1、MicroeconomicsHal R.Varian,Chapter One,The Market,The Theory of Economics does not furnish a body of settled conclusions immediately applicable to policy. It is a method rather than a doctrine, an apparatus of the mind, a technique of thinking which helps its possessor to draw correct conclusions -

2、John Maynard Keynes,經(jīng)濟(jì)學(xué)只是一種方法和工具，而不是金科玉律 - 約翰梅納德凱恩斯,Economic Modeling經(jīng)濟(jì)模型,What causes what in economic systems?經(jīng)濟(jì)系統(tǒng)里各因素的因果關(guān)系如何？ At what level of detail shall we model an economic phenomenon?我們應(yīng)在多大細(xì)節(jié)程度上對(duì)經(jīng)濟(jì)現(xiàn)象進(jìn)行建模？ Which variables are determined outside the model (exogenous) and which are to be determi

3、ned by the model (endogenous)?哪些因素是外生變量，哪些變量是內(nèi)生變量?,Modeling the Apartment Market對(duì)公寓租賃市場(chǎng)建模,How are apartment rents determined?公寓租金是怎么決定的？ Suppose假設(shè) apartments are close or distant, but otherwise identical公寓只有遠(yuǎn)近之分，其它方面都一樣 distant apartments rents are exogenous and known遠(yuǎn)的公寓的租金是外生和已知的 many potential re

4、nters and landlords有很多潛在的承租人和出租人,Modeling the Apartment Market對(duì)公寓租賃市場(chǎng)建模,Who will rent close apartments?誰(shuí)會(huì)租靠近的公寓？ At what price?在什么價(jià)格水平下？ Will the allocation of apartments be desirable in any sense?在任何意義上講，對(duì)于公寓的分配是否有必要? How can we construct an insightful model to answer these questions?我們應(yīng)該怎樣來(lái)建立正確的模型

5、來(lái)回答這些問(wèn)題?,Economic Modeling Assumptions經(jīng)濟(jì)模型的假設(shè),Two basic postulates:兩個(gè)基本假定 Rational Choice: Each person tries to choose the best alternative available to him or her. 理性選擇: 人們總是選擇他們能支付得起的最佳消費(fèi)方式 Equilibrium: Market price adjusts until quantity demanded equals quantity supplied. 均衡: 價(jià)格會(huì)自行調(diào)整，直到人們的需求數(shù)量與供給

6、數(shù)量相等,Modeling Apartment Demand對(duì)公寓需求建模,Demand: Suppose there is one person who is willing to pay to rent a close apartment is $500/month. Then p = $500 QD = 1. 需求: 如果只有一個(gè)人愿意每月付500美元租一套房. 那么p = $500 QD = 1. Suppose the price has to drop to $490 before a 2nd person would rent. Then p = $490 QD = 2. 假設(shè)人

7、們?cè)敢庵Ц兜牡诙叩膬r(jià)格是490美元. 那么p = $490 QD = 2.,Modeling Apartment Demand對(duì)公寓需求建模,The lower is the rental rate p, the larger is the quantity of close apartments demandedp QD . 租房?jī)r(jià)格p越低，對(duì)于較近的公寓的需求量就會(huì)上升，也即p QD . The quantity demanded vs. price graph is the market demand curve for close apartments. 把需求量和市場(chǎng)價(jià)格聯(lián)系起來(lái)的

8、曲線就是較近的公寓的市場(chǎng)需求曲線.,Market Demand Curve for Apartments對(duì)于公寓的市場(chǎng)需求曲線,p,QD,Modeling Apartment Supply對(duì)公寓供給建模,Supply: It takes time to build more close apartments so in this short-run the quantity available is fixed (at say 100). 供給: 因?yàn)榻ǜ嗟妮^近的公寓需要時(shí)間，所以短期來(lái)說(shuō)，供給是固定的（比如是100）.,Market Supply Curve for Apartments公

9、寓的市場(chǎng)供給曲線,p,QS,S,Competitive Market Equilibrium競(jìng)爭(zhēng)市場(chǎng)均衡,“l(fā)ow” rental price quantity demanded of close apartments exceeds quantity available price will rise. 低的租賃價(jià)格 靠近學(xué)校的公寓的需求量超過(guò)現(xiàn)貨數(shù)量 價(jià)格上漲. “high” rental price quantity demanded less than quantity available price will fall. 高的租賃價(jià)格 需求量小于現(xiàn)貨數(shù)量 價(jià)格下降.,Competit

