Unit 6: Market Failure and the Role of Government

Market failure

When an unregulated market outcome does not achieve allocative efficiency (does not maximize society’s total net benefit), so the market quantity differs from the socially efficient quantity.

Allocative efficiency

A condition where the quantity produced and consumed maximizes total net benefit; occurs at the quantity where marginal benefit equals marginal cost.

Social efficiency

Efficient resource allocation when society’s marginal social benefit from the last unit equals its marginal social cost (MSB = MSC).

Marginal benefit (MB)

The additional benefit to consumers/society from consuming one more unit of a good.

Marginal cost (MC)

The additional cost to producers/society of producing one more unit of a good.

Marginal social benefit (MSB)

The total marginal benefit to society from one more unit, including spillover (external) benefits.

Marginal social cost (MSC)

The total marginal cost to society of one more unit, including spillover (external) costs.

Perfectly competitive market equilibrium condition

In a competitive market with no spillovers and good information, equilibrium occurs where supply equals demand, corresponding to MB = MC.

Perfectly competitive firm output rule

A price-taking firm produces where price equals marginal cost (P = MC).

Perfectly competitive labor market condition

The wage equals the marginal revenue product of labor (W = MRP).

Total surplus

The sum of consumer surplus and producer surplus; maximized at the socially efficient quantity.

Consumer surplus (CS)

The difference between what consumers are willing to pay and what they actually pay.

Producer surplus (PS)

The difference between the price producers receive and the minimum they would accept; represented by the area above the marginal cost curve and below price.

Deadweight loss (DWL)

Net benefits (gains from trade) that are lost when the market quantity is not the efficient quantity.

Market power

The ability of a firm (or firms) to influence price by restricting output; a cause of market failure because output is too low and price too high versus competitive efficiency.

Asymmetric (imperfect) information

A situation where one side of a transaction has more or better information than the other, potentially reducing efficiency.

Externality

A cost or benefit from production or consumption that affects third parties not involved in the transaction, causing MSB ≠ MSC.

Negative externality

An externality that imposes costs on third parties (e.g., pollution), typically leading to overproduction relative to the social optimum.

Positive externality

An externality that creates benefits for third parties (e.g., vaccinations, education), typically leading to underconsumption/underproduction relative to the social optimum.

Marginal private cost (MPC)

The marginal cost borne by the producer/decision-maker, excluding external costs; often represented by the market supply curve in externality problems.

Marginal external cost (MEC)

The additional spillover cost imposed on third parties from producing/consuming one more unit.

Negative externality cost relationship

In a negative production externality, marginal social cost equals marginal private cost plus marginal external cost (MSC = MPC + MEC).

Marginal private benefit (MPB)

The marginal benefit received by the consumer/decision-maker, excluding external benefits; often represented by the market demand curve.

Marginal external benefit (MEB)

The additional spillover benefit received by third parties from producing/consuming one more unit.

Positive externality benefit relationship

In a positive consumption externality, marginal social benefit equals marginal private benefit plus marginal external benefit (MSB = MPB + MEB).

Private (market) equilibrium in an externality model

The outcome where MPB intersects MPC (buyers and sellers account only for private benefits and private costs).

Socially efficient outcome in an externality model

The outcome where MSB intersects MSC (includes spillover benefits and spillover costs).

Overproduction (externality context)

A situation typical of negative externalities where the market produces more than the socially efficient quantity because MSC > MPC.

Underproduction (externality context)

A situation typical of positive externalities where the market produces/consumes less than the socially efficient quantity because MSB > MPB.

Internalizing the externality

Adjusting private incentives so decision-makers face the full social cost or receive the full social benefit, moving the outcome toward MSB = MSC.

Pigouvian (corrective) tax

A per-unit tax designed to reduce negative externalities by raising private marginal cost; ideally set equal to MEC at the efficient quantity.

Corrective subsidy

A per-unit subsidy designed to increase consumption/production when there is a positive externality; ideally set equal to MEB at the efficient quantity.

Regulation (command-and-control)

Rules that require or prohibit certain actions (e.g., emissions limits) to reduce external harms; effectiveness depends on monitoring/enforcement and relative abatement costs.

Abatement cost

The cost of reducing an external harm (e.g., the cost of cutting pollution).

Tradable permits (cap-and-trade)

A policy where the government sets a total cap on emissions and issues permits that can be bought and sold, achieving a targeted quantity of pollution at lower total cost.

Coase Theorem

If property rights are clearly defined and transaction costs are low, private bargaining can reach an efficient outcome regardless of initial assignment of rights.

Transaction costs

Costs of making and enforcing agreements (e.g., bargaining, legal, monitoring costs) that can prevent Coasian bargaining from achieving efficiency.

Rivalrous good

A good where one person’s consumption reduces the amount available for others (e.g., food, shoes).

Nonrivalrous good

A good where one person’s consumption does not reduce availability for others (e.g., national defense).

Excludable good

A good where non-payers can be prevented from consuming/enjoying benefits.

Nonexcludable good

A good where it is difficult or impossible to prevent non-payers from accessing benefits (e.g., clean air).

Public good

A good that is both nonexcludable and nonrival; tends to be underprovided by private markets.

Free-rider problem

When individuals have an incentive to enjoy the benefits of a nonexcludable good without paying, leading to underprovision in private markets.

Efficient provision rule for a public good

Determine MSB by vertically summing individuals’ marginal benefits (e.g., MSB = MB1 + MB2) and set MSB = MC to find the efficient quantity.

Common resource (common-pool resource)

A good/resource that is nonexcludable but rival (e.g., fisheries, congested roads); tends to be overused.

Tragedy of the commons

Overuse/depletion of a common resource because individuals gain private benefits while sharing congestion/depletion costs with others.

Adverse selection

An asymmetric information problem where hidden characteristics (before the transaction) lead to too many low-quality products or high-risk participants in the market.

Moral hazard

An asymmetric information problem where hidden actions (after the transaction) cause one party to take riskier behavior because they don’t bear full consequences.

Signaling

Actions taken to reveal information and reduce asymmetric information (e.g., warranties, degrees, certifications).

Screening

Methods used to induce others to reveal information or sort themselves into groups (e.g., deductibles, different insurance coverage tiers).