1、第1章 市场 1、经济学的概念与方法 建立模型：经济学的研究是通过对社会各种现象建立模型来进行的。通过一个模型可以简单地表示现实世界的情况。变量设计与因果关联、对问题的简化 构建经济模型的五个步骤 A 界定问题及其范围（Definition of the Problem）B 形成假说（Formulation of Hypotheses）C 根据假说对现实做出解释（Explanation）D 对经济模型进行检验（Verification）E 根据检验结果放弃、修改或者接受模型（Conclusion）最优化与均衡 每当我们试图分析人类的行为时，我们需要一种分析的基础框架，这个基础框架建立在以下两个
2、简单原理的基础上：最优化：人们总是选择他们能支付得起的最佳消费方式（厂商总是选择成本最低的生产方式）。均衡原理：价格会自动调整，直到人们的需求数量与供给数量相等。2、需求曲线：收入水平约束下消费者为某一数量的消费水平愿意支付的最高价格。这个价格我们也称其为保留价格。（Reservation Price）QP需求的区域0 或者说需求曲线显示的是在非价格因素保持不变的情况下，每单位产品售价发生的变化导致他愿意购买的数量的变化（价格数量关系）；它与价格成反向相关关系。非价格的需求决定因素包括：收入消费者偏好相关商品价格（互补品、替代品）3、供给曲线：生产者在成本约束下提供特定数量的产品所能接受的最低
3、价格。供给的区域短期的特例：土地或住房供给一般化的供给线 4.市场均衡：均衡价格与均衡数量的决定sLssDP*市场调节（价格机制市场调节（价格机制）当当PPe时，时，QdQs，市场出现，市场出现超额供给超额供给，消费者主导，买方市场消费者主导，买方市场.P自动下降，自动下降，过过剩剩逐渐减小，直至均衡；逐渐减小，直至均衡；当当PQs，市场出现，市场出现超额需求超额需求，供给者主导，卖方市场供给者主导，卖方市场.P自动上升，自动上升，短短缺缺逐渐减小，直至均衡。逐渐减小，直至均衡。市场均衡的变动市场均衡的变动 当需求曲线和供给曲线移动时，均衡价格和均当需求曲线和供给曲线移动时，均衡价格和均衡产量
4、都会发生变动。衡产量都会发生变动。分析均衡变动的三个步骤：分析均衡变动的三个步骤：（1）确定该变动是需求曲线还是供给曲线；）确定该变动是需求曲线还是供给曲线；（2）确定曲线移动的方向；）确定曲线移动的方向；（3）用供求图说明均衡变动的影响。）用供求图说明均衡变动的影响。比较静态分析SDS1可交易领域扩大可交易的领域 比较静态分析SDS1可交易领域扩大可交易的领域可交易领域的进一步扩大 不完全竞争的市场 完全（差别）垄断的状态：厂商将商品按照不同的价格分别卖给不同的消费者，最终的商品交易量正好与完全竞争市场完成的交易量是相同的，只是生产者剥夺了所有的消费者剩余。P*P1P2差别垄断者：短期供给情
5、况下的均衡(S曲线垂直)QP0差别垄断市场的交易过程：长期供给 一般垄断者：交易的数量会低于完全竞争市场的交易量，存在厂商对消费者剩余的剥夺。QP0一般垄断市场的交易过程：垄断者按照相同的价格出售产品P0Q0Q1P1An Illustration:Modeling the Apartment Market Purpose:How are apartment rents determined?Are rents“desirable”?Simplifying assumptions:apartments are close or distant,but otherwise identical di
6、stant apartments rents are exogenous (外生变量）and known many potential renters and landlordsTwo Very Common Modeling Assumptions Rational Choice(理性选择）:Each person tries to choose the best alternative available to him or her.Equilibrium（均衡）:economic agents interact with each other,resulting in an equili
7、brium,in which each person reaches an optimal decision given others decisions.Modeling Apartment Demand Demand:Suppose the most any one person is willing to pay to rent a close apartment is$500/month.Then p=$500 QD=1.Suppose the price has to drop to$490 before a 2nd person would rent.Then p=$490 QD=
8、2.Modeling Apartment Demand The lower is the rental rate p,the larger is the quantity of close apartments demandedp QD.The quantity demanded vs.price graph is the market demand curve for close apartments.Market Demand Curve for ApartmentspQDModeling Apartment Supply Supply:It takes time to build mor
9、e close apartments,so in this short-run the quantity available is fixed(at say 100).Market Supply Curve for ApartmentspQS100Competitive Market Equilibrium(竞争性市场均衡）Quantity demanded=quantity available price will neither rise nor fall so the market is at a competitive equilibrium.Competitive Market Eq
