Core Concepts & Learning Goals
This topic explores how a domestic market for a good or service is affected when a country opens its economy to international trade. The price of a good on the global market—the world price—can be higher or lower than the domestic price that would exist without trade. This difference creates opportunities for imports or exports, which in turn affects prices, quantities, and the economic welfare of consumers and producers.
We will also analyze how public policies, specifically tariffs and quotas, are used to restrict international trade. While these policies can protect domestic industries, they also create market inefficiencies. After studying this topic, you should be able to define these policies, use supply and demand graphs to explain their effects on market outcomes, and calculate the resulting changes to consumer surplus, producer surplus, government revenue, and total economic surplus.
Key Concepts Breakdown
1. From a Closed to an Open Economy
A country's economy before it engages in international trade is in a state of autarky. In this state, the equilibrium price and quantity of a good are determined solely by domestic supply and domestic demand.
When an economy opens to trade, the relevant price becomes the world price (Pw), which is the price of a good prevailing in the global market.
If the World Price is Below the Domestic Price (Pw < P_autarky):
The country will become an importer of the good.
Domestic consumers will benefit from the lower price, so the quantity they demand will increase.
Domestic producers will be hurt by the lower price, so the quantity they supply will decrease.
The difference between the quantity demanded by domestic consumers and the quantity supplied by domestic producers is filled by imports.
Welfare Effect: Consumer surplus increases by more than producer surplus decreases, leading to an overall increase in total economic surplus for the country.
If the World Price is Above the Domestic Price (Pw > P_autarky):
The country will become an exporter of the good.
Domestic producers will benefit from the higher price, so the quantity they supply will increase.
Domestic consumers will be hurt by the higher price, so the quantity they demand will decrease.
The difference between the quantity supplied by domestic producers and the quantity demanded by domestic consumers is exported.
Welfare Effect: Producer surplus increases by more than consumer surplus decreases, leading to an overall increase in total economic surplus.
2. Tariffs: A Tax on Imports
Governments may seek to protect domestic producers from lower-priced foreign competition by implementing a tariff. A tariff is a tax levied on an imported good.
The primary effects of a tariff are:
Price: The domestic price of the good increases from the world price (Pw) to the price with the tariff (Pt), where ( P_t = P_w + \text{tariff} ).
Quantities:
The higher domestic price causes the quantity demanded by domestic consumers to decrease.
The higher domestic price causes the quantity supplied by domestic producers to increase.
The quantity of imports shrinks.
Welfare and Revenue:
Consumer Surplus: Decreases due to the higher price and lower quantity consumed.
Producer Surplus: Increases due to the higher price and higher quantity supplied by domestic firms.
Government Revenue: The government collects revenue equal to the tariff amount multiplied by the new, lower quantity of imports.
Total Surplus: Decreases. The losses to consumer surplus are greater than the gains in producer surplus and government revenue. The net loss in total surplus is called deadweight loss (DWL).
3. Quotas: A Limit on Imports
Another way to restrict trade is with a quota, which is a legal limit on the quantity of a good that can be imported.
While the graphing of quotas is not required, their effects are important to understand. By physically limiting the number of imported goods, a quota restricts the total supply available in the domestic market.
The primary effects of a quota are:
Price: The restriction in supply causes the domestic price of the good to rise above the world price.
Quantities:
The higher domestic price causes the quantity demanded by domestic consumers to decrease.
The higher domestic price causes the quantity supplied by domestic producers to increase.
Welfare:
Consumer Surplus: Decreases.
Producer Surplus: Increases.
Total Surplus: Decreases, creating deadweight loss. Unlike a tariff, a quota does not generate revenue for the government.
Graphical Analysis (Text-Only)
This analysis focuses on the case of a country importing a good where the world price (Pw) is below the domestic autarky price, and the government imposes a tariff.
Market Setup
Vertical axis: Price (P)
Horizontal axis: Quantity (Q)
Curves:
Domestic Demand (Dd): A downward-sloping line.
Domestic Supply (Ds): An upward-sloping line.
World Price (Pw): A horizontal line positioned below the intersection of Ds and Dd.
Price with Tariff (Pt): A horizontal line positioned above Pw but below the intersection of Ds and Dd.
Analysis Steps: From Free Trade to a Tariff
Free Trade Equilibrium (No Tariff):
The market price is the world price, Pw.
At Pw, find the domestic quantity supplied (Qs1) where the Pw line intersects the Ds curve.
At Pw, find the domestic quantity demanded (Qd1) where the Pw line intersects the Dd curve.
The quantity of imports is the horizontal distance between these two points: ( \text{Imports} = Qd1 - Qs1 ).
Consumer Surplus (CS): The large triangle below the Dd curve and above the Pw line, out to quantity Qd1.
Producer Surplus (PS): The triangle above the Ds curve and below the Pw line, out to quantity Qs1.
Imposing a Tariff:
The government imposes a tariff, raising the domestic price to Pt.
At the new, higher price Pt, find the new domestic quantity supplied (Qs2) where the Pt line intersects the Ds curve. Note that Qs2 > Qs1.
