A-Level Economics May/June 2024 Q3(a): With the help of a formula, explain what is meant by the income elasticity of demand fo…

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  Income elasticity of demand (YED) measures the responsiveness of the quantity demanded for a product following a change in the real income of consumers. It is a numerical measure that indicates both the direction and the magnitude of the change in demand.

  The formula for calculating YED is:

  $YED = \frac{\% \text{ change in quantity demanded}}{\% \text{ change in income}}$

  (AO1_1, AO1_2)

  The value of the YED coefficient determines the nature of the good. For a normal good, YED is positive (YED > 0), meaning that as income rises, demand for the product also rises. Normal goods can be further categorised. If demand is income elastic (YED > 1), the percentage rise in demand is greater than the percentage rise in income; these are often luxury goods. If demand is income inelastic (0 < YED < 1), the percentage rise in demand is less than the percentage rise in income; these are often necessities. (AO1_3)

  The extent to which demand for a product will rise at the same rate as consumer income depends entirely on the YED coefficient for that specific product. The statement that demand will always rise at the same rate as income is only true in the very specific case where a product has a YED of exactly +1 (unitary income elasticity). (AO2_1)

  For most normal goods, this is not the case. For a luxury good like a sports car (e.g., YED = +2.5), a 10% rise in income would lead to a 25% rise in demand, a much faster rate. For a necessity like milk (e.g., YED = +0.4), a 10% rise in income would lead to only a 4% rise in demand, a much slower rate. Therefore, for the vast majority of normal goods, demand does not rise at the same rate as income. (AO2_2)

  Furthermore, the statement completely ignores the existence of inferior goods. These products have a negative YED (YED < 0). For an inferior good, such as own-brand budget pasta, an increase in consumer income leads to a decrease in the quantity demanded, as consumers switch to higher-quality alternatives. For example, if YED = -0.5, a 10% rise in income would cause a 5% fall in demand. In this case, demand does not rise at all; it falls. (AO2_3)

  In evaluation, the proposition that demand for a product will always rise at the same rate as income is fundamentally incorrect. It only describes one very specific theoretical possibility (YED = 1) and fails to account for the far more common scenarios of income elastic necessities, income elastic luxuries, and income-related decreases in demand for inferior goods. The relationship is highly variable and product-dependent. (AO3_1)

  In conclusion, the extent to which demand changes with income is rarely, if ever, at the same rate. The YED coefficient reveals a wide spectrum of possible outcomes, from demand rising faster than income (luxuries), to rising slower than income (necessities), to falling as income rises (inferior goods). Therefore, the initial statement is not a valid generalisation. (AO3_2)

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  How the marks are awarded

  • AO1_1 — The formula for YED is stated accurately as the percentage change in quantity demanded divided by the percentage change in income.
  • AO1_2 — The first paragraph provides a clear and accurate definition of YED as a measure of the responsiveness of quantity demanded to a change in consumer income.
  • AO1_3 — The second paragraph explains the distinction between income elastic (YED > 1) and income inelastic (0 < YED < 1) demand for normal goods.
  • AO2_1 — The third paragraph begins the analysis by explaining that the rate of change in demand is determined by the specific coefficient value of YED.
  • AO2_2 — The analysis of normal goods is developed by explaining the different outcomes for luxuries (demand rises faster than income) and necessities (demand rises slower than income).
  • AO2_3 — The analysis is broadened to include inferior goods, explaining that demand falls as income rises (YED < 0), which directly contradicts the premise of the question.
  • AO3_1 — A considered evaluation is made by weighing the different outcomes and explicitly stating that the claim is only true in the specific and rare case of YED = 1.
  • AO3_2 — A valid conclusion is reached, summarising that the relationship is variable and dependent on the YED coefficient, meaning demand will not 'always' rise at the same rate as income.

  Common mistakes

  • Confusing YED with Price Elasticity of Demand (PED) and discussing price changes instead of income changes.
  • Defining YED correctly but failing to analyse the 'extent' part of the question, i.e., not explaining what coefficients greater than, less than, or equal to 1 mean for the rate of change.
  • Only discussing normal goods and completely omitting inferior goods, which is a crucial part of the analysis required to challenge the word 'always'.
  • Misinterpreting the formula, for example by inverting it (change in income / change in demand).

  Examiner tip: Always break down absolute statements in a question, such as 'always' or 'never', by using the full range of theoretical possibilities to analyse and evaluate the claim.

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