Understanding Income Elasticity of Demand and Goods Classification

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

\(E_I = \frac{\text{\% Change in Quantity Demanded}}{\text{\% Change in Income}}\)

Based on the value of income elasticity (\(E_I\)), goods can be classified into different types. Let's examine the types of goods listed and their typical income elasticity ranges:

• Inferior goods: These are goods for which demand decreases as consumer income increases. Their income elasticity of demand is negative (\(E_I < 0\)). Consumers tend to buy less of these goods when they can afford better alternatives.
• Giffen goods: A special type of inferior good, Giffen goods are very rare. For these goods, demand increases as the price increases, which is a violation of the law of demand. This occurs when the negative income effect (buying less because income effectively decreases) is stronger than the substitution effect (buying less because it's relatively more expensive). Giffen goods have negative income elasticity (\(E_I < 0\)), and the income effect is significant. Typically, Giffen goods are considered to have a more negative income elasticity than typical inferior goods.
• Necessities: These are goods considered essential for basic living (e.g., food, housing, utilities up to a basic level). Demand for necessities increases as income rises, but the increase is less than proportional to the rise in income. Their income elasticity of demand is positive but less than 1 (\(0 \leq E_I < 1\)).
• Normal goods: This is a broad category that includes any good for which demand increases as consumer income increases. Thus, normal goods have positive income elasticity of demand (\(E_I > 0\)). This category encompasses both necessities and luxuries. However, when listed alongside necessities and luxuries, "normal goods" often refers to goods with positive elasticity that are not strictly necessities or luxuries, perhaps with elasticity around 1. Based on the order provided in the correct option, "Normal goods" here seems to represent goods with income elasticity greater than necessities but less than luxuries.
• Luxury goods: These are non-essential goods or services that consumers buy more of as their income increases significantly. Demand for luxury goods increases more than proportionally to the rise in income. Their income elasticity of demand is positive and greater than 1 (\(E_I > 1\)).

We can summarize the typical income elasticity values for these goods in a table:

Arranging Goods by Ascending Income Elasticity

To arrange the goods in ascending order of their underlying income elasticity of demand, we need to order them from the lowest (most negative) elasticity to the highest (most positive) elasticity.

Comparing the elasticity ranges:

• Giffen goods have negative elasticity, potentially the lowest among the listed types.
• Inferior goods also have negative elasticity, but typically higher (less negative) than Giffen goods.
• Necessities have elasticity between 0 and 1.
• Normal goods (in the context of this question) have positive elasticity, positioned between necessities and luxuries.
• Luxury goods have elasticity greater than 1, the highest among the types listed.

Therefore, the ascending order of income elasticity is:

1. Giffen goods (E): Most negative \(E_I\)
2. Inferior goods (B): Negative \(E_I\), but greater than Giffen goods
3. Necessities (A): \(0 \leq E_I < 1\)
4. Normal goods (C): \(E_I > 0\), likely \(E_I(\text{A}) < E_I(\text{C}) < E_I(\text{D})\)
5. Luxury goods (D): \(E_I > 1\)

The ascending order of the goods based on their income elasticity of demand is (E), (B), (A), (C), (D).

Revision Table: Income Elasticity Overview

Additional Information on Demand Elasticity

Income elasticity of demand is just one type of elasticity used in economics. Other important elasticities include:

• Price Elasticity of Demand: Measures the responsiveness of the quantity demanded of a good to a change in its price. It helps determine if a good is elastic (quantity demanded is highly responsive to price changes, \(|E_p| > 1\)) or inelastic (quantity demanded is not very responsive, \(|E_p| < 1\)). Unitary elasticity means \(|E_p| = 1\).
• Cross-Price Elasticity of Demand: Measures the responsiveness of the quantity demanded for one good to a change in the price of another good. It is used to determine if two goods are substitutes (positive cross-price elasticity) or complements (negative cross-price elasticity). If the cross-price elasticity is zero, the goods are unrelated.

Understanding different types of elasticity is crucial for businesses for pricing decisions, forecasting demand, and understanding market dynamics. For governments, elasticity analysis helps in predicting the effects of taxes and subsidies.