Pearson Edexcel · A-Level · Economics B
Course version: 9EB0 · Version from Sept 2015
C) Interpretation of numerical values of income elasticity of demand
Full specification wording
Income elasticity of demand (YED): c) Interpretation of numerical values of income elasticity of demand
Income elasticity of demand (YED) measures the responsiveness of quantity demanded to a change in real income.
Checked against the Pearson Edexcel 9EB0 specification (opens in a new tab) on .
- Point 3 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Income elasticity of demand (YED) measures the responsiveness of quantity demanded to a change in real income. Interpreting its numerical value requires analysing both the sign and the magnitude. A positive YED indicates a normal good, where demand rises as income increases. Within normal goods, a value between 0 and 1 signifies a necessity (income inelastic), meaning demand grows proportionately less than income. A value greater than 1 denotes a luxury good (income elastic), where demand grows proportionately more than income. Conversely, a negative YED indicates an inferior good; as income rises, consumers switch to higher-quality alternatives, causing demand for the inferior good to fall.
For example: If a 10% increase in income leads to a 15% increase in demand for restaurant meals, the YED is +1.5, confirming it is a luxury good.
What earns the marks
- Identifies a YED greater than 0 as a normal good.
- Identifies a YED less than 0 as an inferior good.
- Distinguishes between necessities (YED between 0 and 1) and luxuries (YED greater than 1).
- Interprets a specific numerical value in context, such as stating that a YED of +2.5 means a 1% rise in income causes a 2.5% rise in quantity demanded.
Common mistakes and how to put them right
Confusing the sign of YED with PED.
Put it right: YED can be positive or negative, and the sign is crucial for identifying normal versus inferior goods, whereas PED is typically negative.
Assuming a YED of 0.5 means it is an inferior good.
Put it right: 0.5 is positive, so it is a normal good (specifically a necessity), not an inferior good.
Misinterpreting the magnitude of a negative YED.
Put it right: A YED of -2 is income elastic (magnitude greater than 1) but for an inferior good, meaning demand falls significantly when income rises.
Exam tips
- Always state the sign when calculating or interpreting YED to clearly identify the type of good.
- Use the terms 'income elastic' and 'income inelastic' alongside 'luxury' and 'necessity' to demonstrate precise economic vocabulary.
- When given a YED value in a multiple-choice question, first check the sign to eliminate incorrect options regarding normal or inferior goods.
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The start of the Income elasticity of demand (YED): c) Interpretation of numerical values of income elasticity of demand lesson, made from checked teaching notes for this specification point.
Have a go first
A product has an estimated income elasticity of demand of -0.4. How should this product be classified based on this numerical value?
Listen
Income elasticity of demand (YED) measures the responsiveness of quantity demanded to a change in real income. Interpreting its numerical value requires analysing both the sign and the magnitude. A positive YED indicates a normal good, where demand rises as income increases. Within normal goods, a value between 0 and 1 signifies a necessity (income inelastic), meaning demand grows proportionately less than income. A value greater than 1 denotes a luxury good (income elastic), where demand grows proportionately more than income. Conversely, a negative YED indicates an inferior good; as income rises, consumers switch to higher-quality alternatives, causing demand for the inferior good to fall. For example, if a 10% increase in income leads to a 15% increase in demand for restaurant meals, the YED is +1.5, confirming it is a luxury good. A strong answer earns marks for these points. Identifies a YED greater than 0 as a normal good. Identifies a YED less than 0 as an inferior good. Distinguishes between necessities (YED between 0 and 1) and luxuries (YED greater than 1). Interprets a specific numerical value in context, such as stating that a YED of +2.5 means a 1% rise in income causes a 2.5% rise in quantity demanded. A common slip: Confusing the sign of YED with PED. Instead, YED can be positive or negative, and the sign is crucial for identifying normal versus inferior goods, whereas PED is typically negative. Exam tip: Always state the sign when calculating or interpreting YED to clearly identify the type of good.
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Key words
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Income elasticity of demand (YED)
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Normal good
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Inferior good
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Luxury good
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See every definition
- Income elasticity of demand (YED)
- Measures the responsiveness of quantity demanded to a change in real income.
- Normal good
- A good with a positive YED, where demand rises as income increases.
- Inferior good
- A good with a negative YED, where demand falls as income rises because consumers switch to higher-quality alternatives.
- Luxury good
- A normal good with a YED greater than 1, where demand grows proportionately more than income.
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