10、ive Market Equilibrium競(jìng)爭(zhēng)性市場(chǎng)均衡,Quantity demanded = quantity available price will neither rise nor fall 需求量 = 現(xiàn)貨數(shù)量 價(jià)格既不升也不降 so the market is at a competitive equilibrium. 因此市場(chǎng)處于競(jìng)爭(zhēng)性均衡狀態(tài).,Competitive Market Equilibrium競(jìng)爭(zhēng)性市場(chǎng)均衡,p,QD,QS,100,Competitive Market Equilibrium競(jìng)爭(zhēng)性市場(chǎng)均衡,p,QD,QS,pe,100,Competitive M

11、arket Equilibrium競(jìng)爭(zhēng)性市場(chǎng)均衡,p,QD,QS,pe,100,People willing to pay pe for close apartments get close apartments. 愿意支付pe 的價(jià)格的人租賃靠近學(xué)校的公寓.,Competitive Market Equilibrium競(jìng)爭(zhēng)性市場(chǎng)均衡,p,QD,QS,pe,100,People willing to pay pe for close apartments get close apartments. 愿意支付pe 的價(jià)格的人租賃靠近學(xué)校的公寓.,People who are not willin

12、g to pay pe for close apartments get close apartments.不愿意支付價(jià)格pe的人租賃距離學(xué)校較遠(yuǎn)的公寓.,Competitive Market Equilibrium競(jìng)爭(zhēng)性市場(chǎng)均衡,Q: Who rents the close apartments?問(wèn): 誰(shuí)租賃靠近學(xué)校的公寓? A: Those most willing to pay.答: 那些最愿意支付租金的人. Q: Who rents the distant apartments?問(wèn): 誰(shuí)租賃距離學(xué)校較遠(yuǎn)的公寓? A: Those least willing to pay.答: 那些最不

13、愿意支付租金的人. So the competitive market allocation is by “willingness-to-pay”.因此完全競(jìng)爭(zhēng)市場(chǎng)是通過(guò)支付意愿來(lái)分配公寓的.,Comparative Statics比較靜態(tài)分析,What is exogenous in the model? price of distant apartments quantity of close apartments incomes of potential renters. 模型中什么是外生變量? 距離學(xué)校較遠(yuǎn)的公寓租金價(jià)格 靠近學(xué)校公寓的數(shù)量 潛在承租人的收入. What happens

14、 if these exogenous variables change?如果這些外生變量改變會(huì)有什么結(jié)果?,Comparative Statics比較靜態(tài)分析,Suppose the price of distant apartment rises.假設(shè)距離學(xué)校較遠(yuǎn)的公寓租金價(jià)格上漲. Demand for close apartments increases (rightward shift 右移), causing a higher price for close apartments. 對(duì)于靠近學(xué)校公寓的租賃需求會(huì)上升，導(dǎo)致靠近學(xué)校的公寓的租金價(jià)格上升.,Market Equilibr

15、ium市場(chǎng)均衡,p,QD,QS,pe,100,Market Equilibrium市場(chǎng)均衡,p,QD,QS,pe,100,Higher demand需求上升,Market Equilibrium市場(chǎng)均衡,p,QD,QS,pe,100,Higher demand causes highermarket price; same quantitytraded.需求上升導(dǎo)致市場(chǎng)價(jià)格上升， 但成交量不變.,Comparative Statics比較靜態(tài)分析,Suppose there were more close apartments.假設(shè)有更多的較為靠近學(xué)校的公寓. Supply is greate

16、r, so the price for close apartments falls.供給增加, 那么 靠近學(xué)校的公寓的價(jià)格會(huì)下降.,Market Equilibrium市場(chǎng)均衡,p,QD,QS,pe,100,市場(chǎng)均衡,p,QD,QS,100,Higher supply供給增加,pe,市場(chǎng)均衡,p,QD,QS,pe,100,Higher supply causes alower market price and alarger quantity traded. 供給增加導(dǎo)致更低的市場(chǎng) 價(jià)格和更高的交易量.,Comparative Statics比較靜態(tài)分析,Suppose potential

17、renters incomes rise, increasing their willingness-to-pay for close apartments.假設(shè)潛在的租賃人的收入增加, 他們更加意愿租靠近學(xué)校的公寓. Demand rises (upward shift 上移), causing higher price for close apartments. 需求上升 (向上移動(dòng)), 導(dǎo)致靠近學(xué)校的公寓的租賃價(jià)格上升.,Market Equilibrium市場(chǎng)均衡,p,QD,QS,pe,100,市場(chǎng)均衡,p,QD,QS,pe,100,Higher incomes cause highe