At Pt, find the new domestic quantity demanded (Qd2) where the Pt line intersects the Dd curve. Note that Qd2 < Qd1.
The new, smaller quantity of imports is ( \text{Imports} = Qd2 - Qs2 ).
Welfare Analysis with a Tariff:
New Consumer Surplus: The smaller triangle below the Dd curve and above the Pt line, out to quantity Qd2. The loss in CS is the trapezoidal area between Pt and Pw.
New Producer Surplus: The larger triangle above the Ds curve and below the Pt line, out to quantity Qs2. The gain in PS is the trapezoid area between Pt and Pw, to the left of the Ds curve.
Government Revenue: A rectangle with height ( (P_t - P_w) ) and width ( (Qd2 - Qs2) ). This area was previously part of consumer surplus.
Deadweight Loss (DWL): Two triangles representing the net loss to society.
Triangle 1 (Production Inefficiency): Located between quantities Qs1 and Qs2, above the Ds curve and below the Pt line. This represents the loss from domestic producers making the good at a higher cost than the world price.
Triangle 2 (Consumption Inefficiency): Located between quantities Qd2 and Qd1, below the Dd curve and above the Pt line. This represents the loss from consumers who are no longer able to buy the good at the higher price, even though they valued it more than the world price.
Step-by-Step Example
Consider the market for bicycles. Domestic demand is ( P = 220 - Q_d ) and domestic supply is ( P = 40 + 2Q_s ). The world price for a bicycle is $60. The government imposes a $20 tariff on each imported bicycle.
Step 1: Analyze the Market with Free Trade
At the world price ( P_w = $60 ):
Domestic Quantity Demanded: ( 60 = 220 - Q_d \implies Q_d = 160 )
Domestic Quantity Supplied: ( 60 = 40 + 2Q_s \implies 20 = 2Q_s \implies Q_s = 10 )
Quantity of Imports: ( 160 - 10 = 150 ) bicycles.
Step 2: Analyze the Market with the Tariff
The tariff raises the domestic price to ( P_t = P_w + \text{tariff} = $60 + $20 = $80 ).
At the new price ( P_t = $80 ):
New Domestic Quantity Demanded: ( 80 = 220 - Q_d \implies Q_d = 140 )
New Domestic Quantity Supplied: ( 80 = 40 + 2Q_s \implies 40 = 2Q_s \implies Q_s = 20 )
New Quantity of Imports: ( 140 - 20 = 120 ) bicycles.
Step 3: Calculate the Changes in Surplus and Revenue
Change in Consumer Surplus (CS): CS is lost. The area of the trapezoid is ( \frac{1}{2} \times (\text{base}_1 + \text{base}_2) \times \text{height} ). Here, the "height" is the price change ($80 - $60 = $20). The "bases" are the quantities demanded.
- Loss of CS = ( \frac{1}{2} \times (140 + 160) \times ($20) = $3,000 )
Change in Producer Surplus (PS): PS is gained. This is the trapezoid area between the old and new price, bounded by the supply curve.
- Gain in PS = ( \frac{1}{2} \times (10 + 20) \times ($20) = $300 )
Government Revenue: The tariff amount multiplied by the quantity of imports.
- Revenue = ( $20/\text{bicycle} \times 120 \text{ bicycles} = $2,400 )
Deadweight Loss (DWL): The loss in CS that is not transferred to producers or the government.
DWL = Loss in CS - (Gain in PS + Gov Revenue)
DWL = ( $3,000 - ($300 + $2,400) = $300 )
Alternatively, calculate the two DWL triangles:
Production DWL = ( \frac{1}{2} \times (20 - 10) \times ($20) = $100 )
Consumption DWL = ( \frac{1}{2} \times (160 - 140) \times ($20) = $200 )
Total DWL = ( $100 + $200 = $300 )
AP Exam Tips & Common Pitfalls
[FRQ Task]: A common Free-Response Question involves a fully labeled graph of a market with a world price. You may be asked to identify the quantity of imports and then calculate the effects of a tariff on price, quantity, consumer surplus, producer surplus, government revenue, and deadweight loss.
[MCQ Task]: Multiple-choice questions often test your understanding of who wins and who loses from trade policies. For example: "When a tariff is imposed on a good, which of the following will occur?" The answer will relate to domestic producers benefiting and domestic consumers being harmed.
[Common Pitfall ①]: Misidentifying the quantity of imports. Students sometimes mistakenly label the total quantity demanded (Qd) as the quantity of imports. Remember, imports are the difference between what domestic consumers demand and what domestic producers supply at the world price (or tariff price).
[Common Pitfall ②]: Calculating government revenue incorrectly. The revenue from a tariff is the per-unit tariff amount multiplied by the quantity of imports after the tariff is imposed, not the original quantity of imports.
Key Vocabulary
Autarky: A state in which a country does not engage in international trade; a closed economy.
World Price: The price of a good or service that prevails in the global market.
Tariff: A tax imposed by a government on an imported good.
Quota: A legal limit on the quantity of a good that is permitted to be imported.
Deadweight Loss (DWL): The reduction in total economic surplus resulting from a market distortion, such as a tax, tariff, or quota.