Price Elasticity of Demand (PED)
- The law of demand states that when there is an increase in price, there will be a fall in quantity demanded
- Economists are interested by how much the quantity demanded will fall
- Price elasticity of demand reveals how responsive the change in quantity demanded is to a change in price
- The responsiveness is different for different types of products
- The responsiveness is different for different types of products
Calculation of PED
- PED can be calculated using the following formula
- To calculate a % change, use the following formula
Worked example
A firm raises the price of its products from £10 to £15. Its sales fall from 100 to 40 units per day. Calculate the PED of its products
Step 1: Calculate the % change in QD
Step 2: Calculate the % change in P
Step 3: Insert the above values in the PED formula
The PED value will always be negative so economists ignore the sign and present the answer as 1.2
Interpreting PED Values
The Size of PED Varies From 0 To Infinity (∞) & Is Classified As Follows
Value | Name | Explanation |
0 | Perfectly Inelastic | The QD is completely unresponsive to a change in P (very theoretical value e.g. heart transplant is extremely inelastic but possibly not perfectly) |
0→1 | Relatively Inelastic | The %∆ in QD is less than proportional to the %∆ in P (e.g. addictive products) |
1 | Unitary Elasticity | The %∆ in QD is exactly equal to the %∆ in P |
1→ ∞ | Relatively Elastic | The %∆ in QD is more than proportional to the %∆ in P (e.g. luxury products) |
∞ | Perfectly Elastic | The %∆ in QD will fall to zero with any %∆ in P (highly theoretical elasticity) |
Factors That Influence the PED
- Some products are more responsive to changes in prices than other products
- The factors that determine the responsiveness are called the determinants of PED and include:
- Availability of substitutes: good availability of substitutes results in a higher value of PED (relatively elastic)
- Addictiveness of the product: addictiveness turns products into necessities resulting in a low value of PED (relatively inelastic)
- Price of product as a proportion of income: the lower the proportion of income the price represents, the lower the PED value will be. Consumers are less responsive to price changes on cheap products (relatively inelastic)
- Time period: In the short term, consumers are less responsive to price increases resulting in a low value of PED (relatively inelastic). Over a longer time period consumers may feel the price increase more and will then look for substitutes resulting in a higher value of PED (relatively elastic)