2、ionPuzzleCYConsumptionfunctionfromlongtimeseriesdata(constantAPC)Consumptionfunctionfromcross-sectionalhouseholddata(fallingAPC)5費(fèi)雪的代際選擇假設(shè)消費(fèi)者具有遠(yuǎn)見(jiàn)，并在現(xiàn)在和將來(lái)消費(fèi)之間進(jìn)行選擇以期使其一生的滿足感達(dá)到最大。于是消費(fèi)者的消費(fèi)就受制于代際預(yù)算約束，即現(xiàn)在和將來(lái)可以獲得的所有經(jīng)濟(jì)資源。圖PP7。邊際替代率和最優(yōu)化：圖PP8-10凱恩斯認(rèn)為當(dāng)前收入決定當(dāng)前消費(fèi)；費(fèi)雪則認(rèn)為當(dāng)前消費(fèi)取決于一生收入的現(xiàn)值，收入發(fā)生在何時(shí)無(wú)關(guān)緊要，因?yàn)橄M(fèi)者可
3、以實(shí)行跨期借貸。6Thebudgetconstraintshowsallcombinations ofC1andC2thatjustexhausttheconsumer’sresources.代際預(yù)算約束C1C2Y1Y2BorrowingSavingConsump=incomeinbothperiods7Marginalrateofsubstitution(MRS):theamountofC2consumerwouldbewillingtosubstituteforoneunitofC1.ConsumerpreferencesC1C2IC1Theslopeofanindi
4、fferencecurveatanypointequalstheMRSatthatpoint.1MRS8Theoptimal(C1,C2)iswherethebudgetlinejusttouchesthehighestindifferencecurve.OptimizationC1C2OAttheoptimalpoint,MRS=1+r9AnincreaseinY1orY2shiftsthebudgetlineoutward.HowCrespondstochangesinYC1C2Results: Providedtheyarebothnormalgoods,C1and
5、C2bothincrease,…regardlessofwhethertheincomeincreaseoccursinperiod1orperiod2.10費(fèi)雪的代際選擇消費(fèi)與真實(shí)利率r圖PP11。收入效應(yīng)、替代效應(yīng)。真實(shí)利率上升，兩種效應(yīng)都使C2增加，C1增減則取決于哪一個(gè)效應(yīng)更大。借入約束使最優(yōu)化無(wú)法實(shí)現(xiàn)：圖PP1211AAnincreaseinrpivotsthebudgetlinearoundthe point(Y1,Y2).HowCrespondstochangesinrC1C2Y1Y2ABAsdepictedhere,C1fallsandC2rises.Ho
6、wever,itcouldturnoutdifferently…12TheoptimalchoiceisatpointD.Butsincetheconsumercannotborrow,thebesthecandoispointE.ConsumeroptimizationwhentheborrowingconstraintisbindingC1C2Y1DE13莫迪利亞尼的生命周期假說(shuō)消費(fèi)者的收入水平隨生命周期而變動(dòng)，儲(chǔ)蓄是消費(fèi)者實(shí)現(xiàn)平滑消費(fèi)的手段。C=(W+RY)/T或C=aW+βY-a=(1/T)對(duì)初始財(cái)產(chǎn)的邊際消費(fèi)傾向；β=(R/T)對(duì)收入的邊際消費(fèi)傾向。LCY能夠解
7、釋消費(fèi)悖論：C/Y=a(W/Y)+β，對(duì)家庭而言，初始財(cái)富并不象收入那樣變動(dòng)頻繁，因此高收入家庭會(huì)比低收入家庭APC為低；而就長(zhǎng)期尺度而言，W和Y共同增長(zhǎng)，使得C/Y大致恒定。LCY的儲(chǔ)蓄變動(dòng)狀況圖：PP1514生命周期假說(shuō)的含義TheLCHimpliesthatsavingvariessystematicallyoveraperson’slifetime.SavingDissavingRetirement beginsEnd oflifeConsumptionIncome$Wealth15弗里德曼的恒久收入假說(shuō)當(dāng)前收入可分為
