Understanding Income Elasticity for Inferior Goods

The question asks about the income elasticity of demand specifically for inferior goods. To answer this, we need to understand what inferior goods are and how their demand changes with respect to income, and then relate this to the concept of income elasticity of demand.

What are Inferior Goods?

Inferior goods are types of goods for which demand decreases as the income of the consumer increases. Conversely, as income decreases, the demand for inferior goods increases. This is because consumers tend to switch to more expensive, preferred alternatives when their income rises.

• Examples of inferior goods might include cheaper forms of transportation (like bus travel compared to owning a car), certain budget-brand foods, or second-hand clothing.

What is Income Elasticity of Demand?

Income elasticity of demand measures how sensitive the quantity demanded of a good is to a change in consumer income. It is calculated using the following formula:

$\text{Income Elasticity of Demand} = \frac{\% \text{ Change in Quantity Demanded}}{\% \text{ Change in Income}}$

The sign of the income elasticity tells us about the nature of the good:

• If income elasticity is positive, the good is a normal good (demand increases as income increases).
• If income elasticity is negative, the good is an inferior good (demand decreases as income increases).
• If income elasticity is zero, the good is a necessity whose demand doesn't change significantly with income.

Income Elasticity for Inferior Goods Explained

As established, for an inferior good, there is an inverse relationship between income and the quantity demanded. When income goes up (a positive percentage change), the quantity demanded goes down (a negative percentage change). When income goes down (a negative percentage change), the quantity demanded goes up (a positive percentage change).

Let's look at the formula again:

$\text{Income Elasticity} = \frac{\% \Delta \text{ Quantity Demanded}}{\% \Delta \text{ Income}}$

If income increases ($\% \Delta \text{ Income}$ is positive), the quantity demanded of an inferior good decreases ($\% \Delta \text{ Quantity Demanded}$ is negative). A negative number divided by a positive number results in a negative value.

If income decreases ($\% \Delta \text{ Income}$ is negative), the quantity demanded of an inferior good increases ($\% \Delta \text{ Quantity Demanded}$ is positive). A positive number divided by a negative number also results in a negative value.

Therefore, in the case of inferior goods, the income elasticity of demand is always negative.

Based on this analysis, the income elasticity of demand for inferior goods is negative.

Revision Table: Key Concepts

Additional Information: Giffen Goods

While inferior goods have negative income elasticity, there's a special case called Giffen goods. Giffen goods are extreme inferior goods where the negative income effect is so strong that it outweighs the positive substitution effect when the price changes. For a Giffen good, the demand curve slopes upward (violating the law of demand). However, all Giffen goods are inferior goods, but not all inferior goods are Giffen goods. The defining characteristic for inferior goods regarding income is that demand decreases when income increases, resulting in a negative income elasticity.