Income Elasticity of Demand: Comprehensive Study Guide

Income elasticity of demand measures the responsiveness of the quantity demanded for a product to a change in the income of consumers.
It is a critical factor for businesses to understand as household spending power directly influences purchasing behavior.

The formula used to calculate income elasticity of demand is: $\text{Income elasticity of demand} = \frac{\text{Percentage change in quantity demanded}}{\text{Percentage change in income}}$
Worked Example Product A: - Percentage change in income = $10\%$ - Percentage change in demand = $25\%$ - Calculation: $\frac{25\%}{10\%} = 2.5$ - Conclusion: The change in demand is proportionately greater than the change in income, making it income elastic.
Worked Example Product B: - Percentage change in income = $10\%$ - Percentage change in demand = $5\%$ - Calculation: $\frac{5\%}{10\%} = 0.5$ - Conclusion: The change in demand is proportionately less than the change in income, making it income inelastic.

Elasticity > 1: Demand is income elastic. The percentage change in demand is greater than the percentage change in income. Examples include cars, fashion accessories, entertainment, and luxury holidays.
Elasticity < 1: Demand is income inelastic. The percentage change in demand is less than the percentage change in income. Examples include basic necessities like milk, general food, and heating fuel.
Normal Goods: These are goods where an increase in income leads to an increase in demand. The income elasticity value is always positive ( $+$ ).
Inferior Goods: These are goods where an increase in income leads to a decrease in demand. The income elasticity value is always negative ( $-$ ).

Product W: Elasticity of $0.6$ (Inelastic, Normal). A $10\%$ income increase results in a $6\%$ demand increase.
Product X: Elasticity of $-2.4$ (Elastic, Inferior). A $10\%$ income increase results in a $24\%$ demand fall.
Product Y: Elasticity of $1.9$ (Elastic, Normal). A $10\%$ income increase results in a $19\%$ demand rise.
Product Z: Elasticity of $-0.8$ (Inelastic, Inferior). A $10\%$ income increase results in an $8\%$ demand fall.

Necessities vs. Luxuries: - Necessities: Basic goods (food, water, electricity) have income inelastic demand (< 1). - Luxuries: Discretionary goods (air travel, satellite TV, tourism) have income elastic demand (> 1). - Cigarettes: Can be considered a necessity due to addiction. A study in Ukraine found the income elasticity for cigarettes to be as low as $0.06$ .
Price Relative to Income: - Cheap items like pencils tend to be income inelastic. - Expensive items like houses tend to be income elastic.
Imported Goods: Demand for imports often rises significantly as developing nations become wealthier, suggesting high income elasticity.

Cyclical Demand: Businesses selling highly income-elastic goods (luxury goods, restaurants) face cyclical demand. They thrive during economic growth but suffer during recessions, often leading to layoffs and canceled investments.
Stability: Businesses selling income-inelastic goods (stable food products like bread) experience more stable demand throughout the business cycle, making production planning easier.
Production Planning: - If incomes are expected to rise, businesses with elastic demand plan to increase capacity. - During the 2008 recession, Honda (the Japanese car manufacturer) halted production at its UK Swindon factory for four months (February–May 2009) due to falling demand.
Inferior Goods Strategy: Producers of inferior goods (e.g., no-frills low-cost supermarkets) may actually build capacity during a recession as demand for their products increases when incomes fall.
Product Switching: Manufacturers with flexible resources may switch production lines based on income trends. For example, a plastic molder might switch from household goods to toys if income growth is predicted.

Background: A baker in the West Midlands that shifted its focus from bread ( $80\%$ of sales pre-2003) to fresh cream cakes. By 2008, cakes accounted for over $40\%$ of revenue.
Problem: During the 2008–2010 recession, cake sales fell sharply, causing layoffs and canceled machinery investments.
Data Points: - Income elasticity of demand for bread = $0.6$ (Normal/Inelastic). - Income elasticity of demand for cakes = $3.9$ (Normal/Highly Elastic).
Impact Analysis: If average income falls by $7\%$ , the demand for cakes would fall by $27.3\%$ (calculated as $3.9 \times -7\% = -27.3\%$ ). The UK GDP per capita graph (2004–2014) confirms a significant dip in average individual income during this period.

Maths Tip: Always include positive ( $+$ ) and negative ( $-$ ) signs in calculations to correctly identify if a good is normal or inferior.
Exam Tip: Do not confuse Income Elasticity with Price Elasticity of Demand. Both use percentage change in demand as the numerator, but the denominator for income elasticity is the percentage change in income, while for price elasticity, it is the percentage change in price.
Quantitative Exercise (Healy Ltd): In 2014, incomes rose by $2\%$ . Paper demand rose from $2,000,000$ to $2,030,000$ reams. - Percentage change in demand: $(\frac{30,000}{2,000,000}) \times 100 = 1.5\%$ - YED: $\frac{1.5}{2.0} = 0.75$ - Conclusion: Paper is a normal, income-inelastic good.