EC10: Intermarket Relationships
How changes in one market affect others: complementary goods, substitute goods, derived demand, and cross-price elasticity of demand.
Intermarket Relationships
How changes in one market affect others: complementary goods, substitute goods, derived demand, and cross-price elasticity of demand.
Key Fact: Complementary goods are used together (cars and petrol). A price rise for one reduces demand for the complement.
Key Fact: Substitute goods are alternatives (Coke and Pepsi). A price rise for one increases demand for the substitute.
Key Fact: Cross-price elasticity (XED) = %ΔQd of A / %ΔP of B. Positive XED = substitutes; negative XED = complements.
Key Fact: Derived demand: demand for one good comes from demand for another. Demand for labour is derived from demand for the product workers make.
Key Fact: Changes ripple through the economy: a rise in oil prices affects transport, manufacturing, food prices, and household budgets.
📋 Key Vocabulary and Concepts
For Intermarket Relationships, you must know:
- Complementary goods
- Substitute goods
- Cross-price elasticity
- XED
- Derived demand
- Joint supply
- Intermarket relationship
❓ Practice Questions
Q1: Explain the difference between complementary and substitute goods, giving two examples of each.
Q2: Describe what is meant by derived demand and explain how it links product and factor markets.
Q3: Analyse how a significant rise in oil prices might affect other UK markets.
✅ Answers
- Complements: used together, price rise for one reduces demand for other (cars + petrol, smartphones + cases). Substitutes: alternatives, price rise for one increases demand for other (butter + margarine, train + bus).
- Derived demand means demand for a factor comes from demand for the product. E.g. demand for software developers comes from demand for apps. If housing demand falls, demand for construction workers falls. This links product markets to factor markets.
- Oil is an input for many industries: transport costs rise, manufacturing costs increase, consumers spend more on petrol (reducing disposable income for other goods), demand for electric vehicles rises. A single market change propagates through interconnected markets.
🎯 Exam Tips
- Always specify whether goods are complements or substitutes before predicting effects.
- XED sign: positive = substitutes, negative = complements.
- Use derived demand to explain employment changes: fewer houses → fewer bricklayers.
📝 Exam Technique
Economics Exam Tips:
When analysing intermarket relationships, use the CSR framework: Complements or Substitutes? Sign of XED? Ripple effects? No market operates in isolation.
When analysing intermarket relationships, use the CSR framework: Complements or Substitutes? Sign of XED? Ripple effects? No market operates in isolation.
⚠️ Common Errors
Watch Out!
Students often make mistakes here. Wrong: When the price of a good rises, demand for its substitute always increases by the same proportion. Correct: The extent of substitution depends on: how close the substitutes are, the time period (adjustment takes time), and consumer preferences (habit and brand loyalty reduce substitution). XED measures responsiveness but it varies — no automatic proportional relationship.
✍️ Model Answer
Full-Mark Response
Evaluate how the rise of streaming services has affected demand for cinema tickets and physical media.
A grade 9 response will: streaming is a close substitute for physical media (DVD/CD demand collapsed) but weaker substitute for cinema (different experience); cinema demand fell moderately (cinemas responded with premium experiences); conclude: close substitutes cause dramatic shifts, less similar substitutes cause more moderate shifts.
📊 AO Deep Dive
Assessment Objective Focus: Intermarket Relationships
AO1 — Knowledge: Demonstrate knowledge of Intermarket Relationships with precise business/economic terminology. Define key terms and state accurate factual information.
AO2 — Application: Apply knowledge of Intermarket Relationships to business scenarios and case studies. Use quantitative data where relevant to support your points.
AO3 — Analysis & Evaluation: Analyse and evaluate Intermarket Relationships by considering trade-offs, weighing costs against benefits, and reaching a reasoned judgement. Use connectives to show chains of reasoning.
Detailed Notes: Intermarket Relationships
Substitute and Complementary Goods
Markets are interconnected through substitute and complementary goods. Substitutes are goods that can replace each other in consumption — if the price of one rises, demand for the other increases. Cross elasticity of demand (XED) for substitutes is positive. UK examples include butter and margarine, bus travel and train travel, or Netflix and cinema tickets. Complements are goods consumed together — if the price of one rises, demand for the other falls. XED for complements is negative. Examples include printers and ink cartridges, fish and chips, or smartphones and phone cases.
Understanding these relationships is essential for predicting how a change in one market affects another. When the UK government increased the minimum price of alcohol in Scotland (2018), demand for soft drinks and mixer beverages in Scottish pubs increased as some consumers switched from spirits. When the price of petrol rises, demand for large, fuel-inefficient cars falls (complement relationship) whilst demand for electric vehicles and public transport rises (substitute relationship). Firms must anticipate these intermarket effects when setting prices or planning products.
Real-World Example
When Ofgem raised the UK energy price cap in October 2022, average household energy bills rose by over 80%. This affected multiple markets: demand for home insulation services surged (complement — cheaper to run a well-insulated home), demand for energy-efficient appliances like heat pumps increased (substitute for gas heating), and demand for pub meals fell as households had less disposable income after paying energy bills (income effect across markets).
