Topic 2.8 Notes – The Effects of Government Intervention in Markets

1. Price Controls in Competitive Markets

In a competitive market, equilibrium occurs where quantity demanded equals quantity supplied. That point maximizes total surplus (consumer surplus + producer surplus).

A price control is a legal maximum or minimum price set by the government.

Types of Price Controls

A control is binding only if it actually prevents the market from reaching equilibrium. Always check that first on MCQs.

2. Surplus, Shortages, and Deadweight Loss from Price Controls

Price Ceiling Effects

When price is forced below equilibrium:

• Qd increases, Qs decreases
• Shortage = Qd − Qs
• Some consumers gain from lower price
• Some consumers lose because they cannot buy the good
• Producers lose surplus
• Deadweight loss (DWL) forms from lost trades between Qs and Qe

Non-price rationing often appears:

• Long lines
• Favoritism
• Black markets

Rent control is the classic example. Over time it can reduce apartment quality and discourage new construction.

Price Floor Effects

When price is forced above equilibrium:

• Qs increases, Qd decreases
• Surplus = Qs − Qd
• Some producers gain (higher price)
• Others cannot sell their output
• Consumer surplus falls
• Deadweight loss from inefficient overproduction

The gap between Q_d and Q_s at the price floor represents the surplus.

In agriculture, the government has historically purchased excess crops to maintain price supports. Minimum wage laws create a surplus of labor, which we interpret as unemployment.

Efficiency Rule

If the market was already producing the efficient quantity, any binding price control reduces allocative efficiency and creates DWL.

3. Taxes and Subsidies

Governments also intervene through per-unit (excise) taxes and per-unit subsidies.

Per-Unit (Excise) Tax

An excise tax is charged on each unit sold. It increases production costs and shifts supply left (up).

Excise tax: tax wedge, revenue, and deadweight loss

In the graph, the original supply curve shifts upward. The price consumers pay rises to $P_1$, the price producers receive falls to $P_2$, and the quantity decreases from $Q_0$ to $Q_1$. The vertical distance between the two prices is the per-unit tax.

Effects:

• Consumers pay higher price $P_c$
• Producers receive lower price $P_p$
• The vertical wedge equals the tax
• Quantity decreases

Tax revenue

$$\text{Tax revenue} = \text{tax} \times \text{quantity sold}$$

On the graph, this is the rectangle formed by the tax wedge and the new quantity $Q_1$.

Deadweight loss is the small triangle to the right of the tax revenue rectangle, created by the reduction in quantity from $Q_0$ to $Q_1$.

Example: Cigarette taxes raise revenue and reduce smoking.

Quick calculation example: If tax = 4 dollars and new quantity = 500 units, revenue = $4 \times 500 = 2000$ dollars.

Excise vs. Lump-Sum Tax

A lump-sum tax is a fixed amount independent of quantity. For AP, focus on excise taxes because they change marginal cost and shift supply.

Per-Unit Subsidy

A subsidy is a payment per unit.

• Shifts supply right (down) if given to producers
• Lowers consumer price
• Raises producer price received
• Increases quantity

Government cost

$$\text{Subsidy cost} = \text{subsidy} \times \text{quantity}$$

Subsidies create DWL from overproduction. Farm subsidies are a common example.

4. Tax Incidence and Elasticity

Tax incidence refers to who bears the burden of a tax.

The key rule:

The more inelastic side of the market bears more of the tax burden.

Mnemonic: EPIC
Elastic demand → burden on Producers
Inelastic demand → burden on Consumers

Gasoline in the short run is relatively inelastic, so consumers bear much of the burden of gas taxes.

Elasticity explains why the price consumers pay usually rises by less than the full tax. The burden is shared.

5. Big Picture Effects of Government Intervention

All policies change incentives:

• Price ceilings → more consumption, less production
• Price floors → more production, less consumption
• Taxes → discourage production and consumption
• Subsidies → encourage both

When intervention occurs in a market that was already efficient:

• Total surplus falls
• Deadweight loss represents the lost gains from trade
• Government gains revenue (tax) or pays cost (subsidy), but society as a whole loses efficiency

On graph questions, you’re usually asked to:

• Identify if the policy is binding
• Show curve shifts
• Label Pc and Pp
• Calculate revenue or DWL
• Use elasticity to determine who bears the burden

Every policy works through incentives. Change the price signal, and behavior changes.