IB Economics Income Elasticity of Demand (YED)

From Aldi to LVMH: What Your Shopping Trolley Tells Economists

Target Question:

What is income elasticity of demand and how do you calculate YED in IB Economics?

Let's go back to 2022 for a sec. A family in Manchester has been doing their weekly shop at Waitrose for years - the good biscuits, the fancy olive oil, the sourdough that costs more than a bus fare. Then the energy bills hit. Then the mortgage rate jumped. Real incomes - that's income adjusted for inflation - started falling. And quietly, without much fuss, the family started doing their big shop at Aldi instead.

Just… a change in behaviour that told economists everything they needed to know about the state of the economy.

That shift - from premium retailer to budget supermarket - is one of the most obvious real-world demonstrations of Income Elasticity of Demand (YED). And once you understand what it is, you'll start seeing it everywhere: in your own spending habits, in the news, in your IB Economics exam questions.

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IB Economics What is YED, and Why Is it Relevant?

Income Elasticity of Demand (YED) measures how the quantity demanded of a good changes in response to a change in consumers' real income.

So, YED measures how much the quantity demanded of a good changes when people's real income changes. "Real income" just means your income after accounting for inflation - how much stuff you can actually buy, not just the number on your payslip.

YED may be understood as the economy's mood thermometer. When YED values shift, they're essentially telling you: "Here's what people are buying more of - and what they're quietly abandoning."

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IB Economics The YED Formula (Very basic maths)

If your income goes up by 10% and you suddenly buy 20% more restaurant meals, the YED for restaurant meals is 2.0. If your income drops by 5% and your bread consumption barely budges, the YED for bread is pretty close to zero. The number tells you how sensitive demand is to changes in income.

IB Economics Real-life Examples:

Research suggests that grocery spending has a YED of around 0.5 on average - steady and reliable. Restaurant dining sits closer to 0.8. Fine dining? Around 2.4. That means a 10% income boost leads to a 24% jump in fancy restaurant visits.

Boom times = packed restaurants with wine pairings. Recession = everyone's making pasta at home again.

The Four Types of Goods (Compulsory Learning)

YED doesn't just give you a number - it tells you what type of good you're dealing with. There are four categories, and they behave very differently when incomes change.

Necessities: Boring (But Brilliant)

Let's be honest - necessities are not exactly rock and roll. Basic food, electricity, water, household gas. People buy roughly the same amount whether times are good or tight. You're not going to consume twice as much tap water just because you got a promotion.

A necessity has a YED between 0 and 1. Demand rises with income, but less than proportionately - consumers do not dramatically increase consumption of essential goods when they earn more.

But necessities are brilliant from a business perspective: they're recession-proof. Supermarkets' own-brand pasta? Electricity suppliers? These companies sleep well at night during a downturn because their customers have nowhere else to go.

IB Economics Exam Tip:

For necessities, the key phrase is "income inelastic demand." The percentage change in quantity demanded is smaller than the percentage change in income. YED is positive but less than 1.

Classic exam examples: basic food items, utilities, medical services.

Luxuries: When Money Burns a Hole in Your Pocket

When incomes rise, demand for luxury goods explodes. When incomes fall, they're the first thing cut from the budget.

A luxury good has a YED greater than 1, meaning demand rises more than proportionately when real income increases. Consumers significantly adjust spending on luxury goods in response to income changes.

IB Economics Real-life example: LVMH - the French conglomerate behind Louis Vuitton, Dior, Moët & Chandon and about 75 other brands you've definitely seen on Instagram. The global luxury goods market was valued at $327.52 billion in 2024 and is projected to reach $480 billion by 2033. A big chunk of that growth is being driven by rising real incomes in Asia, particularly China and India - exactly what YED would predict.

But it cuts both ways. In 2024, the luxury goods market actually dipped, with watches, leather goods, and shoes seeing a slowdown as consumers became more selective about purchases. Real incomes had been squeezed by inflation across Europe and the US. The YED story playing out in real time, right there in LVMH's quarterly reports.

LVMH also signed a massive 10-year deal with Formula One, with TAG Heuer replacing Rolex as the official F1 timekeeper. That's a luxury brand betting big on income growth returning - and using sport to reach aspirational consumers globally. Very YED-aware of them.

"Imagine you've just landed your first job after uni. Suddenly you've got a salary. Your spending doesn't scale up uniformly - you're not buying 40% more bread. Instead, you book a holiday abroad for the first time. You upgrade your phone. You start eyeing trainers that cost three figures. The luxuries jump. The necessities barely move. That's YED doing its job."