18、r willingness-to-pay更高的收入導(dǎo)致租賃人更加愿意租靠近學(xué)校的公寓,市場(chǎng)均衡,p,QD,QS,pe,100,Higher incomes cause higher willingness-to-pay,higher market price, andthe same quantity traded.更高的收入導(dǎo)致租賃人更加愿意租靠近學(xué)校的公寓,更高的市場(chǎng)價(jià)格和相同的交易量.,Taxation Policy Analysis稅收政策分析,Local government taxes apartment owners. 地方政府對(duì)公寓出租人征稅. What happens to

19、price？?jī)r(jià)格如何變化？ quantity of close apartments rented?靠近學(xué)校的公寓的出租數(shù)量如何變化? Is any of the tax “passed” to renters?政府所征稅款是否回轉(zhuǎn)移給租賃人?,Taxation Policy Analysis稅收政策分析,Market supply is unaffected.市場(chǎng)供給不受影響. Market demand is unaffected.市場(chǎng)需求不受影響. So the competitive market equilibrium is unaffected by the tax.因此競(jìng)爭(zhēng)性市場(chǎng)

20、均衡不受稅收影響. Price and the quantity of close apartments rented are not changed.價(jià)格和靠近學(xué)校的公寓的出租量也不會(huì)改變. Landlords pay all of the tax.出租人支付所有稅款.,Imperfectly Competitive Markets不完全競(jìng)爭(zhēng)市場(chǎng),Amongst many possibilities are:可能情況包括: a monopolistic landlord一個(gè)壟斷的出租人 a perfectly discriminatory monopolistic landlord一個(gè)完全歧

21、視性的壟斷出租人 a competitive market subject to rent control.一個(gè)受到租金影響的競(jìng)爭(zhēng)性市場(chǎng).,A Monopolistic Landlord一個(gè)壟斷出租人,When the landlord sets a rental price p he rents D(p) apartments.當(dāng)出租人把租金價(jià)格設(shè)為p時(shí)，他能租出 D(p)套公寓. Revenue = pD(p).收益= pD(p). Revenue is low if p 0.當(dāng)p 0時(shí)收益很低 Revenue is low if p is so high that D(p) 0.當(dāng)p很高

22、時(shí)，由于 D(p) 0，收益也很低 An intermediate value for p maximizes revenue.一個(gè)居中的價(jià)格能夠最大化出租人收益.,Monopolistic Market Equilibrium壟斷市場(chǎng)均衡,p,QD,Lowprice 低價(jià),Low price, high quantity demanded, low revenue.低價(jià), 高需求量, 低收益,壟斷市場(chǎng)均衡,p,QD,Highprice 高價(jià),High price, low quantitydemanded, low revenue.高價(jià),低需求量，低收益.,壟斷市場(chǎng)均衡,p,QD,Middl

23、eprice 中間 價(jià)格,Middle price, medium quantitydemanded, larger revenue. 中間價(jià)格, 中等數(shù)量需求, 更高收益,壟斷市場(chǎng)效率,p,QD,QS,Middleprice 中間 價(jià)格,Middle price, medium quantity demanded, larger revenue. Monopolist does not rent all the close apartments.中間價(jià)格，中間數(shù)量需求，更高的收入。壟斷廠商并不出租所有的公寓,100,壟斷市場(chǎng)均衡,p,QD,QS,Middleprice 中間 價(jià)格,Middl

24、e price, medium quantity demanded, larger revenue. Monopolist does not rent all the close apartments.中間價(jià)格，中間數(shù)量需求，更高的收入。壟斷廠商并不出租所有的公寓,100,Vacant close apartments 靠近學(xué)校的空置公寓.,Perfectly Discriminatory Monopolistic Landlord完全歧視壟斷出租人,Imagine the monopolist knew everyones willingness-to-pay.假設(shè)壟斷出租人知道每一個(gè)人的租

25、賃公寓的意愿. Charge $500 to the most willing-to-pay,對(duì)最想租公寓的承租人收取$500的出租費(fèi) charge $490 to the 2nd most willing-to-pay, etc.對(duì)第二愿意租公寓的人收取 $490租金, 等等.,Discriminatory Monopolistic Market Equilibrium有歧視的壟斷市場(chǎng)均衡,p,QD,QS,100,p1 =$500,1,Discriminatory Monopolistic Market Equilibrium有歧視的壟斷市場(chǎng)均衡,p,QD,QS,100,p1 =$500,p