10、uilibriumpQD,QSpe100People willing to pay pe for close apartments get closeapartments.People not willing to pay pe for close apartments get distant apartments.Comparative Statics（比较静态分析）What is exogenous in the model?price of distant apartments quantity of close apartments incomes of potential rente
11、rs.What happens if these exogenous variables change?Note：We are not analyzing the transition process or dynamic process.Comparative Statics Suppose the price of distant apartment rises.Demand for close apartments increases(rightward shift),causing a higher price for close apartments.Market Equilibri
12、umpQD,QSpe100Higher demand causes highermarket price;same quantitytraded.More Comparative Statics(Do Them Yourself)Suppose there were more close apartments.Or,renters income rises;Elaboration of the Basic Model:Taxation Policy Analysis Local government taxes apartment owners.What happens to price qu
13、antity of close apartments rented?Is any of the tax“passed”to renters?Taxation Policy Analysis Market supply is unaffected.Market demand is unaffected.So the competitive market equilibrium is unaffected by the tax.Price and the quantity of close apartments rented are not changed.Landlords pay all of
14、 the tax.Imperfectly Competitive MarketCase 1：A Monopolistic Landlord Landlord sets a rental price p he rents D(p)apartments.Revenue=pD(p).He chooses p to maximizes p D(p),subject to D(p)S(total number of apartments in his hands)Typically,his optimal p is such thatD(p)S,that is,there are vacant apar
15、tments.Monopolistic Market EquilibriumpQD,QSMiddlepriceMiddle price,medium quantitydemanded,larger revenue.Monopolist does not rent all theclose apartments.100Vacant close apartments.Imperfectly Competitive Market Case 2：Perfectly Discriminatory Monopolistic Landlord Imagine the monopolist knew will
16、ingness-to-pay of everybody,Charge$500 to the most willing-to-pay,charge$490 to the 2nd most willing-to-pay,etc.Discriminatory Monopolistic Market EquilibriumpQD,QS100p1=$5001Discriminatory Monopolistic Market EquilibriumpQD,QS100p1=$500p2=$49012Discriminatory Monopolistic Market EquilibriumpQD,QS10
17、0p1=$500p2=$49012p3=$4753Discriminatory Monopolistic Market EquilibriumpQD,QS100p1=$500p2=$49012p3=$4753Discriminatory Monopolistic Market EquilibriumpQD,QS100p1=$500p2=$49012p3=$4753peDiscriminatory monopolistcharges the competitive marketprice to the last renter,andrents the competitive quantityof
18、 close apartments.Rent Control(房租管制）Local government imposes a maximum legal price,pmax p2x1x20预算约束线：p1p2m/p1m/p2完全互补情况下的最优选择情况下的最优选择AC非最优选择最优选择221121122211212121lnlnln),(pmdcdxpmdccxppdxcxmxpxpxdxcuxxxxudc1221121122112211,)(txRmxpxtpxxxmxpxtpmxpxp收入，政府通过增税获得的）（）的消费束，满足的结果是消费者选择（的消费，最优化选择少消费者无论增加还是减x1x2X2*X1*0原预算线斜率为-p1/p2含数量税的预算线斜率为-(p1+t)/p2含所得税的最优选择含数量税的最优选择右边的无差异曲线上。个点落在的方法实现最优化。这换取可以通过用减少，率等于最优化的点，预算线斜）并不是）的直线。但是点（线斜率相同并经过新的预算线是与原预算12212121122112211/,xxppxxxxtxmxpxpRmxpxp