Inferior Goods: The Aldi Effect

A lot of my students have issues with the following notion - because the name is deeply misleading. Inferior goods are not necessarily bad quality goods. The word "inferior" in economics means something very specific: goods whose demand falls when income rises, because people switch to what they see as a better alternative.

An inferior good is one whose demand falls as real income rises, because consumers switch to higher-quality alternatives. Inferior goods have a negative YED.

Which brings us back to that Manchester family. During the UK's cost-of-living crisis, when real incomes were being hammered by inflation and energy bills, discount supermarkets like Aldi and Lidl gained significant market share as households traded down from premium retailers. Aldi overtook Morrisons in 2023 to become the UK's 4th largest supermarket. That's the inferior goods effect - not because Aldi's food is bad (it isn't), but because it represents a trade-down relative to what people were spending before.

As real incomes recover, some of those customers will drift back to Waitrose, Marks & Spencer Food, or at least the premium own-brand ranges. The demand curve for budget supermarkets shifts back outward. Aldi's sales were actually down in 2024 - partly because real incomes started stabilising. The YED pendulum swings both ways.

Other IB Economics real-life inferior goods examples:

Public transport vs. owning a car - as incomes rise, people switch to driving. Demand for buses and trains falls (relatively speaking).
Vinted and second-hand clothing - thriving during the cost-of-living crunch, starting to level off as finances improve.
Instant noodles vs. fresh food - classic staple that booms in hard times and fades when wages improve.

An inferior good is not the same as a low-quality good. A Mazda or a Renault is an inferior good relative to a BMW or Audi. It's still a perfectly decent car. "Inferior" just means people trade up when income allows. Mazda even makes its own supercar (the Mazda Furai) - very much not inferior in quality.

A Mix-Up That Costs Students Marks: YED vs PED

Right, this one's important. Every year, IB Economics students lose marks in exams by confusing YED and PED. Here's the classic error:

"Demand is income elastic because consumers buy more when prices fall."

Nope. That's PED territory. A price drop does create what economists call an income effect - you effectively feel richer because the price fell - but YED specifically and exclusively measures how demand responds to changes in actual income levels, not price changes. Keep them separate. They're different questions entirely.

IB Economics Exam Tip

PED = How does demand respond to a change in the good's price?
YED = How does demand respond to a change in consumers' real income?
Different variable. Different elasticity. Don't mix them up.

Engel Curves: Drawing the Story

Ernst Engel was a 19th-century German statistician who noticed patterns in how households spent money as their incomes changed. His name now lives on in IB Economics diagrams - the Engel curve.

Engel curves illustrate the relationship between real income and quantity demanded. Normal goods show a positive slope; inferior goods show a negative slope; luxury goods show a steeper positive slope than necessities.

An Engel curve plots real income on the vertical axis and quantity demanded on the horizontal axis. The slope of the curve tells you everything about the type of good:

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In exam diagram terms: an income rise from Y1 to Y2 causes a greater-than-proportionate rise in QD for luxuries (from Q1 to Q2), a smaller-than-proportionate rise for necessities, and a fall in QD for inferior goods. Your diagram should show all three curves clearly labelled - it's one of the most reliable diagram marks going.

Classifying Goods - It's Not Always Black and White

Here's where your IB Economics examiner wants to see critical thinking rather than robotic labelling. Some goods are genuinely hard to classify, and that's the point.

Take economy class flights. Relative to taking a bus or staying home, they seem like a luxury - they still take up a decent chunk of the average person's income. But compare them to business class or first class, and suddenly economy is the inferior option. Context matters.

Or consider laptops. In the UK, a laptop is largely a necessity - you need one for school, work, life. In many lower-income countries, a laptop is still very much a luxury good. Same product, different YED classification depending on where you are in the world.

The lesson? Don't just reach for the nearest label. Apply sound reasoning. IB Economics examiners love the phrase "it depends on the context" - as long as you follow it up with actual analysis and justify it properly.

Why YED Matters: Firms & Governments HL

YED and its relationship with the business cycle connects HL content about recessions and luxury goods to macroeconomics

For Higher Level students, you need to go beyond the definitions and think about why any of this matters to the real world. I can tell you it matters a lot.

