Market Failure and Externalities
Market Failure &
Externalities.
Private decisions can impose costs or create benefits beyond the buyer and seller. Learn why market equilibrium may diverge from social efficiency—and how policy can respond.
Observe
Look beyond the transaction.
Some consequences fall on
people outside the market.
A factory and its customers consider production costs and product benefits, but nearby residents may bear pollution-related health costs. Conversely, vaccination and education can create benefits for people who do not purchase them directly.
THE MISSING QUESTION
Who else is affected by this decision—and is that effect included in the price?
Think
Add private and external effects.
Social value includes
the spillover.
With a negative production externality, marginal social cost exceeds marginal private cost. The unregulated market therefore produces more than the socially efficient quantity. A positive externality reverses the problem: the market tends to provide too little.
External cost
MSC = MPC + marginal external cost. Market output is excessive.
External benefit
MSB = MPB + marginal external benefit. Market output is insufficient.
MSC = MPC + MEC · MSB = MPB + MEBSocial efficiency occurs where marginal social benefit equals marginal social cost.
Analyse
Internalise the spillover.
Set a corrective tax
equal to marginal damage.
Increase the external cost per unit. The social-cost curve moves upward, the efficient quantity falls, and the appropriate Pigouvian tax rises.
Pollution-policy laboratory
INTERACTIVE EXTERNALITY
External damage
MARKET QUANTITY50EFFICIENT QUANTITY40CORRECTIVE TAX€20EXCESS OUTPUT10
The tax aligns the producer’s private cost with the social cost imposed by production.
Apply
Compare policy instruments.
Correcting failure requires
information and institutional judgement.
No instrument is automatically best. Taxes use price signals, tradable permits cap aggregate quantity, and regulation mandates behaviour or technology. Policy design must consider measurement, enforcement, distribution and administrative capacity.
Corrective tax
Charges each unit according to estimated marginal external damage.
Tradable permits
Caps total emissions while allowing exchange of pollution rights.
Regulation
Sets limits or technical standards when direct control is preferred.
Decide
Choose the correct margin.
What tax restores
social efficiency?
At the socially efficient quantity, a factory’s marginal private cost is €45 and its marginal external pollution cost is €15. Marginal benefit is €60.
MODULE 08 · CHECKPOINT
You can now see
beyond the market price.
Externalities separate private incentives from social value. Effective policy brings external costs or benefits into the decision-making margin.
