What you'll learn
This guide covers everything you need to know about demand for the Pearson Edexcel International IGCSE Economics examination. You'll master how consumer behaviour creates market demand, why demand curves slope downwards, and how various factors shift demand. Understanding demand is essential for analysing market behaviour and forms the foundation for studying price determination and market equilibrium.
Key terms and definitions
Demand — the quantity of a good or service consumers are willing and able to purchase at a given price over a specific time period
Effective demand — desire for a product backed by the ability to pay for it
Law of demand — as price falls, quantity demanded rises (and vice versa), assuming ceteris paribus
Demand curve — a graphical representation showing the relationship between price and quantity demanded
Individual demand — the demand of a single consumer for a good or service
Market demand — the total demand for a good or service from all consumers in a market
Movement along the demand curve — a change in quantity demanded caused solely by a price change
Shift of the demand curve — a change in demand at every price level caused by non-price factors
Core concepts
Understanding demand and the law of demand
Demand represents more than wanting something. A student might want a new iPhone, but unless they have £800 and are willing to spend it, this want does not constitute effective demand. Only when desire is backed by purchasing power does it become economically relevant.
The law of demand states an inverse relationship exists between price and quantity demanded. When Tesco reduces the price of bread from £1.20 to £0.90, consumers typically buy more loaves. This occurs for three reasons:
The income effect: When prices fall, consumers' real income increases. They can afford to buy more with the same nominal income. If petrol prices drop from £1.60 to £1.40 per litre, drivers have extra money to purchase additional litres or other goods.
The substitution effect: Lower prices make goods more attractive relative to alternatives. When chicken prices fall but beef prices remain constant, consumers substitute chicken for beef in their shopping baskets.
Diminishing marginal utility: Each additional unit consumed provides less satisfaction than the previous one. Consumers will only purchase additional units if prices decrease to reflect this lower utility. Your first bottle of water on a hot day provides significant satisfaction, but the fifth bottle offers minimal additional benefit.
The demand curve and market demand
The demand curve slopes downward from left to right, illustrating the inverse price-quantity relationship. Price appears on the vertical (y) axis, while quantity demanded appears on the horizontal (x) axis.
Constructing a demand curve requires a demand schedule:
| Price per kg (£) | Quantity demanded (kg per week) |
|---|---|
| 5.00 | 100 |
| 4.00 | 200 |
| 3.00 | 350 |
| 2.00 | 550 |
| 1.00 | 800 |
Individual demand curves represent single consumers' purchasing behaviour. Market demand aggregates all individual demands. If Manchester has 50,000 households each demanding one loaf weekly at £1.00, and 30,000 households each demanding one loaf at £1.20, market demand differs at these price points.
Market demand curves are typically smoother than individual curves because they aggregate numerous consumers with varied preferences and income levels.
Movements along versus shifts of the demand curve
This distinction is critical for examination success.
Movements along the demand curve occur exclusively when the product's own price changes, with all other factors constant (ceteris paribus).
- A price rise from £5 to £7 causes a contraction in demand (movement up and left along the curve)
- A price fall from £5 to £3 causes an extension in demand (movement down and right along the curve)
The curve itself doesn't move. Quantity demanded changes, but demand conditions remain constant.
Shifts of the demand curve occur when non-price factors change demand at every price level.
A rightward shift (increase in demand) means consumers demand more at every price point. The entire curve moves right, parallel to the original.
A leftward shift (decrease in demand) means consumers demand less at every price point. The entire curve moves left, parallel to the original.
Non-price determinants of demand (conditions of demand)
Six main factors shift demand curves:
1. Consumer income
For normal goods, rising income increases demand. As Caribbean economies grow and household incomes rise, demand for smartphones, restaurant meals, and international travel increases. The demand curve shifts right.
For inferior goods, rising income decreases demand. When families earn more, they might replace basic own-brand products with premium alternatives, reducing demand for inferior goods. The demand curve shifts left.
2. Population size and structure
Population growth increases market demand. The UK's population increased from 59 million (2001) to 67 million (2021), raising demand for housing, food, and healthcare.
Population structure matters equally. An ageing population increases demand for healthcare services, walking aids, and cruise holidays while reducing demand for children's toys and school uniforms.
3. Tastes and preferences
Fashion, trends, and cultural shifts significantly impact demand. Celebrity endorsements can boost demand for particular trainers or clothing brands. Health awareness campaigns have increased demand for organic vegetables and decreased demand for sugary drinks in many developed nations.
Advertising aims explicitly to shift demand curves rightward by influencing preferences.
4. Prices of related goods
Substitute goods satisfy similar needs. Examples include Coca-Cola and Pepsi, butter and margarine, or bus and train travel. When substitute prices rise, demand for the alternative increases. If Netflix raises subscription prices, demand for Disney+ might increase as consumers switch providers.
Complementary goods are consumed together. Examples include cars and petrol, printers and ink cartridges, or smartphones and data plans. When complementary goods' prices fall, demand for the related product increases. Cheaper flights to Spain boost demand for Spanish hotel rooms.
5. Interest rates
Higher interest rates increase borrowing costs, reducing demand for goods purchased on credit—particularly cars, furniture, and houses. They also make saving more attractive than spending, decreasing current consumption.
Lower interest rates have the opposite effect, stimulating demand for credit-financed purchases.
6. Consumer confidence and expectations
When consumers expect future economic growth, rising incomes, or job security, they increase current spending. Demand curves shift right.
