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Elasticities of Demand

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Elasticity

Elasticity measures the responsiveness of one variable to the change in another variable.

Price elasticity of demand (PED)

Price elasticity of demand (PED)

  • Price elasticity = % change in quantity demanded ÷ % change in price.
    • Elastic demand is where the PED > 1.
    • Inelastic demand is where the PED < 1.
    • Unitary elasticity is where the PED = 1.
  • PED is almost always negative as an increase in price would result in a decrease in demand. But you may see some questions refer to it as positive for ease.
Income elasticity of demand (YED)

Income elasticity of demand (YED)

  • Income elasticity of demand = % change in quantity demanded ÷ % change in income.
    • Normal goods have a positive income elasticity, YED > 0 (income rises; demand increases).
    • Inferior goods have negative income elasticity, YED < 0 (income rises; demand decreases).
  • For example, those with higher income may buy fewer burgers and more steaks. Burgers in this case are an inferior good.
  • YED can be positive or negative.
Cross-price elasticity of demand (XED)

Cross-price elasticity of demand (XED)

  • Cross-price elasticity of demand is when a change in the price of one good can change the quantity demanded of another.
  • Cross-price elasticity of demand = % change in quantity demanded of good A ÷ % change in the price of good B.
  • XED is positive if the goods are substitutes and negative if the goods are complements - you can work this out for yourself but also try to remember it!
  • If XED is close to zero this would suggest that the goods are unrelated.

Complement Goods vs Substitute Goods

The cross-price elasticity of demand (XED) for complements is negative because a fall in the price of one good will increase the quantity demanded for the other good.

Complement goods

Complement goods

  • For complements, a fall in the price of one good will lead to an increase in the quantity demanded for the other good. Complements have negative cross-price elasticities of demand.
    • E.g. peanut butter and bread.
    • E.g ice cream and sun cream.
    • XED < 0
Substitute goods

Substitute goods

  • For substitutes, a fall in the price of one will lead to a fall in the quantity demanded of the other. Substitutes have positive cross elasticities of demand.
    • E.g. coffee and tea.
    • XED > 0
Independent goods

Independent goods

  • Independent goods have a cross-price elasticity of demand of zero.
    • E.g donkeys and ice cream.
    • XED = 0
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A Global Perspective

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Examples of Global Policy

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