26、2 =$490,1,2,Discriminatory Monopolistic Market Equilibrium有歧視的壟斷市場(chǎng)均衡,p,QD,QS,100,p1 =$500,p2 =$490,1,2,p3 =$475,3,Discriminatory Monopolistic Market Equilibrium有歧視的壟斷市場(chǎng)均衡,p,QD,QS,100,p1 =$500,p2 =$490,1,2,p3 =$475,3,Discriminatory Monopolistic Market Equilibrium有歧視的壟斷市場(chǎng)均衡,p,QD,QS,100,p1 =$500,p2 =$4

27、90,1,2,p3 =$475,3,pe,Discriminatory monopolistcharges the competitive marketprice to the last renter, andrents the competitive quantityof close apartments. 有歧視的壟斷出租人對(duì)最后一個(gè) 承租人收取市場(chǎng)為競(jìng)爭(zhēng)性市場(chǎng)時(shí)的 交易價(jià)格, 并且出租當(dāng)市場(chǎng)為競(jìng)爭(zhēng) 性市場(chǎng)時(shí)的公寓出租量.,Rent Control租賃控制,Local government imposes a maximum legal price, pmax pe, the compet

28、itive price. 地方政府設(shè)定一個(gè)最高出租價(jià)格, pmax pe,競(jìng)爭(zhēng)性市場(chǎng)價(jià)格.,Market Equilibrium市場(chǎng)均衡,p,QD,QS,pe,100,Market Equilibrium市場(chǎng)均衡,p,QD,QS,pe,100,pmax,Market Equilibrium市場(chǎng)均衡,p,QD,QS,pe,100,pmax,Excess demand額外需求,市場(chǎng)均衡,p,QD,QS,pe,100,pmax,Excess demand過(guò)度需求,The 100 close apartments are no longer allocated by willingness-to-pa

29、y (lottery, lines, large families first?). 100套靠近學(xué)校的公寓不在依據(jù)承租人的意愿來(lái)分配 (律師,大家庭優(yōu)先?).,Which Market Outcomes Are Desirable?哪個(gè)市場(chǎng)的結(jié)果是可取的,Which is better? Rent control Perfect competition Monopoly Discriminatory monopoly 哪個(gè)更好哦? 租賃控制 完全競(jìng)爭(zhēng)市場(chǎng) 壟斷 歧視性壟斷,Pareto Efficiency帕累托效率,Vilfredo Pareto; 1848-1923. 維爾弗雷多帕累托

30、; 1848-1923. A Pareto outcome allows no “wasted welfare”;帕雷托結(jié)果不允許存在福利的浪費(fèi) ; i.e. the only way one persons welfare can be improved is to lower another persons welfare. 唯一能改善一個(gè)人福利的方法是降低其他人的福利.,Pareto Efficiency帕累托效率,Jill has an apartment; Jack does not.吉爾有一套公寓; 杰克沒(méi)有. Jill values the apartment at $200;

31、Jack would pay $400 for it.吉爾為了租一套公寓愿意支付$200，但杰克愿意支付$400. Jill could sublet the apartment to Jack for $300.吉爾可以以$300的價(jià)格轉(zhuǎn)租給杰克. Both gain, so it was Pareto inefficient for Jill to have the apartment.同樣, 因此對(duì)于吉爾來(lái)說(shuō)是帕累托無(wú)效的.,Pareto Efficiency帕累托效率,A Pareto inefficient outcome means there remain unrealized

32、mutual gains-to-trade.帕累托無(wú)效意味著存在沒(méi)有實(shí)現(xiàn)的互惠交易. Any market outcome that achieves all possible gains-to-trade must be Pareto efficient.任何完成了所有可能互惠交易的市場(chǎng)都是帕累托有效的.,Pareto Efficiency帕累托效率,Competitive equilibrium:競(jìng)爭(zhēng)均衡: all close apartment renters value them at the market price pe or more所有承租人對(duì)于靠近學(xué)校的公寓的租金估價(jià)為市場(chǎng)價(jià)pe或者更高 all others value close apartments at less than pe所有其他人對(duì)于靠近學(xué)校公寓的租金估價(jià)至少為 pe so no mutually beneficial trades remain因此沒(méi)有相互互惠的交易產(chǎn)生 so the outcome is Pareto efficient. 因此結(jié)果是帕累托有效的.,Pareto Efficiency帕累托