For Businesses

Market Segmentation. Understanding YED allows companies to target different income groups with different product ranges. Think of how car manufacturers simultaneously sell a budget hatchback and a luxury SUV - they're deliberately covering both ends of the YED spectrum.

Pricing Strategy. Luxury brands actually raise prices during economic booms. When they expect rising incomes - especially in growing markets like China or India - they know demand will grow more than proportionately. LVMH doesn't discount. It leans in.

Diversifying Risk. Savvy conglomerates deliberately spread across the YED spectrum. Having both premium lines and budget options means you're hedged against the business cycle. When incomes fall, your premium range suffers, but your value range benefits. Pure portfolio management, informed by YED.

YED Sector Snapshot

Primary sector (oil, agriculture): Low YED - essential inputs regardless of economic conditions, so demand is relatively stable through the business cycle.

Secondary sector (manufacturing): Higher YED - more substitutes available, so demand responds more to income changes.

Tertiary sector (services): Highest YED - during a recession, services are typically the first budget casualty. Gym memberships, restaurant meals, leisure activities. They're the first to go when belts tighten.

For Governments

Taxation Policy. If a government wants to raise revenue without hitting ordinary people too hard, taxing luxury goods makes strategic sense. High YED goods are consumed mostly by higher-income households, so the tax burden is more progressive. This is literally why some governments impose specific luxury taxes on yachts, private jets, and high-end cars.

Welfare Programmes. Identifying inferior goods helps policymakers design better safety nets. If low-income households primarily consume inferior goods, targeted support programmes can be designed to improve access to higher-quality alternatives. It's not just economic theory - it's the blueprint for things like food voucher schemes and housing subsidies.

Economic Planning. If the government forecasts that real incomes will rise by 5% next year, and it knows the YED for various sectors, it can estimate how demand will shift across the economy. That informs everything from infrastructure investment to healthcare planning.

IB Economics Summary

YED essentially describes a picture of human priorities. What people buy more of when they have money - and what they quietly drop when they don't - tells you everything about what they value, what they consider essential, and where they aspire to be.

When Aldi's market share spikes in the UK, an economist reads that as a signal: real incomes are under pressure. When LVMH posts record profits and Formula One extends its sponsorship deal for a billion dollars, the reading is different: somewhere, a lot of people just got richer.

Every shopping trolley, every discarded Netflix subscription, every Ferrari test drive - they're all data points in the world's most honest survey. Your spending habits don't lie. Economists are just listening.

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Frequently Asked Questions: Income Elasticity of Demand (YED)

What is income elasticity of demand (YED) in IB Economics?

Income elasticity of demand (YED) measures how the quantity demanded of a good changes in response to a change in consumers' real income. It is calculated by dividing the percentage change in quantity demanded by the percentage change in real income. A positive YED indicates a normal good; a negative YED indicates an inferior good.

What is the difference between a luxury good and a necessity in economics?

A luxury good has a YED greater than 1 - demand rises more than proportionately when income increases. A necessity has a YED between 0 and 1 - demand rises with income, but only slightly. Examples of luxuries include designer goods and exotic holidays; examples of necessities include bread, milk, and household utilities.

Why do inferior goods have a negative YED?

Inferior goods have a negative YED because demand for them falls as real income rises - consumers switch to higher-quality alternatives when they can afford to. For example, as incomes rise, people tend to switch from discount supermarkets to premium retailers, from instant noodles to fresh food, and from public transport to owning a car.

What does an Engel curve show in economics?

An Engel curve shows the relationship between a consumer's real income and the quantity demanded of a good. Normal goods (including luxuries and necessities) show a positive slope - demand rises with income. Inferior goods show a negative slope - demand falls as income rises. Engel curves are a key diagram in the IB Economics elasticity topic.

How is YED useful for businesses and governments?

Businesses use YED to forecast how demand will change during economic booms or recessions, inform pricing strategies, and decide which product lines to develop. Governments use YED to design tax policy (taxing luxury goods raises revenue with minimal impact on essentials), build welfare programmes, and plan for economic shifts across different sectors of the economy.

Stay well,

Related Topics:

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IB Economics Microeconomics Hub Page access Income Elasticity of Demand (YED) content as well as the rest of module 2

IB Economics Diagrams Page Check Unit 9 for All Income Elasticity of Demand (YED) diagrams with explanations

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IB Economics Activity book Page Module 2 Microeconomics Unit 2.5 for Income Elasticity of Demand (YED) exam practice, activities, model answers and IB Economics Marking schemes

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