During recessions or uncertainty (such as during the COVID-19 pandemic), consumers reduce spending and increase precautionary saving. Demand curves shift left, particularly for non-essential goods.
Exceptions to the law of demand
While rare, some goods don't follow standard demand patterns:
Giffen goods are inferior goods forming a large proportion of poor consumers' budgets. If staple food prices rise significantly, consumers become so much poorer they cannot afford variety. They buy even more of the staple food, reducing purchases of everything else. This theoretical concept has limited real-world evidence.
Veblen goods are luxury items where higher prices increase desirability because they signal status and exclusivity. Designer handbags, luxury cars, and prestigious watches might experience increased demand when prices rise, as higher prices enhance their appeal to status-conscious buyers.
Speculative demand occurs when consumers expect future price rises. During housing booms, rising house prices might increase demand as buyers rush to purchase before further increases. This creates asset bubbles.
Worked examples
Example 1: Interpreting demand curve movements (4 marks)
Question: The price of cinema tickets in London falls from £12 to £9. Using a diagram, explain the likely effect on the quantity demanded of cinema tickets.
Answer:
[Draw a standard downward-sloping demand curve, labelled D, with price on the y-axis and quantity on the x-axis. Mark point A at £12 and point B at £9 on the same curve, with B to the right of A]
The fall in price from £12 to £9 causes a movement along the demand curve from point A to point B (1 mark). This represents an extension in demand (1 mark). Quantity demanded increases because cinema tickets become more affordable relative to consumer incomes and substitute entertainment options (1 mark). More consumers find the lower price acceptable given the satisfaction they expect to receive from watching films (1 mark).
Example 2: Explaining demand shifts (6 marks)
Question: Explain two factors that might cause an increase in demand for electric vehicles in the UK.
Answer:
Government subsidies and grants reduce the effective price consumers pay, making electric vehicles more affordable compared to petrol cars (1 mark). This increases consumers' willingness and ability to purchase electric vehicles at all price points, shifting the demand curve to the right (1 mark).
Rising environmental awareness has changed consumer preferences (1 mark). As more people prioritize reducing carbon emissions and air pollution, tastes shift in favour of electric vehicles (1 mark). Media coverage of climate change and social pressure to adopt sustainable transportation increase the desirability of electric vehicles (1 mark), causing demand to increase at every price level (1 mark).
Example 3: Analysing related goods (4 marks)
Question: Coffee and tea are substitute goods. Explain the effect on demand for tea if coffee prices increase significantly.
Answer:
Coffee and tea are substitutes because they satisfy similar consumer needs for hot caffeinated beverages (1 mark). When coffee prices rise, consumers seeking to maintain their beverage consumption at lower cost will switch to the relatively cheaper alternative (1 mark). This increases demand for tea at all price levels, shifting the tea demand curve to the right (1 mark). More consumers will purchase tea at each price point because it now represents better value for money compared to the more expensive coffee (1 mark).
Common mistakes and how to avoid them
Confusing "demand" with "quantity demanded": Demand refers to the entire relationship between price and quantity (the whole curve). Quantity demanded refers to a specific amount at a particular price (one point on the curve). Always use precise terminology.
Shifting curves when you should show movements: Price changes of the good itself cause movements along the curve, not shifts. Only non-price factors shift curves. Draw your diagrams carefully and explain whether you're showing a movement or a shift.
Forgetting ceteris paribus: The law of demand only holds when other factors remain constant. Always acknowledge this assumption when explaining demand relationships.
Misidentifying normal and inferior goods: Normal goods see demand increase with income; inferior goods see demand decrease with income. Examples matter—instant noodles are typically inferior, while restaurant meals are normal goods.
Weak explanations of why demand curves slope downward: Don't simply state "price falls, demand rises." Explain the income effect, substitution effect, or diminishing marginal utility to demonstrate understanding.
Confusing complements and substitutes: Substitutes replace each other (when one's price rises, demand for the other increases). Complements are used together (when one's price rises, demand for the other decreases). Learn clear examples of each.
Exam technique for "The Market System: Demand"
Command word precision: "State" requires brief factual points (1 mark each). "Explain" requires causes or reasons with development (2-3 marks). "Analyse" requires breaking down relationships with logical chains (4-6 marks). "Evaluate" requires weighing significance and making judgments (8+ marks).
Always use diagrams when relevant: For questions about price changes, demand shifts, or market analysis, a correctly labelled diagram often earns marks independently of your written explanation. Label axes (Price, Quantity), curves (D, D1), and relevant points (A, B).
Link to real-world contexts: Questions often specify contexts (e.g., "in developing countries" or "for luxury goods"). Tailor your examples accordingly. Generic answers earn fewer marks than context-specific responses.
Develop your explanations: Single-sentence points rarely earn full marks. Use logical connectives: "This is because...", "As a result...", "This leads to...". Chain your reasoning to show economic understanding rather than simple recall.
Quick revision summary
Demand represents consumers' willingness and ability to purchase goods at various prices. The law of demand states that price and quantity demanded are inversely related due to income effects, substitution effects, and diminishing marginal utility. Price changes cause movements along demand curves (extensions or contractions), while non-price factors—income, population, tastes, related goods' prices, interest rates, and consumer confidence—shift entire demand curves. Market demand aggregates all individual demands. Master the distinction between movements and shifts, understand how related goods interact, and always support explanations with clear, labelled diagrams for examination success.