What does a positive cross elasticity of demand value tell you

• →Cross elasticity of demand measures the responsiveness of the quantity demanded of one good to a change in the price of another good, calculated as the percentage change in quantity demanded of good A divided by the percentage change in the price of good B.
• →A positive XED value indicates that the two goods in question are substitutes which means that they compete to satisfy the same consumer want. When the price of good B rises, consumers switch away from it towards good A, causing demand for good A to increase.
• →As a result, the quantity demanded of the two goods moves in the same direction relative to the price change, which is what produces the positive sign. For example, if the price of Pepsi rises, the demand for Coca-Cola is likely to increase, yielding a positive XED between them.
• →The larger the positive value, the closer the substitutes are considered to be, since a small price change in one good triggers a proportionally larger shift in demand for the other. Firms operating in markets with high positive XED values face intense competitive pressure, as consumers switch easily between their products and rivals' products.

• →The sign of XED is decisive: a positive value always indicates substitute goods; a negative value indicates complementary goods; a value of zero suggests the goods are unrelated. Confusing the sign is a common source of lost marks.
• →The magnitude matters as well as the sign: a XED of +0.1 suggests weak substitutability, while a XED of +3.0 suggests the goods are very close substitutes and that demand is highly sensitive to a competitor's price change.
• →Substitutes compete on the same want: goods do not have to be identical to be substitutes — they simply need to satisfy the same consumer need, such as bus travel and train travel, or butter and margarine.
• →Relevance to firms' pricing decisions: a business aware that its product has a high positive XED with a rival's product knows that any price cut by that rival will draw significant demand away from it; this shapes decisions on pricing, branding, and product differentiation.
• →Direction of causation in the calculation: XED examines the effect of a price change in another good on the quantity demanded of this good — students must be careful not to reverse the relationship when interpreting or calculating the coefficient.

This question tests understanding of cross elasticity of demand as a measure of the relationship between goods in a market, specifically the interpretation of a positive coefficient as evidence of substitutability. It is assessed under Edexcel spec point 1.2.3.c — which covers the concept of cross elasticity of demand, including how to calculate it, interpret its sign and magnitude, and explain what those values mean for the relationship between goods. Examiners are looking for precision in distinguishing between the sign and size of XED, and for the ability to apply the concept to real-world market contexts rather than simply stating a definition.

Examined 3 times across Edexcel since 2018.

The tariff has ranged from 1 mark to 8 marks, indicating that this concept has been tested at both the recall and extended reasoning levels on the same paper.

• →How Markets Work — understanding how the price mechanism operates provides the foundation for grasping why a price change in one market affects demand in another, which underpins the interpretation of any XED value.