16.9
Quantity-based interventions aim to address externalities by directly controlling the amount of a good or activity.
Quotas are a prime example of this approach. They set a clear limit on how much of a certain good can be produced or consumed.
For instance, fishing quotas limit the number of fish caught. This is done to prevent overfishing, ensuring the long-term sustainability of fish populations.
Without a quota, fishermen would catch fish up to where their private marginal cost intersects with market demand.
To set the quota, the external marginal cost is added to the private marginal cost to form the social marginal cost curve. The intersection of this curve with the market demand curve shows the socially optimal quantity and price of fish. This quantity determines the size of the quota. Once the quota is imposed, the market supply curve becomes vertical at this quantity, ensuring sustainable fishing levels.
Other examples of quotas include emissions restrictions for factories and noise restrictions for residential areas.
Quotas can also be used to encourage positive externalities, like mandating school attendance until a certain age, compulsory vaccinations, or the purchase of auto liability insurance.
Private market interactions often fail to account for externalities, which are unintended costs or benefits experienced by third parties, resulting in…
Copyright © 2026 MyJoVE Corporation. All rights reserved.