Supply, Demand, and Elasticity: Core Concepts in Microeconomics

Supply, Demand, and Elasticity

Introduction

This study guide covers the foundational concepts of supply, demand, and elasticity in microeconomics. These principles explain how markets function, how prices are determined, and how consumers and producers respond to changes in market conditions.

Shifts in Supply

Understanding Supply Shifts

• Supply refers to the quantity of a good or service that producers are willing and able to sell at various prices.

• Factors that affect supply include input costs, technological advancements, and government policies.

• A change in supply shifts the supply curve:

  • Rightward shift: Increase in supply (e.g., lower production costs, improved technology).

  • Leftward shift: Decrease in supply (e.g., higher input costs, adverse regulations).

• Graphically, a supply curve shift changes the equilibrium price and quantity.

Example: If a new technology reduces production costs, the supply curve shifts right, leading to a lower equilibrium price and higher equilibrium quantity.

Shifts in Demand

Understanding Demand Shifts

• Demand is the quantity of a good or service that consumers are willing and able to purchase at various prices.

• Factors affecting demand include changes in income, consumer tastes, prices of related goods, and network effects.

• A change in demand shifts the demand curve:

  • Rightward shift: Increase in demand (e.g., higher income, positive change in tastes).

  • Leftward shift: Decrease in demand (e.g., lower income, negative change in tastes).

• Graphically, a demand curve shift alters the equilibrium price and quantity.

Example: If consumer preferences shift toward electric cars, the demand curve for electric cars shifts right, increasing both equilibrium price and quantity.

Market Equilibrium

Defining Equilibrium

• Equilibrium price is the price at which quantity supplied equals quantity demanded.

• At equilibrium, there is no shortage or surplus in the market.

• Disequilibrium occurs when:

  • Shortage: Quantity demanded exceeds quantity supplied (price below equilibrium).

  • Surplus: Quantity supplied exceeds quantity demanded (price above equilibrium).

Example: If the market price is set below equilibrium, a shortage results, prompting upward pressure on price until equilibrium is restored.

Effects of Shifts on Equilibrium

Supply and Demand Shifts

• Increase in supply: Supply curve shifts right, equilibrium price falls, equilibrium quantity rises.

• Decrease in supply: Supply curve shifts left, equilibrium price rises, equilibrium quantity falls.

• Increase in demand: Demand curve shifts right, equilibrium price and quantity both rise.

• Decrease in demand: Demand curve shifts left, equilibrium price and quantity both fall.

• If both supply and demand shift, the effect on equilibrium price and quantity depends on the magnitude and direction of each shift.

Example: If both supply and demand increase, equilibrium quantity rises, but the effect on price depends on which shift is larger.

Algebraic Solution for Equilibrium

Solving Linear Supply and Demand Equations

• Supply and demand can be represented as linear equations:

  • Demand: $Q_d = a - bP$

  • Supply: $Q_s = c + dP$

• To find equilibrium:

  1. Set $Q_d = Q_s$

  2. Solve for equilibrium price $P^*$

  3. Substitute $P^*$ back into either equation to find equilibrium quantity $Q^*$

Example: If $Q_d = 100 - 2P$ and $Q_s = 20 + 3P$, set $100 - 2P = 20 + 3P$ and solve for $P$ and $Q$.

Elasticities of Supply and Demand

Price Elasticity of Demand

• Price elasticity of demand measures the responsiveness of quantity demanded to a change in price.

• Arc elasticity (over a range):

  • $E_p = (\Delta Q / \Delta P) (\overline{P} / \overline{Q})$

• Point elasticity (at a specific price):

  • $E_p = \frac{\Delta Q}{Q} / \frac{\Delta P}{P} = \frac{P \Delta Q}{Q \Delta P}$

• Elasticity varies along a linear demand curve; it is higher at higher prices and lower at lower prices.

Example: On a demand curve $Q = 8 - 2P$, elasticity at $P = 2$ is $E_p = -1$.

Types of Demand Elasticity

• Perfectly elastic demand: Consumers buy any quantity at a single price; elasticity is infinite.

• Perfectly inelastic demand: Consumers buy a fixed quantity regardless of price; elasticity is zero.

Example: Insulin for diabetics is often considered to have perfectly inelastic demand.

Income and Cross-Price Elasticities

• Income elasticity of demand: Measures the percentage change in quantity demanded resulting from a 1% change in income.

• Cross-price elasticity of demand: Measures the percentage change in quantity demanded of one good resulting from a 1% change in the price of another good.

Example: If the price of tea rises and the demand for coffee increases, coffee has positive cross-price elasticity with tea.

Short-Run vs. Long-Run Elasticities

Time Horizon Effects

• Elasticities can differ in the short run and long run due to adjustment periods.

• Demand for durable goods (e.g., cars) is more elastic in the long run as consumers have time to adjust their purchases.

• Supply of goods may be less elastic in the short run due to production constraints, but more elastic in the long run as firms can expand capacity.

Example: Gasoline demand is less elastic in the short run (limited alternatives), but more elastic in the long run as consumers switch to fuel-efficient cars.

Fitting Linear Supply and Demand Curves to Data

Estimating Curve Parameters

• Given equilibrium price ($P^*$) and quantity ($Q^*$), and estimates for elasticities, parameters for supply and demand curves can be calculated.

• Equations for the curves allow quantitative market analysis and prediction of effects from changes in market conditions.

Example: Using market data, economists estimate $a$, $b$, $c$, and $d$ in $Q_d = a - bP$ and $Q_s = c + dP$.

Effects of Government Intervention: Price Controls

Price Ceilings and Floors

• Price controls are government-imposed limits on prices (ceilings or floors).

• A price ceiling (maximum price) set below equilibrium creates a shortage (quantity demanded exceeds quantity supplied).

• A price floor (minimum price) set above equilibrium creates a surplus (quantity supplied exceeds quantity demanded).

Example: Rent control laws set a maximum price for apartments, often resulting in shortages.

Summary Table: Types of Elasticity

Type of Elasticity	Definition	Formula	Example
Price Elasticity of Demand	Responsiveness of quantity demanded to price change	$E_p = \frac{\Delta Q}{Q} / \frac{\Delta P}{P}$	Gasoline demand
Income Elasticity of Demand	Responsiveness of quantity demanded to income change	$E_I = \frac{\Delta Q}{Q} / \frac{\Delta I}{I}$	Luxury goods
Cross-Price Elasticity of Demand	Responsiveness of quantity demanded of one good to price change of another	$E_{xy} = \frac{\Delta Q_x}{Q_x} / \frac{\Delta P_y}{P_y}$	Tea and coffee
Price Elasticity of Supply	Responsiveness of quantity supplied to price change	$E_s = \frac{\Delta Q_s}{Q_s} / \frac{\Delta P}{P}$	Manufactured goods

Additional info: Some definitions and examples have been expanded for clarity and completeness. Mathematical notation and table formatting have been inferred and standardized for academic quality.