Elasticities of Demand and Supply
Calculating and interpreting price, income and cross elasticities of demand and price elasticity of supply, including determinants and decision relevance.
How to study A-level Economics
Define the issue and affected agents, choose an appropriate model, build the causal chain with data, then evaluate assumptions, trade-offs and alternatives before judging.
Core concepts
Concept 1
Elasticity measures responsiveness as a proportionate change, allowing comparison across different units and scales.
Exam cue: Use the correct percentage-change numerator and denominator, preserving the sign where relevant.
Concept 2
Price elasticity of demand affects the relationship between price changes and total revenue.
Exam cue: Interpret magnitude and economic meaning, not just elastic or inelastic.
Concept 3
Time, spare capacity, substitutability, necessity and adjustment possibilities influence elasticity.
Exam cue: Apply the result to a firm's, worker's or government's objective and constraint.
Risk pitfalls and guardrails
Treating the slope of a curve as identical to elasticity.
Guardrail: Do not substitute a memorised diagram or generic advantage until you have identified the determinant, mechanism, affected agents and time horizon.
Calling a negative income elasticity an error.
Guardrail: Do not substitute a memorised diagram or generic advantage until you have identified the determinant, mechanism, affected agents and time horizon.
Assuming elasticity stays constant along every demand curve.
Guardrail: Do not substitute a memorised diagram or generic advantage until you have identified the determinant, mechanism, affected agents and time horizon.
Memory anchors
Price Elasticity of Demand
PED measures the responsiveness of quantity demanded to a change in price.
Income Elasticity of Demand
YED measures the responsiveness of demand to a change in income.
Cross Elasticity of Demand
XED measures the responsiveness of demand for one good to the price of another.
Price Elasticity of Supply
PES measures the responsiveness of quantity supplied to a change in price.
Inelastic
An inelastic response has a proportional quantity change smaller than the causal proportional change.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
Price rises by 10% and quantity demanded falls by 20%. What is price elasticity of demand?
Quantity demanded falls by 4% after an 8% price rise. How is demand classified?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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