The Basics of Supply and Demand: Intermediate Microeconomics Study Notes

The Basics of Supply and Demand

Introduction

Supply and demand analysis is a foundational tool in microeconomics, used to understand and predict how changes in market conditions affect prices and production. This chapter explores the mechanics of supply and demand, market equilibrium, elasticity, and the effects of government intervention.

2.1 Supply and Demand

The Supply Curve

• Definition: The supply curve shows the relationship between the quantity of a good that producers are willing to sell and the price of the good.

• Law of Supply: As the price of a good increases, the quantity supplied generally increases, ceteris paribus (all else equal).

• Equation: $Q_s = Q_s(P)$, where $Q_s$ is quantity supplied and $P$ is price.

• Other Variables Affecting Supply: Input prices, technology, expectations, and the number of sellers can shift the supply curve.

The Demand Curve

• Definition: The demand curve shows the relationship between the quantity of a good that consumers are willing to buy and the price of the good.

• Law of Demand: As the price of a good increases, the quantity demanded generally decreases, ceteris paribus.

• Equation: $Q_d = Q_d(P)$, where $Q_d$ is quantity demanded and $P$ is price.

Inverse Demand Curve

• Expresses the demand curve in terms of price as a function of quantity.

• Example: If $Q = 80 - 2P$, then $P = 40 - 0.5Q$.

Shifting the Demand Curve

• Income: An increase in income shifts the demand curve for a normal good to the right.

• Prices of Related Goods: The demand for a good increases if the price of a substitute rises, and decreases if the price of a complement rises.

2.2 The Market Mechanism

Market Equilibrium

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

• Market Mechanism: The tendency for prices to adjust until the market clears (no shortage or surplus).

• Surplus: Quantity supplied exceeds quantity demanded at a given price.

• Shortage: Quantity demanded exceeds quantity supplied at a given price.

Application: Shortages in Real Life

• Example: Drug shortages of 2012 illustrate how supply and demand imbalances can lead to real-world shortages.

2.3 Changes in Market Equilibrium

Shifts in Supply and Demand

• Changes in supply or demand shift the respective curves, leading to new equilibrium prices and quantities.

• Example: An increase in demand shifts the demand curve right, raising both equilibrium price and quantity.

• Example: An increase in supply shifts the supply curve right, lowering equilibrium price and raising quantity.

Case Studies

• The Price of Eggs and College Education: Changes in supply and demand explain long-term trends in prices for different markets.

• Wage Inequality: Shifts in labor supply and demand can explain changes in wage distribution.

2.4 Elasticities of Supply and Demand

Elasticity

• Definition: Elasticity measures the percentage change in one variable resulting from a 1% change in another variable.

Price Elasticity of Demand

• Formula: $E_d = \frac{\Delta Q}{\Delta P} \cdot \frac{P}{Q}$

• Along a linear demand curve $Q = a - bP$, elasticity at a point is $E_d = -b \cdot \frac{P}{Q}$

• Interpretation: If $|E_d| > 1$, demand is elastic; if $|E_d| < 1$, demand is inelastic.

Other Elasticities

• Income Elasticity of Demand: $E_I = \frac{\Delta Q}{\Delta I} \cdot \frac{I}{Q}$

• Cross-Price Elasticity of Demand: $E_{xy} = \frac{\Delta Q_x}{\Delta P_y} \cdot \frac{P_y}{Q_x}$

• Price Elasticity of Supply: $E_s = \frac{\Delta Q_s}{\Delta P} \cdot \frac{P}{Q_s}$

Point vs. Arc Elasticity

• Point Elasticity: Measures elasticity at a specific point on the curve.

• Arc Elasticity: Measures elasticity over a range of prices/quantities.

• Arc Elasticity Formula: $E_{arc} = \frac{\Delta Q}{\Delta P} \cdot \frac{P_1 + P_2}{Q_1 + Q_2}$

2.5 Short-Run versus Long-Run Elasticities

• Elasticities can differ in the short run and long run due to adjustment lags in consumer and producer behavior.

• Example: Demand for gasoline is more elastic in the long run as consumers can adjust their habits.

2.6 Understanding and Predicting the Effects of Changing Market Conditions

• Simultaneous shifts in supply and demand can be analyzed using comparative statics to predict new equilibrium outcomes.

• Practice Problem: Calculating new equilibrium when both curves shift.

2.7 Effects of Government Intervention—Price Controls

• Price Ceiling: A legal maximum price, leading to shortages if set below equilibrium.

• Price Floor: A legal minimum price, leading to surpluses if set above equilibrium.

• Example: Price controls and natural gas shortages.

Real vs. Nominal Prices

• Nominal Price: The current dollar price of a good or service.

• Real Price: The price adjusted for inflation, reflecting purchasing power.

• Formula: $\text{Real Price in year t (in base year dollars)} = \text{Nominal Price in year t} \times \frac{\text{CPI in base year}}{\text{CPI in year t}}$

• Application: Comparing prices across time periods requires adjusting for inflation using the Consumer Price Index (CPI).

Practice Problems and Applications

• Numerous practice problems are provided throughout, including calculating equilibrium, elasticity, and the effects of government intervention.

• Real-world examples such as the market for wheat, coffee, and the effects of weather and policy changes are discussed.

Summary Table: Key Elasticity Formulas

Elasticity Type	Formula	Interpretation
Price Elasticity of Demand	$E_d = \frac{\Delta Q}{\Delta P} \cdot \frac{P}{Q}$	Responsiveness of quantity demanded to price changes
Income Elasticity of Demand	$E_I = \frac{\Delta Q}{\Delta I} \cdot \frac{I}{Q}$	Responsiveness of quantity demanded to income changes
Cross-Price Elasticity	$E_{xy} = \frac{\Delta Q_x}{\Delta P_y} \cdot \frac{P_y}{Q_x}$	Responsiveness of demand for good x to price changes in good y
Price Elasticity of Supply	$E_s = \frac{\Delta Q_s}{\Delta P} \cdot \frac{P}{Q_s}$	Responsiveness of quantity supplied to price changes

Additional info: These notes expand on the provided slides by including definitions, formulas, and examples for clarity and completeness. All equations are presented in LaTeX format for academic rigor.