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Chapter 5: Income Elasticity of Demand (YED)

Part 5.1 – Understanding Income Elasticity of Demand

By Dr. Anthony Fok

Introduction

Imagine Singapore’s economy grows by 5% next year.

Workers receive higher salaries.

Bonuses increase.

Consumer confidence improves.

How will households spend their additional income?

Will they buy more groceries?

Will they travel overseas more frequently?

Will they upgrade their mobile phones?

Will demand for luxury handbags increase faster than demand for rice?

Economists use Income Elasticity of Demand (YED) to answer these questions.

Unlike Price Elasticity of Demand, which examines how demand changes when prices change, Income Elasticity of Demand studies how demand changes when consumer income changes.

This concept is extremely useful because income changes continuously throughout the business cycle.

During periods of economic growth, household incomes usually increase.

During recessions, incomes may stagnate or decline.

Businesses, investors and governments therefore use YED extensively to forecast consumer demand and make strategic decisions.

What Is Income Elasticity of Demand?

Income Elasticity of Demand measures the responsiveness of quantity demanded to a change in consumer income, assuming all other factors remain constant.

The formula is:

Income Elasticity of Demand (YED) = Percentage Change in Quantity Demanded ÷ Percentage Change in Income

Unlike Price Elasticity of Demand, YED can be:

  • positive,
  • negative,
  • zero.

The sign itself carries important economic meaning.

Why Is YED Important?

Understanding YED enables firms to predict how demand changes as economies expand or contract.

Retailers use YED when deciding:

  • product ranges,
  • inventory levels,
  • expansion plans,
  • pricing strategies.

Governments use YED to forecast:

  • consumer spending,
  • tax revenue,
  • economic growth,
  • changes in living standards.

Investors also analyse YED when deciding which industries are likely to perform well during different phases of the economic cycle.

Positive Income Elasticity of Demand

When YED is positive:

Demand increases as income increases.

These products are known as normal goods.

Most goods and services fall into this category.

Examples include:

  • restaurant meals,
  • holidays,
  • smartphones,
  • household appliances,
  • education services.

As consumers become wealthier, they generally purchase more of these goods.

What Are Normal Goods?

A normal good is one for which demand increases when consumer income rises.

For example:

A university graduate receives a substantial salary increase.

She may decide to:

  • dine at restaurants more frequently,
  • travel overseas,
  • purchase a higher-quality laptop,
  • enrol in professional development courses.

Demand for these products increases because higher income enables greater spending.

Categories of Normal Goods

Not all normal goods respond equally to income changes.

Economists distinguish between:

  • necessities,
  • luxury goods.

This distinction is based on the numerical value of YED.

Necessities

Necessities have:

Positive YED less than 1

Examples include:

  • rice,
  • bread,
  • electricity,
  • public transport,
  • basic clothing.

Although consumers buy slightly more when income rises, demand increases proportionately less than income.

For example:

Income increases by 20%.

Demand for rice increases by only 5%.

Rice remains important, but consumers cannot eat unlimited quantities simply because they earn more.

Luxury Goods

Luxury goods have:

YED greater than 1

Demand increases proportionately more than income.

Examples include:

  • luxury cars,
  • premium watches,
  • overseas holidays,
  • designer fashion,
  • high-end electronics.

Suppose household income rises by 10%.

Demand for luxury holidays may increase by 25%.

This indicates a high positive income elasticity of demand.

Luxury goods benefit disproportionately during periods of strong economic growth.

Negative Income Elasticity of Demand

When YED is negative:

Demand decreases as income increases.

These products are known as inferior goods.

The term “inferior” does not mean low quality.

Instead, it describes consumer behaviour.

As incomes increase, consumers switch to preferred alternatives.

Examples of Inferior Goods

Possible examples include:

  • lower-priced instant noodles,
  • generic supermarket brands,
  • second-hand clothing in certain markets,
  • basic transport options where consumers later upgrade.

As consumers become wealthier, they often substitute these products with higher-quality alternatives.

Singapore Example

A young graduate begins his career with a modest salary.

Initially, he relies primarily on buses and MRT services.

Several years later, after receiving promotions and salary increases, he purchases a private car.

Demand for private transport rises.

Demand for some lower-cost transport options may grow more slowly or even decline for that individual.

This illustrates how changing income influences consumption patterns.

YED Throughout the Business Cycle

Income Elasticity of Demand becomes particularly important during different phases of the economy.

During Economic Expansion

When incomes rise:

  • demand for luxury goods increases rapidly,
  • tourism expands,
  • restaurant spending increases,
  • entertainment industries perform well,
  • premium retail sales often strengthen.

Businesses producing luxury products generally benefit most.

During Economic Recession

When incomes fall:

  • luxury spending declines,
  • consumers postpone major purchases,
  • demand shifts towards lower-cost alternatives,
  • discount retailers may experience stronger sales.

Understanding YED helps firms prepare for changing economic conditions.

Dr. Anthony Fok’s Exam Tip

Students often memorise:

Positive YED = Normal Goods.

Negative YED = Inferior Goods.

This is only the starting point.

In examinations, always explain why consumers change their purchasing behaviour as income changes.

Economic reasoning—not memorisation—earns the highest marks.

Common Student Mistake

❌ “Inferior goods are poor-quality goods.”

Incorrect.

An inferior good is defined by consumer behaviour, not product quality.

A product is inferior if demand falls when income rises.

Some products that are perfectly acceptable in quality may still be classified as inferior because consumers switch to more preferred alternatives as their incomes increase.

Quick Revision Summary

You should now be able to:

  • Define Income Elasticity of Demand.
  • Calculate YED.
  • Distinguish between positive and negative YED.
  • Explain the difference between normal goods and inferior goods.
  • Differentiate necessities from luxury goods.
  • Apply YED to changes in the business cycle.
  • Use Singapore examples to support economic analysis.

These concepts provide the foundation for understanding how income growth influences consumer spending and business performance.

Coming Up in Part 5.2

In the next section, we will explore:

  • Determinants of Income Elasticity of Demand.
  • Why some products are luxuries while others are necessities.
  • Business applications of YED.
  • Forecasting demand during economic growth and recession.
  • Singapore case studies.
  • Cambridge examination techniques.