Define YED and calculate it using the correct formula
Classify goods as normal, luxury, necessity or inferior using YED values
Define XED and use its sign to identify substitutes and complements
Apply YED and XED to business strategy and recession planning
Income Elasticity of Demand
What is YED?
Key Formula
YED = % change in Qd ÷ % change in Income
Measures how sensitive demand for a good is to a change in consumer income. Unlike PED, YED can be positive or negative depending on the type of good.
POSITIVE YED
As income rises, demand rises. These are normal goods — the majority of goods and services.
NEGATIVE YED
As income rises, demand falls. These are inferior goods — consumers switch to better alternatives when they can afford to.
Income Elasticity of Demand
Classifying Goods by YED
YED < 0
Inferior Good
Demand falls as income rises. Consumers switch to better alternatives.
Examples: Aldi own-brand, bus travel, instant noodles
0 < YED < 1
Normal Necessity
Demand rises with income but less than proportionately.
Examples: food, electricity, clothing
YED > 1
Luxury Good
Demand rises more than proportionately with income.
Examples: Rolls-Royce, fine dining, designer goods
YED = 0
Income Inelastic
Demand completely unaffected by income changes.
Examples: salt, matches — very rare in practice
Real-World Application · YED
The 2008 Crash: Luxury vs Inferior Goods
🚗 ROLLS-ROYCE — HIGH POSITIVE YED
Global financial crisis hit in 2008. As incomes fell sharply, Rolls-Royce sales collapsed 45% in 2009. When recovery came 2010–11, sales rebounded even faster — YED ≈ +3.0 to +4.0. Luxury goods are highly income-sensitive — the ultimate high-YED product.
🛒 ALDI & LIDL — NEGATIVE YED (for premium rivals)
As incomes fell in 2008-09, UK shoppers switched from Tesco/Sainsbury's to Aldi and Lidl. Budget supermarket market share grew from 4% → 10%+ over the decade. Budget groceries are inferior substitutes — demand rises when incomes fall. YED for premium brands became negative as consumers downgraded.
📊 BUSINESS LESSON
Smart firms build diversified product portfolios across YED ranges. Unilever sells both luxury brands (Magnum, Dove) and budget staples (Persil, PG Tips) — recession hits luxury lines but budget lines hold or grow. This is income elasticity portfolio management.
Cross Elasticity of Demand
What is XED?
Key Formula
XED = % change in Qd of Good A ÷ % change in Price of Good B
Measures how demand for one good responds to a price change in another good. The sign (positive or negative) tells you the relationship between the goods.
XED > 0 (POSITIVE) → SUBSTITUTES
Price of B rises → demand for A rises. Consumers switch from B to A. Coke vs Pepsi, butter vs margarine.
XED < 0 (NEGATIVE) → COMPLEMENTS
Price of B rises → demand for A falls. Goods are used together. Petrol and cars, printers and ink cartridges.
XED = 0 → UNRELATED
No relationship. Price of B has no effect on demand for A. Bread and motorbikes.
Cross Elasticity of Demand
XED: Substitutes vs Complements
SUBSTITUTES (XED > 0)
D₁ = Original demand
D₂ = Demand after rival's price rises
COMPLEMENTS (XED < 0)
D₁ = Original demand
D₂ = Demand after complement's price rises
Real-World Application · XED
Sony & PlayStation: The Complement Trap
🎮 CONSOLE vs CONSOLE (SUBSTITUTES)
PlayStation 5 and Xbox Series X are substitutes — XED is positive. When Xbox raised Game Pass prices in 2023, PS5 subscriptions and console sales saw a measurable uptick as gamers reconsidered platforms.
🎯 CONSOLE vs GAMES (COMPLEMENTS)
Console and games are complements — XED is negative. Sony strategically prices PS5 consoles near cost because every console sold drives game, subscription, and DLC revenue. XED(console, game) ≈ −1.8.
🔒 EXCLUSIVES — WEAPONISING XED
Sony's exclusive titles (Spider-Man, God of War, Horizon) deepen the complement relationship — they increase the magnitude of the negative XED between PlayStation hardware and its software library. An exclusive makes your console-game pair unique and non-substitutable — raising switching costs and locking in customers. Microsoft's $69bn acquisition of Activision Blizzard in 2023 was partly about the same strategy: own the games, lock in the platform.
Applications
How Firms Use YED & XED
Recession-proof portfolios (YED): Firms selling high-YED luxury goods hedge by also owning low-YED necessity brands. LVMH, Unilever, and P&G all do this.
