What you’ll learn5 learning objectivesChoose one objective for a focused lesson, or study the complete topic.2.5.1Concept of elasticity• Elasticity measures responsiveness between economic variables• Diagram: relatively elastic and relatively inelastic demandSyllabus objective2.5.2Price elasticity of demand• PED equals percentage change in quantity demanded divided by percentage change in price• PED has a theoretical range of values and indicates responsiveness of demand to price• Calculation: PED, change in price, quantity demanded, or total revenue from dataSyllabus objective2.5.3PED diagrams and revenue• PED can be perfectly elastic, perfectly inelastic, unitary, elastic, or inelastic• PED affects total revenue when price changes• Diagram: constant PED cases and unitary PED along a demand curve• Diagram: revenue changes when demand is price elastic or price inelasticSyllabus objective2.5.5Determinants and importance of PED• PED depends on number and closeness of substitutes, necessity, income proportion, and time• PED matters for firm pricing and government decision-makingSyllabus objective2.5.7Income elasticity of demand• YED equals percentage change in quantity demanded divided by percentage change in income• Positive YED identifies normal goods; negative YED identifies inferior goods• YED below one is typical of necessities; YED above one is typical of services and luxury goods• Diagram: income elastic, income inelastic, and inferior goods on an Engel curve• Calculation: YED, change in income, or quantity demanded from dataSyllabus objective