【正文】 tion only if they are unanticipated. slide 42 CHAPTER 16 Consumption The Psychology of Instant Gratification ? Theories from Fisher to Hall assume that consumers are rational and act to maximize lifetime ，按照終生效用最大化來采取行動。 ? PIH: current ine is subject to random, transitory fluctuations. 現期收入會容易出現隨機的，暫時性的波動。 slide 34 CHAPTER 16 Consumption The Permanent Ine Hypothesis ? due to Milton Friedman (1957) ? Y = Y P + Y T where Y = current ine Y P = permanent ine average ine, which people expect to persist into the future Y T = transitory ine temporary deviations from average ine slide 35 CHAPTER 16 Consumption The Permanent Ine Hypothesis ? 消費者面對收入暫時波動時，會使用儲蓄和借款來平穩(wěn)消費 Consumers use saving amp。 Across households, ine varies more than wealth, so highine households should have a lower APC than lowine households. ?在長期里，總財富和收入同時增長， APC穩(wěn)定。 ? 宣布未來減稅 ?意味著未來時期的可分配收入增加。 …and her consumption may behave as in the Keynesian theory even though she is rational amp。 substitution effects. 也許，利息率對當期的消費根本沒有影響。 ? Fisher: 當期的消費僅取決于終生收入的現值，由于消費者可以跨期借貸，獲得收入的時間是無關緊要的。 ? 消費者選擇受到 an intertemporal budget constraint, 為當期和未來消費提供所有資源的衡量尺度。slide 0 CHAPTER 16 Consumption ?consumption slide 1 CHAPTER 16 Consumption 在本章，你將學到以下內容 … 最經典消費理論的介紹 , 包括 : ? John Maynard Keynes: consumption and current ine ? Irving Fisher: intertemporal choice ? Franco Modigliani: the lifecycle hypothesis ? Milton Friedman: the permanent ine hypothesis ? Robert Hall: the randomwalk hypothesis ? David Laibson: the pull of instant gratification slide 2 CHAPTER 16 Consumption Keynes’s conjectures 1. 0 MPC 1 2. Average propensity to consume (APC ) falls as ine rises. (APC = C/Y ) 3. 收入是消費的主要決定因素。 slide 7 CHAPTER 16 Consumption The Consumption Puzzle C Y Consumption function from long time series data (constant APC ) Consumption function from crosssectional household data (falling APC ) slide 8 CHAPTER 16 Consumption Irving Fisher and Intertemporal Choice ? 許多關于消費理論工作的基礎 . ? 假定消費者是 forwardlooking 并且選擇當期和未來時期的消費來最大化終生效用。 slide 15 CHAPTER 16 Consumption Consumer preferences Marginal rate of substitution (MRS ): 消費者愿意用多少單位的 C2 來替換一個單位的 C1. C1 C2 IC1 The slope of an indifference curve at any point equals the MRS at that point. 1 MRS slide 16 CHAPTER 16 Consumption Optimization 最優(yōu)的 (C1,C2) 組合是 the budget line just touches the highest indifference curve. C1 C2 O At the optimal point, MRS = 1+r slide 17 CHAPTER 16 Consumption How C responds to changes in Y Y1 or Y2 的增加shifts the budget line outward. C1 C2 結果 : 假設 C1 and C2 都是正常品， C1 and C2 both increase, … 無論收入增加時發(fā)生在 in period 1 or pe