Derived Demand and Joint Supply
Derived demand occurs when the demand for one good or factor of production results from the demand for something else. For example, the demand for lorry drivers is derived from the demand for goods that need transporting. The demand for steel is derived from the demand for cars, construction and machinery. If car sales fall, demand for steel falls too. Understanding derived demand helps explain why whole supply chains are affected when end-user demand changes — the 2020 pandemic reduced demand for new cars, which in turn reduced demand for automotive steel, car carpeting, and components.
Joint supply occurs when the production of one good simultaneously produces another. For example, when sheep are raised for meat (lamb), wool is also produced as a by-product. If demand for lamb increases, the supply of wool also increases, potentially lowering wool prices even though wool demand has not changed. In the UK, the dairy industry produces both milk and cream as joint products; the oil industry produces both petrol and diesel from crude oil. These joint supply relationships mean that changes in demand for one product can have unexpected effects on the market for another.
Real-World Example
The decline of UK coal mining provides a stark example of derived demand in reverse. As UK power stations switched from coal to natural gas and renewables (changing the derived demand for coal), entire supply chains were affected — demand for mining equipment fell, railway coal freight services declined, and mining communities lost their economic base. The last deep coal mine in the UK, Kellingley Colliery in North Yorkshire, closed in 2015, ending an industry that once employed over a million workers.
How Changes in One Market Ripple Through the Economy
Changes in one market can have far-reaching effects throughout the economy due to intermarket relationships. A significant price change in a major market (such as energy or housing) affects household budgets, which in turn changes demand across many other markets. The concept of the multiplier effect captures this: an initial change in spending leads to further rounds of spending as income circulates through the economy. When a major employer closes a factory, not only do the workers lose income (reducing demand in local shops and services), but the shops and services then reduce their own spending, creating a cascade of falling demand.
The COVID-19 pandemic demonstrated intermarket relationships dramatically. The closure of hospitality (restaurants, pubs, hotels) not only affected those businesses directly but also their suppliers (food wholesalers, breweries, linen services) and their workers (who then spent less on housing, retail, and entertainment). The UK government's furlough scheme was designed precisely to break these negative ripple effects by maintaining workers' incomes and therefore their spending across multiple markets.
Real-World Example
When the UK introduced a 5p (now 10p) charge for single-use plastic bags in 2015, demand for plastic carrier bags fell by over 80% in major supermarkets. This affected not only plastic bag manufacturers (reduced demand) but also increased demand for reusable bags (substitute), changed shopping habits (some consumers bought less if they forgot bags), and even affected bin liner sales (many people reused carrier bags as bin liners, so demand for purpose-made bin liners increased). A single policy change rippled through multiple interconnected markets.
Comparison: Substitutes vs Complements
| Feature | Substitute Goods | Complementary Goods |
|---|---|---|
| Definition | Goods that can replace each other | Goods consumed together |
| XED sign | Positive | Negative |
| Price of A rises, demand for B | Increases | Decreases |
| UK example 1 | Butter and margarine | Printers and ink cartridges |
| UK example 2 | Train and bus travel | Smartphones and phone insurance |
| Business implication | Compete for same customers | Bundle or discount together |
Additional Practice Questions
Q1: Explain how a significant rise in the price of petrol in the UK would affect at least three other markets, distinguishing between substitute and complement relationships.
Q2: Evaluate the importance of understanding intermarket relationships for a UK business when making pricing decisions.
Additional Model Answers
- A rise in petrol prices would affect multiple markets: (1) Demand for public transport (buses and trains) would increase as they are substitutes for car travel — commuters switch from driving to taking the bus or train to save money. (2) Demand for large, fuel-inefficient cars (such as SUVs) would decrease as these are complements to petrol — the total running cost of the car includes fuel, making large cars less attractive. (3) Demand for electric vehicles would increase as they are substitutes for petrol cars — the lower running cost of EVs becomes more attractive when petrol is expensive. Additionally, demand for home delivery services might increase (substitute for driving to shops), and demand for bicycle sales might increase (another substitute). These intermarket relationships show how a single price change ripples through the economy.
- Understanding intermarket relationships is crucial for effective pricing decisions. A firm that ignores these relationships may make decisions with unintended consequences. For example, if a UK cinema raises ticket prices without considering that streaming services are a substitute, it may lose customers to Netflix. Conversely, a firm that understands complementarity can use it strategically — Gillette sells razors cheaply (sometimes at a loss) because it knows demand for razor blades (the complement) will generate profit over time; similarly, games console makers like Sony sell hardware at thin margins because game sales drive profit. For derived demand businesses, understanding the end market is essential — a UK steel producer must monitor car industry forecasts because a downturn in car sales will reduce demand for its products. However, intermarket relationships can be complex and unpredictable — the strength of substitute and complement relationships varies, and new products can disrupt existing patterns (e.g. streaming disrupted the DVD/cinema relationship). On balance, understanding these relationships gives businesses a significant competitive advantage, but they must also remain alert to changing market dynamics.
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🎬 Video Resources
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