Macroeconomics Study Guide: Demand, Supply, Market Equilibrium, and Trade

Review Topics: Chapters 3, 4, and 7

Law of Demand and Law of Supply

The Law of Demand and Law of Supply are foundational principles in economics that describe how the quantity demanded or supplied of a good changes in response to price changes.

• Law of Demand: As the price of a good increases, the quantity demanded decreases, ceteris paribus (all else equal). Conversely, as the price decreases, the quantity demanded increases.

• Law of Supply: As the price of a good increases, the quantity supplied increases, ceteris paribus. As the price decreases, the quantity supplied decreases.

• Shifters of Demand: Factors other than price that can shift the demand curve, such as income, tastes, prices of related goods, expectations, and number of buyers.

• Shifters of Supply: Factors other than price that can shift the supply curve, such as input prices, technology, expectations, and number of sellers.

Example: If consumer incomes rise (assuming a normal good), the demand curve shifts to the right, increasing equilibrium price and quantity.

Changes in Quantity Demanded/Supplied vs. Changes in Demand/Supply

It is important to distinguish between movements along a curve and shifts of the curve:

• Change in Quantity Demanded (Qd): Movement along the demand curve due to a change in the good's own price.

• Change in Demand: Shift of the entire demand curve due to a non-price determinant.

• Change in Quantity Supplied (Qs): Movement along the supply curve due to a change in the good's own price.

• Change in Supply: Shift of the entire supply curve due to a non-price determinant.

Example: A decrease in the price of a substitute good shifts the demand curve for the original good to the left (decrease in demand).

Market Equilibrium

Equilibrium occurs where the quantity demanded equals the quantity supplied. The corresponding price is the equilibrium price, and the quantity is the equilibrium quantity.

• Shortage: Occurs when quantity demanded exceeds quantity supplied at a given price (price below equilibrium).

• Surplus: Occurs when quantity supplied exceeds quantity demanded at a given price (price above equilibrium).

Equation:

$Q_d = Q_s$

Example: If the market price is set above equilibrium, a surplus results, putting downward pressure on price.

Price Controls

Price controls are government-imposed limits on the prices that can be charged in the market.

• Price Ceiling: A legal maximum price (e.g., rent control). If set below equilibrium, causes a shortage.

• Price Floor: A legal minimum price (e.g., minimum wage). If set above equilibrium, causes a surplus.

Consumer and Producer Surplus

Consumer Surplus is the difference between what consumers are willing to pay and what they actually pay. Producer Surplus is the difference between the price producers receive and the minimum they are willing to accept.

• Consumer Surplus Formula:

$\text{Consumer Surplus} = \text{Willingness to Pay} - \text{Price Paid}$

• Producer Surplus Formula:

$\text{Producer Surplus} = \text{Price Received} - \text{Cost to Seller}$

Deadweight Loss

Deadweight loss is the loss of total surplus that occurs when the market is not in equilibrium, often due to price controls or taxes.

Tax Incidence and Impact of Tax

Tax incidence refers to how the burden of a tax is distributed between buyers and sellers. The impact depends on the relative elasticities of demand and supply.

• Tax on Buyers: Shifts the demand curve downward by the amount of the tax.

• Tax on Sellers: Shifts the supply curve upward by the amount of the tax.

• Burden: The side of the market (buyers or sellers) that is less elastic bears more of the tax burden.

Equation:

$\text{Tax Burden on Buyers} = \frac{E_s}{E_s + |E_d|} \times \text{Tax}$ $\text{Tax Burden on Sellers} = \frac{|E_d|}{E_s + |E_d|} \times \text{Tax}$

Example: If demand is inelastic and supply is elastic, buyers bear most of the tax burden.

Trade

Trade allows countries to specialize in the production of goods for which they have a comparative advantage, increasing overall economic welfare.

• Opportunity Cost: The value of the next best alternative foregone when making a choice.

• Absolute Advantage: The ability to produce more of a good with the same resources than another producer.

• Comparative Advantage: The ability to produce a good at a lower opportunity cost than another producer.

• Terms of Trade: The rate at which one good is exchanged for another between countries.

Example: If Country A can produce either 10 cars or 20 computers, and Country B can produce either 5 cars or 15 computers, Country A has an absolute advantage in both, but the comparative advantage depends on opportunity costs.

Summary Table: Key Concepts

Concept	Definition	Example/Application
Law of Demand	Inverse relationship between price and quantity demanded	As price of coffee rises, fewer cups are sold
Law of Supply	Direct relationship between price and quantity supplied	As price of wheat rises, more wheat is produced
Consumer Surplus	Difference between willingness to pay and actual price	Buyer values a book at $20, pays $15, surplus is $5
Producer Surplus	Difference between price received and cost to seller	Seller's cost is $10, sells for $15, surplus is $5
Deadweight Loss	Loss of total surplus from market distortion	Tax reduces quantity traded below equilibrium
Comparative Advantage	Lower opportunity cost in production	Country A produces cars more efficiently than B