What you’ll learn8 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 objective2.5.4(HL)—PED along a straight-line demand curve• PED changes along a straight-line downward-sloping demand curve• Diagram [HL]: PED along a straight-line demand curveSyllabus 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 objective2.5.6(HL)—PED for primary commodities• Primary commodities generally have lower PED than manufactured products• Lower substitutability and necessity can reduce responsivenessSyllabus 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 objective2.5.8(HL)—Importance of YED• YED helps firms predict demand changes after income changes• YED helps explain changes in the sectoral structure of an economySyllabus objective