CHAPTER 3 Chapter 3

CHAPTER 3 RATIONAL CONSUMER CHOICE McGraw-Hill/IrwinCopyright © 2011 by The McGraw-Hill Companies, Inc. All rights reserved. Chapter 3

3-3 Chapter Outline The opportunity set or budget constraint Consumer preferences The best feasible bundle An application of the rational choice model

3-4 Budget Limitation A bundle: a particular combination of two or more goods. Budget constraint: the set of all bundles that exactly exhaust the consumer’s income at given prices. – Its slope is the negative of the price ratio of the two goods.

3-5 Figure 3.1: Two Bundles of Goods Food (kg/wk) Shelter (sq m/wk) 0

3-6 Figure 3.2: The Budget Line, or Budget Constraint Food (kg/wk) Shelter (sq m/wk)

3-7 Budget shifts due to price or income changes If the price of ONLY one good changes… – The slope of the budget constraint changes. If the price of both goods change by the same proportion… – The budget constraint shifts parallel to the original one. If income changes …. – The budget constraint shifts parallel to the original one.

3-8 Figure 3.3: The Effect of a Rise in the Price of Shelter Food (kg/wk) Shelter (sq m/wk)

3-9 Figure 3.4: The Effect of Cutting Income by Half Food (kg/wk) Shelter (sq m/wk)

3-10 Figure 3.5: The Budget Line with the Composite Good Y (units/wk) X (units/wk)

3-11 Figure 3.6: A Quantity Discount Gives Rise to a Nonlinear Budget Constraint Y (R/mo)

3-12 Figure 3.7: Budget Constraints Following Theft of Petrol, Loss of Cash Petrol (R/mo) Y (R/mo) M-550 M 10 M

3-13 Properties of Preference Orderings Completeness: the consumer is able to rank all possible combinations of goods and services. More-Is-Better: other things equal, more of a good is preferred to less. Transitivity: for any three bundles A, B, and C, if one prefers A to B and prefers B to C, then one always prefers A to C. Covexity: mixtures of goods are preferable to extremes.

3-14 Figure 3.8: Generating Equally Preferred Bundles Food (kg/wk) Shelter (sq m/wk)

3-15 Indifference Curves Indifference curve: a set of bundles among which the consumer is indifferent. Indifference map: a representative sample of the set of a consumer’s indifference curves, used as a graphical summary of her preference ordering.

3-16 Properties of Indifference Curves Indifference curves … 1.Are Ubiquitous. Any bundle has an indifference curve passing through it. 2.Are Downward-sloping. This comes from the “more-is-better” assumption. 3.Cannot cross. 4.Become less steep as we move downward and to the right along them. This property is implied by the convexity property of preferences.

3-17 Figure 3.9: An Indifference Curve Food (kg/wk) Shelter (sq m/wk) 0

3-18 Figure 3.10: Part of an Indifference Map Food (kg/wk) Shelter (sq m/wk) 0

3-19 Figure 3.11: A Three-Dimensional Utility Surface U1U1 U

3-20 Figure 3.12: Indifference Curves as Projections 0

3-21 Figure 3.13: Why Two Indifference Curves Do Not Cross Food (kg/wk) Shelter (sq m/wk) 0

3-22 Trade-offs Between Goods Marginal rate of substitution (MRS): the rate at which the consumer is willing to exchange the good measured along the vertical axis for the good measured along the horizontal axis. – Equal to the absolute value of the slope of the indifference curve.

3-23 Figure 3.14: The Marginal Rate of Substitution Food (kg/wk) Shelter (sq m/wk) 0

3-24 Figure 3.15: Diminishing Marginal Rate of Substitution Food (kg/wk) Shelter (sq m/wk)

3-25 Figure 3.16: People with Different Tastes Potatoes (kg/wk) Rice (kg/wk) Carlos’s 0 0

3-26 The Best Feasible Bundle Consumer’s Goal: to choose the best affordable bundle. – The same as reaching the highest indifference curve she can, given her budget constraint. – For convex indifference curves. the best bundle will always lie at the point of tangency between the budget line and the indifference curve.

3-27 Figure 3.17: The Best Affordable Bundle Food (kg/wk) Shelter (sq m/wk)

3-28 Figure 3.18: A Corner Solution Food (kg/wk) Shelter (sq m/wk) 0

3-29 Figure 3.19: Equilibrium with Perfect Substitutes Coke (litre/day) Pepsi (litre/day)

3-30 Cash or Food Stamps? Food Stamp Program – Objective - to alleviate hunger. – How does it work? People whose incomes fall below a certain level are eligible to receive a specified quantity of food stamps. Stamps cannot be used to purchase cigarettes, alcohol, and various other items. The government gives food retailers cash for the stamps they accept.

3-31 Figure 3.20: Food Stamp Program vs. Cash Grant Program R4 000 /P x R5 000 /P x R4 000 R

3-32 Figure 3.21: Where Food Stamps and Cash Grants Yield Different Outcomes R4 000 /P x R5 000 /P x 100 /P x R4 000 R5 000 X (units/mo) Y (R/mo)

3-33 Figure 3.22: How a health risk may alter consumer behaviour 0 I2I2 I1I1 K Diet drinks J B A Y/P d Y/P s 0 Sugared drinks I3I3 A Diet drinks B Y/P S Y/P D Sugared drinks K J I3I3 I2I2

3-34 Figure 2.23: Indifference Curves for the Utility Function U=Fs 0

3-35 Figure 2.24: Utility Along an Indifference Curve Remains Constant 0

3-36 Figure 2.25: The Optimal Bundle when U = XY, P x = 4, P y = 2, and M = 40 0