In-Depth Notes on Demand and Elasticity

Demand and Price Dynamics
  • Downward Sloping Demand Line
    • Reason: Price falls, quantity demanded increases due to substitution effect (consumers switch to cheaper options) and income effect (real income increases as price decreases).
Elasticity of Demand
  • Own Price Elasticity of Demand: Measures responsiveness of quantity demanded to a change in its own price.
  • Elastic Demand: Occurs when elasticity coefficient $ε > 1$ (small price changes result in large quantity changes).
  • Inelastic Demand: Occurs when $ε < 1$ (large price changes result in little quantity change).
    • Examples:
    • Elastic: Luxury cars, restaurant meals.
    • Inelastic: Insulin, salt.
  • Comparing Demand Curves:
    • Flatter demand curves are more elastic (greater responsiveness to price changes).
Policy and Elasticity
  • Importance in Policy:
    • Predicts outcomes of taxes and subsidies on behavior and revenue.
  • Private Policy Example: Streaming services lowering prices to increase subscriptions if demand is elastic.
  • Public Policy Example: Cities taxing sugary drinks with expectation of reduced consumption due to elastic demand.
Types of Elasticity
  • Perfectly Elastic Demand: Horizontal line; consumers buy any amount at one price, none at higher prices.
  • Perfectly Inelastic Demand: Vertical line; consumers buy the same quantity regardless of price.
  • Seller Preference: Sellers prefer inelastic demand to increase prices without losing customers.
Factors Affecting Elasticity
  • Substitutes: More available substitutes increase elasticity (e.g., Coke vs. Pepsi).
  • Time: More time allows consumers to adjust and find alternatives, increasing elasticity.
  • Price relative to Income: Higher-priced goods are more elastic for low-income consumers.
  • Key Factors: Substitutes, time, necessity vs. luxury status, and price relative to income.
Elasticity Calculations
  • Own Price Elasticity Formula: ε = \frac{%ΔQ}{%ΔP}
  • Use of Absolute Value: Focuses on magnitude, not direction, since demand is usually negative.
  • Percentage Change: Allows elasticity to be independent of units (e.g., a $1 change for a pack of gum differs from a $1 change for a car).
Interpretation of Elasticity Values
  • $ε > 1$: Elastic demand.
  • $ε < 1$: Inelastic demand.
  • $ε = 1$: Unit elastic demand.
Elasticity and Total Revenue
  • Relationship:
    • Elastic: If price increases, total revenue decreases.
    • Inelastic: If price increases, total revenue increases.
  • Concept of "Charge More = Make More": Only valid if demand is inelastic.
Advertising and Competition
  • Impact of Advertising: Ads can help increase perceived product differentiation, particularly in elastic demand scenarios.
  • Firms in Perfect Competition: Face perfectly elastic demand due to the availability of substitutes.
Policy Implications of Elasticity
  • Example of Inelastic Demand: Higher drug prices may increase crime as demand remains stable.
  • Ineffective Policies: Heavy taxation on inelastic goods (e.g., cigarettes) could lead to black markets.
  • Tax Incidence: Depends on elasticity; the burden can either fall on buyers or sellers.
Cross-Price Elasticity and Market Dynamics
  • Cross-Price Elasticity Formula: \text{Cross-price elasticity} = \frac{% ΔQd \ of \ good \ X}{% ΔP \ of \ good \ Y}
  • Complements vs. Substitutes:
    • Complements: Consumed together (negative cross-price elasticity).
    • Substitutes: Used in place of each other (positive cross-price elasticity).
  • Interconnected Markets: Policy/actions on one market affect others; promoting holistic policy considerations is crucial.
Income Effects on Demand
  • Normal Goods: Demand increases as income increases (e.g., organic groceries).
  • Inferior Goods: Demand decreases as income increases (e.g., instant noodles).
  • Income Elasticity Equation: \text{Income elasticity} = \frac{%ΔQd}{%ΔIncome}
Market Demand
  • Market Demand vs. Individual Demand: Market demand is the horizontal sum of individual demand curves.
  • Shifting Demand Factors: Key factors include income, tastes, demographics, prices of related goods, expectations, and population changes.
Production and Cost
  • Marginal Cost (MC) Derivation: Based on marginal product; if input costs are constant, MC=wageMPMC = \frac{wage}{MP}.
  • MC Behavior: MC is at its lowest when marginal productivity is peak.
  • Upward-Sloping MC Curve: Represents the firm's supply under perfect competition.
Revenue Concepts
  • Total Revenue (TR): TR=P×QTR = P \times Q
  • Total Cost (TC): TC=fixed+variable costsTC = fixed + variable \ costs
  • Profit Analysis:
    • Profit: If TR > TC.
    • Loss: If TR < TC.
    • Break-even: If TR = TC.
Structural Changes in Supply
  • Impact of Entry/Exit: Entry increases supply and decreases prices; exit decreases supply and increases prices.