1. Interpreting Price Elasticity of Demand and other Elasticities

2. Clarifying Price Elasticities
Perfectly inelastic
When quantity demanded does not respond at all to changes in price
Demand curve is a vertical line
Price elasticity equals 0

3. Perfectly elastic
When any price increase will cause the quantity demanded to drop to zero.
Demand curve is horizontal
This implies an infinite price elasticity of demand

4. Elastic Inelastic Unit elastic
Price elasticity of demand is greater than 1
Inelastic
Price elasticity of demand is less than 1
Unit elastic
Price elasticity of demand is exactly 1

5. Why does it matter whether demand is elastic, inelastic or unit elastic?
It helps predict how changes in price will affect total revenue, earned by producers from the sale of that good.
Total Revenue = P X Q

6. Also two countervailing effects are present
A price effect
After a price increase, each unit sold sells at a higher price, which tends to raise revenue
A quantity effect
After a price increase, fewer units are sold, which tends to lower revenue

7. What factors determine Price Elasticity of Demand?
Whether close substitutes are available
Price elasticity of demand tends to be high if there are other goods that consumers regard as similar and would be willing to consume instead
Price elasticity of demand tends to be low if there are no close substitutes

8. Whether a good is a necessity or a luxury?
Price elasticity tends to be low if it is something you must have
Price elasticity tends to be high if the good is a luxury

9. Share of income spent on the good
Price elasticity of demand tends to be low when spending on a good accounts for a small share of a consumer’s income
A significant change in price has little impact on how much a consumer spends
When the good accounts for a significant share of consumer spending, consumer is less likely to be responsive to a change in price thus price elasticity of demand is high

10. Time
Price elasticity of demand tends to increase as consumers have more time to adjust to a price change
Long-run price elasticity of demand is higher than short-run elasticity.

11. Other Elasticities Cross-Price Elasticity of Demand
Demand for a good is often affected by the prices on other goods (substitutes and complements)
A change in the price of related good shifts the demand curve of the original good, reflecting a change in the quantity demanded at any given price.

12. This can be measured by the cross-price elasticity of demand
It is a ratio of the percent change in the quantity demanded of one good to the percent change in the price of another.

13. If two goods are substitutes (i. e
If two goods are substitutes (i.e. hot dogs/ hamburgers) cross-price elasticity of demand is positive
If they are close substitutes cross-price elasticity will be positive and large
If not cross-price elasticity will be positive and small

14. When two goods are complements (i. e
When two goods are complements (i.e. hot dogs/ hot dog buns) cross-price elasticity is negative
If the cross-price elasticity is slightly below zero, they are weak complements, if it is very negative, they are strong complements
In the case of cross price elasticity the plus or minus sign is very important: it indicates whether the goods are substitutes or complements

15. Income Elasticity of Demand
Measures how changes in income affect the demand for a good
Income elasticity of demand can be both positive and negative
When the income elasticity of demand is positive, the good is a normal good- the quantity demanded at any given price increases as income increases
When it is negative, the good is an inferior good- quantity demanded at any given price decreases as income increases

16. Economist use income-elasticity of demand to predict which industries will grow most rapidly as incomes of consumers grow over time.
This helps make a useful distinctions among normal goods

17. Income elastic
The income elasticity of demand for that good is greater than 1
When income rises, the demand for income-elastic goods rise faster than income
Example: second homes and international travel

18. Income inelastic
The income elasticity of demand for that good is positive but less than 1
When income rises, demand for income-inelastic goods rises, but more slowly than income
Example: food and clothing

19. Price Elasticity of Supply
Definition: A measure of the responsiveness of the quantity of a good supplied to the price of that good. It is the ratio of the percent change in quantity supplied to the percent change in the price as we move along the supply curve.
Formula

20. Extreme Values Perfectly Inelastic Supply = 0
Graphed Vertically
Perfectly elastic Supply = infinite
Graphed horizontally

21. Factors that determine Price Elasticity of Supply
Availability of Inputs
Price elasticity of supply tends to be large when inputs are readily available and can be shifted into and out of production at a relatively low cost
Price elasticity of supply tends to be small when inputs are available only in a more-or-less fixed quantity or can be shifted into and out of production only at a relatively high cost

22. Time
Price elasticity of supply tends to grow larger as producers have more time to respond to a price change
Long-run price elasticity of supply is often higher than short run elasticity

23. Short run = a few weeks or months
Long run = several years