Consumer Surplus • We have defined Consumer Surplus in terms of demand curves. • Can we provide a formal definition inP terms of utility functions? Consumer Surplus and Indifference Curves Managerial Economics-Charles W. Upton D Consumer Surplus and Indifference Curves A Formal Definition Q A Formal Definition X X Budget Xo Xo Widgets Widgets Consumer Surplus and Indifference Curves Consumer Surplus and Indifference Curves A Formal Definition A Formal Definition X X X1 Xo Xo Widgets Consumer Surplus and Indifference Curves Widgets Consumer Surplus and Indifference Curves 1 A Formal Definition The Equation X • A consumer has income of xo X1 Xo Consumer Surplus = X1 - Xo Widgets Consumer Surplus and Indifference Curves Consumer Surplus and Indifference Curves The Equation • A consumer has income of xo • He gets the chance to purchase at a price p o • He purchases q o The Equation • • • • • A consumer has income of xo He gets the chance to purchase at a price p o He purchases q o Let his utility function be U(X, q) ∆ defines consumer surplus U(xo -poqo , qo ) = U(xo +∆, 0) Consumer Surplus and Indifference Curves Consumer Surplus and Indifference Curves The Equation The Equation U(xo-poqo, qo) = U(xo +∆, 0) U(xo-poqo, qo) = U(xo +∆, 0) Units of good purchased Consumer Surplus and Indifference Curves Amount to Units of spend on good other purchased goods. Consumer Surplus and Indifference Curves 2 The Equation U(xo-poqo, qo) = U(xo +∆, 0) Amount to Units ofthat would Dollars spend on good an equal represent other purchased increase in utility. goods. Consumer Surplus and Indifference Curves One of a Kind • A consumer has income of xo • He gets the chance to buy a one of a kind item for p o • His Utility Function is U(x,N) X = Dollars spend on everything but the item Consumer Surplus and Indifference Curves An Application • A consumer has income of xo • He gets the chance to buy a one of a kind item • Let One of a Kind • A consumer has income of xo • He gets the chance to buy a one of a kind item for p o • His Utility Function is U(x,N) Consumer Surplus and Indifference Curves One of a Kind • A consumer has income of xo • He gets the chance to buy a one of a kind item for p o • His Utility Function is U(x,N) X = Dollars spend on everything but the item N= 0 (doesn’t buy) N=1 (buys) Consumer Surplus and Indifference Curves Willingness to Pay • A consumer has income of xo • He gets the chance to a buy a one of a kind item U(xo -po , 1) = U(xo +∆, 0) • ∆ defines consumer surplus Consumer Surplus and Indifference Curves Consumer Surplus and Indifference Curves 3 Willingness to Pay • A consumer has income of xo • He gets the chance to a buy a one of a kind item • Let U(xo - θ, 1) = U(xo , 0) A Comparison Consumer Surplus U(xo -po , 1) = U(xo +∆, 0) • θ defines the maximum amount he is willing to pay Consumer Surplus and Indifference Curves A Comparison Consumer Surplus U(xo -po , 1) = U(xo +∆, 0) Willingness to Pay U(xo - θ, 1) = U(xo , 0) Consumer Surplus and Indifference Curves A Comparison Consumer Surplus U(xo -po , 1) = U(xo +∆, 0) Willingness to Pay U(xo - θ, 1) = U(xo , 0) ∆ + po ≠ θ Consumer Surplus and Indifference Curves A Comparison Consumer Surplus U(xo -po , 1) = U(xo +∆, 0) Willingness to Pay U(xo - θ, 1) = U(xo , 0) ∆ + po ≅ θ Consumer Surplus and Indifference Curves Consumer Surplus and Indifference Curves A Comparison Consumer Surplus U(xo -po , 1) = Willingness to Pay U(xo - θ, 1) = U(x , 0) U(xo +∆, 0) Suppose I amo given a rare beautiful painting. Consumer Surplus and Indifference Curves 4 A Comparison Consumer Surplus U(xo -po , 1) = Willingness to Pay U(xo - θ, 1) = U(x , 0) U(xo +∆, 0) Significant o consumer surplus. Consumer Surplus and Indifference Curves A Comparison Consumer Surplus U(xo -po , 1) = Willingness to Pay U(xo - θ, 1) = But0)wouldU(x I be , 0) U(xo +∆, o willing to pay that much? Consumer Surplus and Indifference Curves End ©2003 Charles W. Upton Consumer Surplus and Indifference Curves 5