an optimal outcome for society, as the goods being produced might not be the ones consumers actually want.

Allocative efficiency, also known as Pareto efficiency, is a state where resources are allocated to produce the combination of goods and services that consumers most value. This optimal distribution occurs when the price (P) consumers are willing to pay for a good is equal to the marginal cost (MC) of producing it. The price reflects the marginal private benefit (or utility) to the consumer, while the marginal cost represents the opportunity cost of the resources used. When P=MC, it means the value society places on the last unit produced is exactly equal to the cost of the resources needed to make it. Any deviation from this point implies a misallocation of resources and a loss of social welfare.

Market failure occurs when the free market, operating without any government intervention, fails to allocate resources efficiently, leading to a net loss of social welfare. This happens when the conditions for productive and/or allocative efficiency are not met. The main causes of market failure include the existence of externalities (where P ≠ MSC/MSB), the provision of public goods (which are non-excludable and non-rival), information gaps, and the abuse of monopoly power. In each case, the market mechanism of supply and demand fails to produce the socially optimal quantity of a good or service. For example, a firm producing negative externalities will overproduce because it ignores the external costs, leading to P < MSC and thus allocative inefficiency.

Deadweight loss (or welfare loss) is the quantifiable measure of the loss of economic efficiency that occurs when a market is not in a state of competitive equilibrium. It represents the combined loss of consumer and producer surplus that is not transferred to any other party, such as the government. Graphically, it is shown by a triangle that points towards the socially optimal equilibrium point, with its area representing the value of the welfare lost. Deadweight loss arises from market failures like monopoly power (where output is restricted and price is raised) or externalities (where social costs/benefits are ignored), as well as from government interventions like taxes, subsidies, or price controls. It visualises the cost to society of not achieving allocative efficiency.

Productive efficiency — producing at the lowest average cost (minimum ATC). On a PPF, this means operating on the frontier.

Allocative efficiency — producing the right quantity for society where MSB = MSC. This maximises total welfare.

A market can be productively efficient but allocatively inefficient (e.g. monopoly at minimum ATC but P > MC).

When the market produces at Q_market ≠ Q_social, welfare is lost. Shade the DWL triangle between MSC and MSB from Q_social to Q_market.

• Overproduction (negative externality): Q_market > Q_social → DWL to the right of Q_social.
• Underproduction (positive externality): Q_market < Q_social → DWL to the right of Q_market.