Pricing strategy (XED): If your good has close substitutes (high positive XED), a price rise will rapidly lose customers. Keep prices competitive.
Complementary pricing (XED): Sell the razor cheap, profit from blades. Sell the printer cheap, profit from cartridges. Negative XED makes the complement a profit engine.
Market entry strategy: A new entrant with a lower price (substituting for an existing firm) will gain demand proportional to the XED between their product and the incumbent's.
Government policy: YED helps predict tax revenue cyclicality — luxury good taxes collapse in recessions. Necessity taxes are more stable revenue streams.
Evaluation
Evaluating YED & XED
Strengths
YED helps firms plan production across the economic cycle
XED enables precise pricing strategy relative to competitors
Useful for governments forecasting tax revenues in different economic conditions
Explains observed market behaviour (luxury collapse in recessions)
Limitations
Income is hard to measure precisely — which income measure? Real or nominal?
YED and XED change over time as tastes and substitutes evolve
Assumes ceteris paribus — in reality many variables shift simultaneously
Classifying goods as inferior/normal may vary by income group or region
Essay Tip: When applying YED/XED to a business context, always consider which direction the economy is moving — the same firm can face very different demand conditions in boom vs recession. A strong evaluative point is that elasticity values are estimates that vary by time period, region, and consumer segment.
Glossary
Key Terms
YED
Income elasticity of demand. Measures responsiveness of Qd to a change in consumer income.
XED
Cross elasticity of demand. Measures responsiveness of Qd of Good A to a price change of Good B.
Normal Good
YED > 0. Demand rises as income rises. Necessities (0–1) and luxuries (>1).
Inferior Good
YED < 0. Demand falls as income rises — consumers switch to preferred alternatives.
Substitute
XED > 0. Goods that can replace each other. Price of one rises → demand for other rises.
Complement
XED < 0. Goods used together. Price of one rises → demand for other falls.
Summary · Topic 1.1
What You've Covered
📈 YED
›Formula: % ΔQd ÷ % ΔIncome
›Positive = normal good; Negative = inferior good
›YED > 1 = luxury; 0 < YED < 1 = necessity
›Rolls-Royce (luxury) vs Aldi (inferior substitute)
🔗 XED
›Formula: % ΔQd(A) ÷ % ΔP(B)
›Positive = substitutes; Negative = complements
›Zero = unrelated goods
›Sony PS5: consoles vs games (complement lock-in)
Question 1 of 8 · Income & Cross Elasticity
YED is positive and greater than 1. How is this good best classified?
A
Inferior good
B
Normal necessity
C
Luxury good
D
Giffen good
Answer · Question 1
YED is positive and greater than 1. How is this good best classified?
A
Inferior good
B
Normal necessity
C
Luxury good
D
Giffen good
Correct: C. YED > 1 means demand rises more than proportionately as income rises — the definition of a luxury good. YED between 0 and 1 = normal necessity. YED < 0 = inferior good. A Giffen good is a theoretical extreme where demand rises as price rises (unrelated to income elasticity).
Question 2 of 8 · Income & Cross Elasticity
During the 2008-09 recession, which business most likely saw demand rise as incomes fell?
A
Ferrari
B
Aldi
C
Louis Vuitton
D
Rolls-Royce
Answer · Question 2
During the 2008-09 recession, which business most likely saw demand rise as incomes fell?
A
Ferrari
B
Aldi
C
Louis Vuitton
D
Rolls-Royce
Correct: B. Aldi sells budget groceries — an inferior good relative to premium supermarkets. As incomes fell, consumers switched down to cheaper alternatives, boosting Aldi's market share from ~4% to over 10%. Ferrari, Louis Vuitton, and Rolls-Royce all have high positive YED — their sales collapsed in 2009.
Question 3 of 8 · Income & Cross Elasticity
The XED between two goods is −0.8. What does this tell us about the relationship between the goods?
A
They are substitutes
B
They are unrelated goods
C
They are complements
D
Good A is an inferior good
Answer · Question 3
The XED between two goods is −0.8. What does this tell us about the relationship between the goods?
A
They are substitutes
B
They are unrelated goods
C
They are complements
D
Good A is an inferior good
Correct: C. A negative XED indicates complements — goods used together. If the price of Good B rises, demand for Good A falls. The magnitude (0.8) tells us how strong the relationship is — a relatively strong complementary link.
