2.7 The Effects of Government Interventions in Markets

Price Ceilings and Floors

A price ceiling is a legal maximum price set below equilibrium, causing a shortage (Qd > Qs) — e.g., rent control. A price floor is a legal minimum price set above equilibrium, causing a surplus (Qs > Qd) — e.g., minimum wage. Ceilings/floors set at or beyond equilibrium have no effect on the market.

Taxes and Subsidies Shift Curves

A tax on producers shifts supply left (reduces quantity, raises price paid by consumers, lowers price received by sellers), creating a tax wedge and deadweight loss. A subsidy shifts supply right, lowering consumer price and raising producer revenue, increasing quantity beyond equilibrium and also causing deadweight loss from overproduction.

Measuring Welfare Effects

Interventions change consumer surplus (CS) and producer surplus (PS). Any quantity restriction away from equilibrium (ceiling, floor, tax) creates deadweight loss (DWL) — a loss of total surplus with no offsetting gain, representing missed mutually beneficial trades. Government revenue from a tax equals tax per unit × quantity sold.

Key terms

Price ceiling

A legal maximum price; if set below equilibrium, it causes a shortage.

Price floor

A legal minimum price; if set above equilibrium, it causes a surplus.

Tax wedge

The gap between the price buyers pay and the price sellers receive, created by a per-unit tax.

Deadweight loss

The loss of total surplus (CS + PS) from trades that don't occur due to market interventions like taxes, ceilings, or floors.

Subsidy

A payment from the government to producers that shifts supply right, lowering consumer price and increasing quantity, but potentially causing overproduction and deadweight loss.

Try an AP-style question

What results?

1. A surplus of apartments
2. Higher rents
3. A shortage of apartments
4. No effect on the market