1. Chapter 6: Elasticity

2. Elasticity
A measure of the responsiveness of one variable (usually quantity demanded or supplied) to a change in another variable
Most commonly used elasticity: price elasticity of demand, defined as:
Price elasticity of demand =

3. Price elasticity of demand
Demand is said to be:
elastic when Ed > 1,
unit elastic when Ed = 1, and
inelastic when Ed < 1.

4. Perfectly elastic demand

5. Perfectly inelastic demand

6. Elasticity & slope
a price increase from $1 to $2 represents a 100% increase in price,
a price increase from $2 to $3 represents a 50% increase in price,
a price increase from $3 to $4 represents a 33% increase in price, and
a price increase from $10 to $11 represents a 10% increase in price.
Notice that, even though the price increases by $1 in each case, the percentage change in price becomes smaller when the starting value is larger.

7. Elasticity along a linear demand curve

8. Elasticity along a linear demand curve

9. Arc elasticity measure
where:

10. Example
Suppose that quantity demanded falls from 60 to 40 when the price rises from $3 to $5. The arc elasticity measure is given by:
In this interval, demand is inelastic (since elasticity < 1).

11. Elasticity and total revenue
Total revenue = price x quantity
What happens to total revenue if the price rises?
Price elasticity of demand =

12. Elasticity and TR (cont.)
Price elasticity of demand =
A reduction in price will lead to:
an increase in TR when demand is elastic.
a decrease in TR when demand is inelastic.
an unchanged level of total revenue when demand is unit elastic.

13. Elasticity and TR (cont.)
Price elasticity of demand =
In a similar manner, an increase in price will lead to:
a decrease in TR when demand is elastic.
an increase in TR when demand is inelastic.
an unchanged level of total revenue when demand is unit elastic.

14. Elasticity and TR (cont.)

15. Price discrimination
different customers are charged different prices for the same product, due to differences in price elasticity of demand
higher prices for those customers who have the most inelastic demand
lower prices for those customers who have a more elastic demand.

16. Price discrimination (cont.)
customers who are willing to pay the highest prices are charged a high price, and
customers who are more sensitive to price differentials are charged a low price.

17. Determinants of price elasticity
Price elasticity is relatively high when:
close substitutes are available,
the good or service is a large share of the consumer's budget, and
a longer time period is considered.

18. Cross-price elasticity of demand
The cross-price elasticity of demand between two goods j and k is defined as:

19. Cross-price elasticity (cont.)
cross-price elasticity is positive if and only if the goods are substitutes
cross-price elasticity is negative if and only if the goods are complements.

20. Income elasticity of demand
A good is a normal good if income elasticity > 0.
A good is an inferior good if income elasticity < 0.

21. Income elasticity of demand
A good is a luxury good if income elasticity > 1.
A good is a necessity good if income elasticity < 1.

22. Price elasticity of supply

23. Perfectly inelastic supply

24. Perfectly elastic supply

25. Determinants of supply elasticity
short run - period of time in which capital is fixed
all inputs are variable in the long run
supply will be more elastic in the long run than in the short run since firms can expand or contract their capital in the long run.

26. Tax incidence
distribution of the burden of a tax depends on the elasticities of demand and supply.
When supply is more elastic than demand, consumers bear a larger share of the tax burden.
Producers bear a larger share of the burden of a tax when demand is more elastic than supply.