Microeconomics Study Notes: Chapter 3 – Where Prices Come From: Interaction of Supply and Demand

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Chapter 3: Where Prices Come From – Interaction of Supply and Demand

Overview

This chapter explores the fundamental microeconomic concepts of supply and demand, focusing on how prices are determined in competitive markets. Understanding these basics is essential for analyzing more complex market behaviors in later chapters.

The Demand Side of the Market

Market Demand and Its Determinants

Market demand refers to the total quantity of a good or service that all consumers are willing and able to purchase at various prices.

Demand Schedule: A table showing the relationship between the price of a product and the quantity demanded.
Demand Curve: A graphical representation of the demand schedule, typically downward sloping, indicating the inverse relationship between price and quantity demanded.
Ceteris Paribus: The assumption that all other variables are held constant when analyzing the effect of price on quantity demanded.
Quantity Demanded: The amount of a good or service that a consumer is willing and able to purchase at a given price.
Law of Demand: Holding everything else constant, when the price of a product falls, the quantity demanded increases; when the price rises, the quantity demanded decreases.

Example: If the price of Nike shoes decreases, more consumers will be willing to buy them, increasing the quantity demanded.

Why Does the Law of Demand Hold?

Substitution Effect: Consumers switch to the good whose price has fallen, making it relatively less expensive compared to other goods.
Income Effect: A lower price increases consumers' purchasing power, allowing them to buy more.

Shifts in the Demand Curve

A change in a non-price determinant of demand causes the entire demand curve to shift.

Increase in Demand: Demand curve shifts right.
Decrease in Demand: Demand curve shifts left.

Variables That Shift Demand:

Income of Consumers: Demand for normal goods increases with income; demand for inferior goods decreases with income.
Prices of Related Goods: Substitutes (increase in price of one increases demand for the other); Complements (increase in price of one decreases demand for the other).
Tastes: Changes in consumer preferences can increase or decrease demand.
Population and Demographics: Changes in population size or composition affect demand.
Expectations: Expectations about future prices can shift current demand.

Example: If consumers expect the price of gasoline to rise tomorrow, demand today increases.

Change in Demand vs. Change in Quantity Demanded

Change in Quantity Demanded: Movement along the demand curve due to a change in price.
Change in Demand: Shift of the entire demand curve due to changes in other factors.

The Supply Side of the Market

Market Supply and Its Determinants

Market supply refers to the total quantity of a good or service that all firms are willing and able to sell at various prices.

Supply Schedule: A table showing the relationship between the price of a product and the quantity supplied.
Supply Curve: A graphical representation of the supply schedule, typically upward sloping, indicating the direct relationship between price and quantity supplied.
Quantity Supplied: The amount of a good or service that a firm is willing and able to supply at a given price.
Law of Supply: Holding everything else constant, increases in price cause increases in quantity supplied; decreases in price cause decreases in quantity supplied.

Shifts in the Supply Curve

A change in a non-price determinant of supply causes the entire supply curve to shift.

Increase in Supply: Supply curve shifts right.
Decrease in Supply: Supply curve shifts left.

Variables That Shift Supply:

Prices of Inputs: Higher input prices decrease supply; lower input prices increase supply.
Technological Change: Improvements increase supply; restrictions decrease supply.
Prices of Substitutes in Production: If the price of a substitute rises, supply of the original good may decrease.
Number of Firms: More firms increase supply; fewer firms decrease supply.
Expected Future Prices: If firms expect higher prices in the future, they may decrease current supply.

Change in Supply vs. Change in Quantity Supplied

Change in Quantity Supplied: Movement along the supply curve due to a change in price.
Change in Supply: Shift of the entire supply curve due to changes in other factors.

Market Equilibrium: Putting Buyers and Sellers Together

Market Equilibrium

Market equilibrium occurs when quantity demanded equals quantity supplied. The corresponding price is the equilibrium price, and the quantity is the equilibrium quantity.

Surplus: Occurs when quantity supplied exceeds quantity demanded at a given price; leads to downward pressure on price.
Shortage: Occurs when quantity demanded exceeds quantity supplied at a given price; leads to upward pressure on price.

Example: If the price of athletic shoes is above equilibrium, a surplus results and price falls. If below equilibrium, a shortage results and price rises.

The Effect of Demand and Supply Shifts on Equilibrium

Predicting Changes in Price and Quantity

Shifts in demand and/or supply curves affect equilibrium price and quantity. The direction of change depends on which curve shifts and by how much.

Demand Curve	Supply Curve Unchanged	Supply Curve Shifts Right	Supply Curve Shifts Left
Unchanged	P unchanged, Q unchanged	P decreases, Q increases	P increases, Q decreases
Shifts Right	P increases, Q increases	P may increase or decrease, Q increases	P increases, Q may increase or decrease
Shifts Left	P decreases, Q decreases	P decreases, Q may increase or decrease	P may increase or decrease, Q decreases

Example: If a new firm enters the athletic shoe market (supply increases), equilibrium price falls and quantity rises. If consumer incomes rise (demand increases for normal goods), both equilibrium price and quantity rise.

Shifts of a Curve vs. Movements Along a Curve

Movement Along a Curve: Caused by a change in the good's own price.
Shift of a Curve: Caused by changes in other determinants (income, tastes, input prices, etc.).

Common Misconceptions:

Confusing movement along a curve with a shift of the curve.
Assuming both price and quantity changes are always certain when both curves shift; often only one is certain.
Not labeling diagrams or arrows clearly in graphical analysis.

Key Formulas and Equations

Law of Demand: , where is quantity demanded and is price.
Law of Supply: , where is quantity supplied and is price.
Equilibrium Condition:

Applications and Examples

Real-World Example: The impact of a celebrity's injury on Nike's demand, or the effect of COVID-19 on athletic shoe sales, illustrates how tastes and external events shift demand curves.
Demographics: Millennials and Gen Z have different preferences, affecting demand for products like athletic shoes.

Additional info: These notes expand on brief slide points to provide full academic context, definitions, and examples for self-contained study.