Supply, Demand, and the Benchmark Competitive Equilibrium

Introduction to Competitive Markets

Competitive markets are central to microeconomics, describing environments where buyers and sellers interact to determine prices and quantities of goods and services. In a perfectly competitive market, all sellers offer identical products, and no individual buyer or seller can influence the market price.

• Perfect Competition: Many buyers and sellers, identical goods, and no single agent can affect the price.

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

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

Example: The New York Stock Exchange is a classic example of a competitive market, where many buyers and sellers interact simultaneously.

Markets and Market Structures

A market consists of economic agents trading goods or services according to established rules. Examples include agricultural markets, stock exchanges, and car dealerships.

• Market Structure: The organization and characteristics of a market, such as the number of buyers and sellers and the nature of the product.

Example: Local farmers' markets and used car lots are examples of markets with different structures.

Demand: How Buyers Behave

Quantity Demanded, Demand Schedules, and Demand Curves

The quantity demanded is the amount of a good buyers are willing to purchase at a given price. A demand schedule is a table showing quantities demanded at various prices, while the demand curve graphically represents this relationship.

• Law of Demand: As price falls, quantity demanded generally rises (ceteris paribus).

• Market Demand Curve: The horizontal sum of all individual demand curves in the market.

Mathematical Representation of Demand

Demand can be expressed as a function:

• General form:

• Example:

• Inverse demand:

Aggregation of Demand

The market demand curve is derived by summing individual demand curves horizontally at each price level.

Shifts in the Demand Curve

Demand curves shift due to changes in non-price factors:

• Tastes and Preferences

• Income and Wealth (Normal vs. Inferior Goods)

• Prices of Related Goods (Substitutes and Complements)

• Number and Scale of Buyers

• Expectations about the Future

Movement Along vs. Shift of the Demand Curve

A movement along the demand curve is caused only by a change in the good's own price, while shifts are caused by changes in other factors.

Supply: How Sellers Behave

Quantity Supplied, Supply Schedules, and Supply Curves

The quantity supplied is the amount of a good sellers are willing to sell at a given price. A supply schedule lists quantities supplied at different prices, and the supply curve plots this relationship.

• Law of Supply: As price rises, quantity supplied generally rises (ceteris paribus).

• Market Supply Curve: The horizontal sum of all individual supply curves.

Aggregation of Supply

Market supply is found by summing individual supply schedules horizontally at each price.

Shifts in the Supply Curve

Supply curves shift due to changes in:

• Input Prices

• Technology

• Number and Scale of Sellers

• Expectations about the Future

Technological Change and Supply

Technological improvements can shift the supply curve to the right, increasing quantity supplied at each price.

Market Equilibrium

Competitive Equilibrium

The competitive equilibrium is the point where the market demand and supply curves intersect, determining the equilibrium price and quantity.

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

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

Shifts in Supply and Demand and Their Effects on Equilibrium

Changes in supply or demand shift the equilibrium price and quantity. For example, a leftward shift in supply (e.g., due to higher input costs) raises price and lowers quantity, while a rightward shift lowers price and increases quantity.

Applications: Case Studies in Supply and Demand

Why Do Brown Eggs Cost More Than White Eggs?

Brown eggs often cost more due to higher production costs (the hens are larger and eat more). The supply curve for brown eggs is to the left of that for white eggs, reflecting higher costs and lower quantity supplied at each price. Nutritional content is similar, so demand differences are minimal.

Why Do Rose Prices Increase Before Valentine’s Day?

Rose prices rise before Valentine’s Day due to a rightward shift in the demand curve (increased demand for roses as gifts). The supply curve remains relatively stable, so the equilibrium price increases.

Mathematical Example: Finding Equilibrium Algebraically

Suppose demand and supply are given by:

• Demand:

• Supply:

Set to find equilibrium:

Interpretation: At a price of 6, both quantity demanded and supplied are 4 units, so the market is in equilibrium.

Practice Problems

• Draw demand and supply curves for various scenarios (e.g., perfectly inelastic demand, single buyer, negative equilibrium price).

• Analyze the effects of simultaneous shifts in demand and supply (e.g., umbrellas during a wet spring and supply chain disruptions).

• Calculate new equilibrium when demand triples or supply changes.

Summary Table: Factors Shifting Demand and Supply

Additional info: This guide covers the foundational concepts of supply, demand, and market equilibrium, with applications and mathematical examples relevant for introductory microeconomics students.