Question 4 of 8 · Income & Cross Elasticity
Microsoft raises the price of Xbox Game Pass. What is the most likely effect on PlayStation 5 sales?
A
PS5 sales fall — they are complements
B
PS5 sales rise — they are substitutes
C
PS5 sales are unaffected
D
PS5 sales fall — XED is negative
Answer · Question 4
Microsoft raises the price of Xbox Game Pass. What is the most likely effect on PlayStation 5 sales?
A
PS5 sales fall — they are complements
B
PS5 sales rise — they are substitutes
C
PS5 sales are unaffected
D
PS5 sales fall — XED is negative
Correct: B. PlayStation and Xbox are substitutes — positive XED. When the price of one rises, demand for the other rises as consumers switch platforms. This is exactly why Sony monitors Microsoft's pricing decisions closely.
Question 5 of 8 · Income & Cross Elasticity
A good has YED = 0.3. Which statement best describes this good?
A
Inferior good — demand falls as income rises
B
Luxury good — demand rises more than proportionately
C
Normal necessity — demand rises, but less than proportionately
D
Income inelastic — demand is completely unaffected by income
Answer · Question 5
A good has YED = 0.3. Which statement best describes this good?
A
Inferior good — demand falls as income rises
B
Luxury good — demand rises more than proportionately
C
Normal necessity — demand rises, but less than proportionately
D
Income inelastic — demand is completely unaffected by income
Correct: C. YED = 0.3 is positive (normal good) but less than 1 (less than proportionate rise) — a normal necessity. Examples: food, electricity, basic clothing. YED = 0 would be perfectly income inelastic; YED > 1 would be luxury.
Question 6 of 8 · Income & Cross Elasticity
Sony prices its PlayStation 5 console near cost price. Which economic concept best explains this strategy?
A
Positive YED — console demand rises with income
B
Negative XED — consoles and games are complements; low console price drives high game revenue
C
Positive XED — consoles are substitutes for games
D
Inelastic demand — console buyers are insensitive to price
Answer · Question 6
Sony prices its PlayStation 5 console near cost price. Which economic concept best explains this strategy?
A
Positive YED — console demand rises with income
B
Negative XED — consoles and games are complements; low console price drives high game revenue
C
Positive XED — consoles are substitutes for games
D
Inelastic demand — console buyers are insensitive to price
Correct: B. Consoles and games are strong complements (XED < 0). By pricing consoles low, Sony maximises the number of consoles sold, which drives game, subscription (PS Plus), and DLC purchases — where the real profit margin lies. This is the "razor and blades" pricing model.
Question 7 of 8 · Income & Cross Elasticity
Petrol prices rise sharply. What is the most likely effect on demand for large SUVs, according to XED theory?
A
Demand for SUVs rises — they are substitutes for petrol
B
Demand for SUVs is unchanged — they are unrelated goods
C
Demand for SUVs falls — petrol and cars are complements
D
Demand for SUVs rises — higher petrol costs increase car demand
Answer · Question 7
Petrol prices rise sharply. What is the most likely effect on demand for large SUVs, according to XED theory?
A
Demand for SUVs rises — they are substitutes for petrol
B
Demand for SUVs is unchanged — they are unrelated goods
C
Demand for SUVs falls — petrol and cars are complements
D
Demand for SUVs rises — higher petrol costs increase car demand
Correct: C. Petrol and cars (especially fuel-heavy SUVs) are complements — XED is negative. A large rise in petrol prices makes running an SUV more expensive overall, reducing demand for them. This is why the 2022 energy crisis accelerated EV adoption as consumers switched to a different complement (electricity and EVs).
Question 8 of 8 · Income & Cross Elasticity
A government wants to raise tax revenue in a recession when incomes are falling. Which type of good should it tax to maximise revenue stability?
A
Luxury goods with high positive YED
B
Inferior goods with negative YED
C
Normal necessities with low positive YED
D
Goods with high positive XED
Answer · Question 8
A government wants to raise tax revenue in a recession when incomes are falling. Which type of good should it tax to maximise revenue stability?
A
Luxury goods with high positive YED
B
Inferior goods with negative YED
C
Normal necessities with low positive YED
D
Goods with high positive XED
Correct: C. Normal necessities (YED between 0 and 1) are relatively insensitive to income changes — demand holds up even in a recession. Taxing luxury goods (high YED) is risky because their demand collapses in downturns, reducing tax revenue precisely when the government needs it most. This is why VAT on food (a necessity) is zero-rated but alcohol duty (more discretionary) fluctuates with the economic cycle.