Lesson 3.1: Price Elasticity of Demand

Introduction

Welcome to Lesson 3.1 of Foundation Economics! In this lesson, we will explore one of the most critical concepts in economics: Price Elasticity of Demand (PED). By the end of this lesson, you will be able to define PED, calculate it using a formula, and interpret its values. You will also learn why PED is always negative and how to use it in real-world scenarios like business pricing and government taxation. So, let’s dive in!

Learning Objectives

After completing this lesson, you should be able to:

• Define price elasticity of demand (PED) and use the formula involving percentage changes.
• Interpret different PED values: elastic, inelastic, unit-elastic, perfectly elastic, and perfectly inelastic demand.
• Understand why PED is reported as a negative number and the importance of absolute values.
• Identify the determinants of PED: substitutes, necessity, proportion of income, time, and addiction/habit.
• Read PED from the shape and position of a demand curve.

Understanding Price Elasticity of Demand

Price Elasticity of Demand measures how the quantity demanded of a good responds to a change in its price. It is calculated using the following formula:

$$

PED = \frac{\% \text{ Change in Quantity Demanded}}{\% \text{ Change in Price}}

$$

This formula helps us understand the relationship between price changes and consumer purchasing behavior.

Interpreting PED Values

To understand the implications of PED, let’s examine what the values mean:

• Elastic Demand (PED > 1): A small increase in price leads to a large decrease in quantity demanded. For example, if the price of a luxury good like designer shoes increases, many consumers might choose to buy regular shoes instead.
• Inelastic Demand (PED < 1): A change in price results in a minor change in quantity demanded. For instance, if the price of essential goods like bread rises, most people will continue to buy it since they need it.
• Unit Elastic Demand (PED = 1): The percentage change in quantity demanded equals the percentage change in price. A good example is when a coffee shop raises the price of a coffee by 10%, and consumers reduce their purchase by 10%.
• Perfectly Elastic Demand (PED = ∞): Consumers will only buy the product at a specific price; any increase in price causes the quantity demanded to drop to zero (e.g., a product with perfect substitutes).
• Perfectly Inelastic Demand (PED = 0): Consumers buy the same quantity regardless of price changes (e.g., life-saving medications).

Why is PED Negative?

In economics, the law of demand states that as prices fall, quantity demanded rises, and vice versa. This inverse relationship results in a negative sign for PED. However, economists often report its absolute value, focusing on the magnitude rather than the sign. Thus, a PED of -2 would be interpreted simply as 2, indicating elastic demand.

Determinants of Price Elasticity of Demand

Now that we've covered the basics of PED, let’s discuss the factors that influence it:

1. Substitutes: The more substitutes available, the more elastic the demand. If the price of one brand of soda increases, consumers can easily switch to another brand.
2. Necessity vs. Luxury: Necessities tend to have inelastic demand because people need them (like food), while luxury items are often elastic since consumers can forgo them during price increases.
3. Proportion of Income: If a product is a large part of a consumer's budget (like rent), demand tends to be more elastic. Conversely, for inexpensive items (like gum), demand is usually inelastic.
4. Time: Over time, consumers can adjust their behavior. Short-term changes might show inelastic demand, but long-term adjustments can lead to more elastic responses as consumers find alternatives.
5. Addiction or Habit: For addictive goods (like cigarettes), demand is typically inelastic because consumers may continue purchasing despite price increases.

Reading PED from Demand Curves

PED can also be assessed graphically using a demand curve.

• A steep (inelastic) demand curve indicates that quantity demanded does not change significantly with price changes.
• A flat (elastic) demand curve shows that quantity demanded is highly responsive to price changes.

Example of Demand Curves

Imagine we have two products:

• Product A, with a steep demand curve, represents a necessity like gasoline.
• Product B, with a flatter demand curve, represents a luxury like smartphones. Changes in the price of gasoline lead to small changes in quantity demanded, while changes in smartphone prices lead to significant shifts in purchases.

Conclusion

Price elasticity of demand is not just a theoretical concept; it has real-world applications for businesses and governments. Understanding how demand changes with price can help set pricing strategies and tax policies.

By mastering PED, you become equipped to analyze market dynamics effectively and foresee how changes in prices might affect consumer behavior.

Study Notes

• Price Elasticity of Demand (PED) measures how quantity demanded responds to price changes using the formula:

$$

PED = \frac{\% \text{ Change in Quantity Demanded}}{\% \text{ Change in Price}}

$$

• PED Values:
• Elastic: PED > 1
• Inelastic: PED < 1

$ - Unit Elastic: PED = 1$

$ - Perfectly Elastic: PED = ∞$

• Perfectly Inelastic: PED = 0
• PED is always negative due to the law of demand; use the absolute value for practical purposes.
• Key determinants of PED include substitutes, necessity vs. luxury, proportion of income, time, and addiction/habit.
• Demand curves help visualize PED: steep for inelastic, flat for elastic.