1、The Markets for “Lemons”: Quality uncertainty and The Market Mechanism檸檬市場：質(zhì)量的不確定性和市場機制Geogre A. Akerlof 阿克洛夫一、引言This paper relates quality and uncertainty. The existence of goods of many grades poses interesting and important problems for the theory of markets.（本文論述的是質(zhì)量和不確定性問題?，F(xiàn)實中存在大量多種檔次的物品給市場理論提出

2、了饒有趣味而十分重大的難題）On the one hand, the interaction of quality differences and uncertainty may explain important institutions of the labor market.（一方面，質(zhì)量差異和不確定性的相互作用可以解釋勞動力的重要機制）On the other hand, this paper presents a struggling attempt to give structure to the statement: Business in under-developed cou

3、ntries is difficult; in particular, a structure is given for determining the economic costs of dishonesty.（另一方面，本文試圖通過討論獲得這樣的結(jié)論：在不發(fā)達國家，商業(yè)交易是困難的，其中，特別論及了欺騙性交易的經(jīng)濟成本）Additional applications of the theory include comments on the structure of money markets, on the notion of insurability, on the liquidity

4、 of durables, and on brand-name goods.（本文的理論還可以用來研究貨幣市場、保險可行性、耐用品的流動性和名牌商品等問題）There are many markets in which buyers use some market statistic to judge the quality of prospective purchases.（在許多市場中，買者利用市場的統(tǒng)計數(shù)據(jù)來判斷他們將要購買的商品的質(zhì)量）In this case there is incentive for sellers to market poor quality merchandi

5、se, since the returns for good quality accrue mainly to the entire group whose statistic is affected rather than to the individual seller. As a result there tends to be a reduction in the average quality of goods and also in the size of the market.（在這種情況下，賣者有動力提供低質(zhì)量商品，因為某種商品的價格主要取決于所有同類商品質(zhì)量的統(tǒng)計數(shù)據(jù)而非該商

6、品的實際質(zhì)量。結(jié)果，商品的平均質(zhì)量將趨于下降，市場規(guī)模將不斷縮?。㊣t should also be perceived that in these markets social and private returns differ, and therefore, in some cases, governmental intervention may increase the welfare of all parties. Or private institutions may arise to take advantage of the potential increases in wel

7、fare which can accrue to all parties.（我們還可以觀察到在這種市場上，對個人和社會有不同的回報，因此，某種情況下，政府的干預(yù)可以增進社會的總體福利水平?；蛘哒f，私人組織利用了整個社會福利水平潛在的增長機會而使自己獲利）By nature, however, these institutions are nonatomistic, and therefore concentrations of power- with ill consequences of their own-can develop.（實際上，這些私人組織的行動所產(chǎn)生的影響并非可以忽略不計，因

8、此，盡管集權(quán)本身有許多負面影響，但是，一定程度上的集權(quán)可以保證經(jīng)濟的健康發(fā)展）The automobile market is used as a finger exercise to illustrate and develop these thoughts. It should be emphasized that this market is chosen for its concreteness and ease in understanding rather than for its importance or realism.（下面，我們用汽車市場作為例子來闡釋和進一步發(fā)展以上的思

9、想。需要指出的是，之所以選擇舊車市場來討論，是因為這個例子很具體，并且容易理解，而不是因為它的重要性和有何現(xiàn)實意義）二、以汽車市場模型為例（一）汽車市場The example of used cars captures the essence of the problem. From time to time one hears either mention of or surprise at the large price difference between new cars and those which have just left the showroom. The usual lu

10、nch table justification for this phenomenon is the pure joy of owning a new car.（舊車市場的例子可以抓住問題的本質(zhì)。人們不止一次的聽說或驚訝于新車與剛剛開出樣品陳列室的汽車之間的價格存在巨大差別。對于這種情況最普遍的解釋是人們有一種對“新”車的特別偏好）We offer a different explanation. Suppose (for the sake of clarity rather than reality) that there are just four kinds of cars. There

11、 are new cars and used cars. There are good cars and bad cars (which in America are known as lemons). A new car may be a good car or a lemon, and of course the same is true of used cars.（假設(shè)（作出這種假設(shè)只是為了簡化分析，而非從實際出發(fā)）用四種汽車：新車和舊車；高質(zhì)量的車和低質(zhì)量的車（低質(zhì)量的車在美國被稱為“檸檬”）。一輛新車可能是高質(zhì)量的，也可能是“檸檬”，當(dāng)然一輛舊車也同樣有兩種情況）The indivi

12、duals in this market buy a new automobile without knowing whether the car they buy will be good or a lemon. But they do know that with probability q it is a good car and with probability (1-q) it is a lemon; by assumption, q is the proportion of good cars produced and (1 - q) is the proportion of le

