微观经济学现代观点英文chapterPPT课件

ChapterTwoBudgetConstraint预算约束StructureDescribebudgetconstraintAlgebraGraphDescribechangesinbudgetconstraintGovernmentprogramsandbudgetconstraintsNon-linearbudgetlinesConsumptionSetsAconsumptionset（消费集）isthecollectionofallphysicallypossibleconsumptionbundles（消费束）totheconsumer.ConsumptionBundleAconsumptionbundlecontainingx1unitsofcommodity1,x2unitsofcommodity2andsoonuptoxnunitsofcommoditynisdenotedbythevector(x1,x2,…,xn).PhysicalConstraintsNon-negative:Consumptionset:X={(x1,…,xn)|x1³0,…,xn³0}Youonlyhave24hoursadaySubsistenceneedEtc.BudgetConstraintWhatconstrainsconsumptionchoice?Budgetarytimeotherresourcelimitations.BudgetConstraintsCommoditypricesarep1,p2,…,pn.Q:Whenisabundle(x1,…,xn)affordableatpricesp1,…,pn?A:Whenp1x1+…+pnxn£mwheremistheconsumer’s(disposable)income.BudgetConstraintsThebundlesthatareonlyjustaffordableformtheconsumer’sbudgetconstraint.Thisistheset{(x1,…,xn)|x1³0,…,xn³0andp1x1+…+pnxn=m}.BudgetConstraintsTheconsumer’sbudgetset（预算集）isthesetofallaffordablebundles;B(p1,…,pn,m)={(x1,…,xn)|x1³0,…,xn³0andp1x1+…+pnxn£m}Thebudgetconstraintistheupperboundaryofthebudgetset.BudgetSetandConstraintforTwoCommoditiesx2x1Budgetconstraintisp1x1+p2x2=m.m/p1m/p2BudgetSetandConstraintforTwoCommoditiesx2x1Budgetconstraintisp1x1+p2x2=m.m/p2m/p1BudgetSetandConstraintforTwoCommoditiesx2x1Budgetconstraintisp1x1+p2x2=m.m/p1Justaffordablem/p2BudgetSetandConstraintforTwoCommoditiesx2x1Budgetconstraintisp1x1+p2x2=m.m/p1JustaffordableNotaffordablem/p2BudgetSetandConstraintforTwoCommoditiesx2x1Budgetconstraintisp1x1+p2x2=m.m/p1AffordableJustaffordableNotaffordablem/p2BudgetSetandConstraintforTwoCommoditiesx2x1Budgetconstraintisp1x1+p2x2=m.m/p1BudgetSetthecollectionofallaffordablebundles.m/p2BudgetSetandConstraintforTwoCommoditiesx2x1p1x1+p2x2=misx2=-(p1/p2)x1+m/p2soslopeis-p1/p2.m/p1BudgetSetm/p2MeaningoftheSlopeIncreasingx1by1mustreducex2byp1/p2.Opportunitycostofconsumingx1Or,therateofexchangethatmarketallows.BudgetConstraintsx2x1Slopeis-p1/p2+1-p1/p2BudgetConstraintsx2x1+1-p1/p2Opp.costofanextraunitofcommodity1isp1/p2unitsforegoneofcommodity2.BudgetConstraintsx2x1Opp.costofanextraunitofcommodity1isp1/p2unitsforegoneofcommodity2.Opp.costofanextraunitofcommodity2isp2/p1unitsforegoneofcommodity1.-p2/p1+1BudgetSets&Constraints;IncomeandPriceChangesThebudgetconstraintandbudgetsetdependuponpricesandincome.Whathappensaspricesorincomechange?Howdothebudgetsetandbudgetconstraintchangeasincomemincreases?Originalbudgetsetx2x1HigherincomegivesmorechoiceOriginalbudgetsetNewaffordableconsumptionchoicesx2x1Originalandnewbudgetconstraintsareparallel(sameslope).Howdothebudgetsetandbudgetconstraintchangeasincomemdecreases?Originalbudgetsetx2x1Howdothebudgetsetandbudgetconstraintchangeasincomemdecreases?x2x1New,smallerbudgetsetConsumptionbundlesthatarenolongeraffordable.Oldandnewconstraintsareparallel.BudgetConstraints-IncomeChangesIncreasesinincomemshifttheconstraintoutwardinaparallelmanner,therebyenlargingthebudgetsetandimprovingchoice.Decreasesinincomemshifttheconstraintinwardinaparallelmanner,therebyshrinkingthebudgetsetandreducingchoice.BudgetConstraints-IncomeChangesNooriginalchoiceislostandnewchoicesareaddedwhenincomeincreases,sohigherincomecannotmakeaconsumerworseoff.Anincomedecreasemay(typicallywill)maketheconsumerworseoff.BudgetConstraints-PriceChangesWhathappensifjustonepricedecreases?Supposep1decreases.Howdothebudgetsetandbudgetconstraintchangeasp1decreasesfromp1’top1”?Originalbudgetsetx2x1m/p2m/p1’m/p1”-p1’/p2Howdothebudgetsetandbudgetconstraintchangeasp1decreasesfromp1’top1”?Originalbudgetsetx2x1m/p2m/p1’m/p1”Newaffordablechoices-p1’/p2Howdothebudgetsetandbudgetconstraintchangeasp1decreasesfromp1’top1”?Originalbudgetsetx2x1m/p2m/p1’m/p1”NewaffordablechoicesBudgetconstraintpivots;slopeflattensfrom-p1’/p2to-p1”/p2-p1’/p2-p1”/p2BudgetConstraints-PriceChangesReducingthepriceofonecommoditypivotstheconstraintoutward.Nooldchoiceislostandnewchoicesareadded,soreducingonepricecannotmaketheconsumerworseoff.BudgetConstraints-PriceChangesSimilarly,increasingonepricepivotstheconstraintinwards,reduceschoiceandmay(typicallywill)maketheconsumerworseoff.UniformAdValoremSalesTaxesAnadvaloremsalestax（从价营业税）leviedatarateof5%increasesallpricesby5%,frompto(1+0.05)p=1.05p.Anadvaloremsalestaxleviedatarateoftincreasesallpricesbytpfrompto(1+t)p.Auniformsalestaxisapplieduniformlytoallcommodities.UniformAdValoremSalesTaxesAuniformsalestaxleviedatratetchangestheconstraintfromp1x1+p2x2=mto(1+t)p1x1+(1+t)p2x2=mUniformAdValoremSalesTaxesAuniformsalestaxleviedatratetchangestheconstraintfromp1x1+p2x2=mto(1+t)p1x1+(1+t)p2x2=mi.e.p1x1+p2x2=m/(1+t).UniformAdValoremSalesTaxesx2x1p1x1+p2x2=mp1x1+p2x2=m/(1+t)UniformAdValoremSalesTaxesx2x1EquivalentincomelossisUniformAdValoremSalesTaxesx2x1AuniformadvaloremsalestaxleviedatratetisequivalenttoanincometaxleviedatrateTheFoodStampProgramFoodstampsarecouponsthatcanbelegallyexchangedonlyforfood.Howdoesacommodity-specificgiftsuchasafoodstampalterafamily’sbudgetconstraint?TheFoodStampProgramSupposem=$100,pF=$1andthepriceof“othergoods”ispG=$1.“Othergoods”isacompositegood(复合商品)Itsimplifiestheanalysistoa2-goodmodel.ThebudgetconstraintisthenF+G=100.TheFoodStampProgramGF100100F+G=100:beforestamps.TheFoodStampProgramF+G=100:beforestamps.Budgetsetafter40foodstampsissued.GF10010014040(F-40)+G=100forF40G=100forF<40TheFoodStampProgramGF100100F+G=100:beforestamps.Budgetsetafter40foodstampsissued.140Thefamily’sbudgetsetisenlarged.40(F-40)+G=100forF40G=100forF<40TheFoodStampProgramWhatiffoodstampscanbetradedonablackmarketfor$0.50each?F+G=100+0.5(40-F)forF<40(F-40)+G=100forF40TheFoodStampProgramGF100100F+G=100:beforestamps.Budgetconstraintafter40foodstampsissued.140120Budgetconstraintwithblackmarkettrading.40F+G=100+0.5(40-F)forF<40(F-40)+G=100forF40TheFoodStampProgramGF100100F+G=100:beforestamps.Budgetconstraintafter40foodstampsissued.140120Blackmarkettradingmakesthebudgetsetlargeragain.40BudgetConstraints-RelativePrices“Numeraire”(记价物)means“unitofaccount”.Thebudgetlinep1x1+p2x2=mCanbeequivalentlyexpressedasSettingp2=1makescommodity2thenumeraireanddefinesallpricesrelativetop2;BudgetConstraints-RelativePricesAnycommoditycanbechosenasthenumerairewithoutchangingthebudgetsetorthebudgetconstraint.Arelativepriceistheratesofexchangeofcommodities2forunitsofcommodity1.ShapesofBudgetConstraintsQ:Whatmakesabudgetconstraintastraightline?A:Astraightlinehasaconstantslopeandtheconstraintisp1x1+…+pnxn=msoifpricesareconstantsthenaconstraintisastraightline.ShapesofBudgetConstraintsButwhatifpricesarenotconstants?E.g.bulkbuyingdiscounts,orpricepenaltiesforbuying“toomuch”.Thenconstraintswillbecurved.ShapesofBudgetConstraints-QuantityDiscountsSupposep2isconstantat$1butthatp1=$2for0£x1£20andp1=$1forx1>20.ShapesofBudgetConstraints-QuantityDiscountsSupposep2isconstantat$1butthatp1=$2for0£x1£20andp1=$1forx1>20.Thentheconstraint’sslopeis-2,for0£x1£20-p1/p2=-1,forx1>20{ShapesofBudgetConstraintswithaQuantityDiscountm=$1005010020Slope=-2/1=-2(p1=2,p2=1)Slope=-1/1=-1(p1=1,p2=1)80x2x1ShapesofBudgetConstraintswithaQuantityDiscountm=$1005010020Slope=-2/1=-2(p1=2,p2=1)Slope=-1/1=-1(p1=1,p2=1)80x2x1BudgetConstraintswithaQuantityDiscountTheconstraintis2x1+x2=mfor0£x1£20220+(x1-20)+x2=mforx1>20{ShapesofBudgetConstraintswithaQuantityDiscountm=$100501002080x2x1BudgetSetBudgetConstraintShapesofBudgetConstraintswithaQuantityPenaltyx2x1BudgetSetBudgetConstraintShapesofBudgetConstraints-OnePriceNegativeCommodity1isstinkygarbage.Youarepaid$2perunittoacceptit;i.e.p1=-$2.p2=$1.Income,otherthanfromacceptingcommodity1,ism=$10.Thentheconstraintis-2x1+x2=10orx2=2x1+10.ShapesofBudgetConstraints-OnePriceNegative10Budgetconstraint’sslopeis-p1/p2=-(-2)/1=+2x2x1x2=2x1+10ShapesofBudgetConstraints-OnePriceNegative10x2x1Budgetsetisallbundlesforwhichx1³0,x2³0andx2£2x1+10.