Demand, Supply, and Equilibrium

Introduction

This chapter explores the core mechanisms of microeconomic markets: demand, supply, and equilibrium. It examines how buyers and sellers interact, how prices are determined, and the effects of government intervention in markets. Understanding these concepts is essential for analyzing real-world economic issues and policy debates.

Markets

Definition and Structure of Markets

• Market: A group of economic agents trading a good or service, along with the rules and arrangements for trading.

• Markets may have a physical location (e.g., a supermarket) or be virtual (e.g., online marketplaces).

• Market Price: The price at which buyers and sellers conduct transactions.

In a perfectly competitive market:

• All sellers offer an identical good or service.

• No individual buyer or seller can influence the market price.

• All transactions occur at the same market price.

Prices act as a selection device, encouraging trade between sellers who can produce at low cost and buyers who value the good highly.

How Do Buyers Behave?

Demand, Demand Schedules, and Demand Curves

• Quantity Demanded: The amount of a good buyers are willing to purchase at a given price.

• Demand Schedule: A table reporting quantity demanded at different prices, holding all else equal.

• Demand Curve: A graph plotting quantity demanded at various prices.

Market Demand and the Law of Demand

• Market Demand Curve: The sum of all individual demand curves; shows total quantity demanded at each price.

• Law of Demand: In almost all cases, quantity demanded rises as price falls (holding all else equal).

Shifts vs. Movements Along the Demand Curve

• Movement along the demand curve: Caused only by a change in the good’s own price.

• Shift of the demand curve: Caused by changes in:

  • Tastes and preferences

  • Income and wealth

  • Availability and prices of related goods (substitutes and complements)

  • Number and scale of buyers

  • Buyers’ expectations about the future

Types of Goods

• Normal Goods: Demand increases as income rises.

• Inferior Goods: Demand decreases as income rises.

Related Goods

• Substitutes: Goods that can replace each other; an increase in the price of one increases demand for the other.

• Complements: Goods used together; an increase in the price of one decreases demand for the other.

How Do Sellers Behave?

Supply, Supply Schedules, and Supply Curves

• Quantity Supplied: The amount of a good sellers are willing to sell at a given price.

• Supply Schedule: A table reporting quantity supplied at different prices.

• Supply Curve: A graph plotting quantity supplied at various prices.

Market Supply and the Law of Supply

• Market Supply Curve: The sum of all individual supply curves; shows total quantity supplied at each price.

• Law of Supply: In almost all cases, quantity supplied rises as price rises (holding all else equal).

Shifts vs. Movements Along the Supply Curve

• Movement along the supply curve: Caused only by a change in the good’s own price.

• Shift of the supply curve: Caused by changes in:

  • Input prices

  • Technology

  • Number and scale of sellers

  • Sellers’ expectations about the future

Examples of Supply Shifters

• Input Prices: Higher input costs decrease supply (shift left); lower input costs increase supply (shift right).

• Technology: Technological improvements increase supply (shift right).

• Number of Sellers: More sellers increase supply (shift right); fewer sellers decrease supply (shift left).

• Expectations: If sellers expect higher future prices, they may decrease current supply.

Supply and Demand in Equilibrium

Competitive Equilibrium

• Competitive Equilibrium: The price and quantity at which quantity demanded equals quantity supplied.

• At equilibrium, the market "clears"—there is neither excess demand nor excess supply.

Excess Demand and Excess Supply

• Excess Demand (Shortage): Quantity demanded exceeds quantity supplied at a given price.

• Excess Supply (Surplus): Quantity supplied exceeds quantity demanded at a given price.

Curve Shifting in Equilibrium

• Shifts in demand or supply curves change the equilibrium price and quantity.

• Simultaneous shifts in both curves can have complex effects on equilibrium.

Examples and Applications

• Why do brown eggs cost more than white eggs? (Supply side: higher production costs; Demand side: perceived health benefits)

• Why do rose prices rise before Valentine’s Day? (Rightward shift in demand)

• Why doesn’t beer price rise before Super Bowl Sunday? (Both demand and supply shift right)

• Parking problems on campus: price controls can prevent market clearing.

Government Intervention: Price Controls

Price Ceilings and Floors

• When governments set maximum (ceiling) or minimum (floor) prices, markets may not clear.

• Example: U.S. gasoline price cap during the 1973–1974 oil crisis led to shortages.

Evidence-Based Economics: Gasoline Demand and Policy

• Lower gasoline prices (due to subsidies) increase quantity demanded; higher prices (due to taxes) decrease quantity demanded.

• Moving between countries with different gasoline prices causes movement along the demand curve, not a shift.

• Changes in preferences (e.g., new interest in road trips) shift the demand curve.

Key Terms and Formulas

• Demand Function: Where = quantity demanded, = price, = income, = price of related goods, = tastes, = expectations.

• Supply Function: Where = quantity supplied, = price, = input prices, = technology, = number of sellers, = expectations.

• Equilibrium Condition:

Summary Table: Factors Shifting Demand and Supply

Conclusion

Understanding demand, supply, and equilibrium is fundamental to microeconomics. These concepts explain how prices are determined, how markets allocate resources, and how government policies can impact market outcomes. Mastery of these topics provides a foundation for analyzing more complex economic phenomena.