13、mons.（在這樣的市場上，消費者買新車時并不知道車輛到底是高質(zhì)量的還是“檸檬”，但是他知道這輛車是高質(zhì)量的概率是q，是“檸檬”的概率是“1-q”。這里假設(shè)q是高質(zhì)量車占所有汽車的比率，1-q是“檸檬”的比率）After owning a specific car, however, for a length of time, the car owner can form a good idea of the quality of this machine; i.e., the owner assigns a new probability to the event that his car

14、is a lemon. This estimate is more accurate than the original estimate.（車主在擁有汽車后一段時間內(nèi)就會了解到該車的質(zhì)量，也就是說，此時車主可以賦予該車可能是“檸檬”的一個概率值，這個估計比初始的估計更加準確）An asymmetry in available information has developed: for the sellers now have more knowledge about the quality of a car than the buyers. But good cars and bad ca

15、rs must still sell at the same price- since it is impossible for a buyer to tell the difference between a good car and a bad car.（于是，信息不對稱發(fā)生了：賣主掌握了比買主更多的關(guān)于汽車質(zhì)量的信息。對于買主來說，由于他不能在買車時區(qū)分汽車的質(zhì)量，所以，高質(zhì)量車和低質(zhì)量車只能以同一個價格水平出售）It is apparent that a used car can-not have the same valuation as a new car - if it did

16、have the same valuation, it would clearly be advantageous to trade a lemon at the price of new car, and buy another new car, at a higher prob-ability q of being good and a lower probability of being bad.（顯然，一輛新車和一輛舊車不應(yīng)該有相同的評價。如果他們擁有相同的評價，車主通過以高質(zhì)量車的價格出售“檸檬”后再買一輛新車，該新車是高質(zhì)量的概率q大于原先購買新車的概率）Thus the owne

17、r of a good machine must be locked in. Not only is it true that he cannot receive the true value of his car, but he cannot even obtain the expected value of a new car.（這樣，高質(zhì)量車的擁有者將不會賣出汽車，因為如果賣出汽車他不僅無法得到汽車的真實價值，也無法獲得一輛新車的期望價值）Greshams law has made a modified reappearance. For most cars traded will be

18、 the lemons, and good cars may not be traded at all. The bad cars tend to drive out the good (in much the same way that bad money drives out the good).（這里出現(xiàn)了一個修正后的格萊欣定律。當(dāng)“檸檬”充斥汽車市場時，高質(zhì)量車根本不會成交，于是，如同劣幣驅(qū)逐良幣一樣，低質(zhì)量車將高質(zhì)量車逐出市場）But the analogy with Greshams law is not quite complete: bad cars drive out the

19、 good because they sell at the same price as good cars; similarly, bad money drives out good because the exchange rate is even.（然而，該結(jié)果與格萊欣定律并不完全一樣：低質(zhì)量車驅(qū)逐高質(zhì)量車是因為低質(zhì)量車和高質(zhì)量車在相同的價格水平上出售。相似地，劣幣驅(qū)逐良幣是因為兩者的交換利率相同）But the bad cars sell at the same price as good cars since it is impossible for a buyer to tell

20、the difference between a good and a bad car; only the seller knows. In Greshams law, however, presumably both buyer and seller can tell the difference between good and bad money. So the analogy is instructive, but not complete.（但是低質(zhì)量車之所以與高質(zhì)量以同一個價格出售是因為買主無法區(qū)分一輛車到底是低質(zhì)量的還是高質(zhì)量的，這只有賣主才知道的信息。在格萊欣定律中，買主和賣主

21、大概否可以區(qū)分劣幣和良幣。所以說，這個類比具有啟發(fā)性，但非完全相同）（二）非對稱信息It has been seen that the good cars may be driven out of the market by the lemons. But in a more continuous case with different grades of goods, even worse pathologies can exist.（我們已經(jīng)看到質(zhì)量好的汽車會被“檸檬”逐出市場。但是，在不同質(zhì)量等級的產(chǎn)品連續(xù)分布的情形下，更糟糕的情況也會發(fā)生）For it is quite possibl

22、e to have the bad driving out the not-so-bad driving out the medium driving out the not-so-good driving out the good in such a sequence of events that no market exists at all.（質(zhì)量最差的汽車在將質(zhì)量最好的汽車逐出市場后，會繼續(xù)將質(zhì)量較好、質(zhì)量中等和質(zhì)量稍差的汽車依次逐出市場，從而導(dǎo)致二手車交易市場根本無法存在）One can assume that the demand for used automobiles depe

23、nds most strongly upon two variables - the price of the automobile p and the average quality of used cars traded, , or Qd = D（p, ）.（假設(shè)對二手車的需求主要取決于兩個變量二手車的價格p和進入交易的二手車的平均質(zhì)量，即Qd = D（p, ）Both the supply of used cars and also the average quality will depend upon the price, or =(p) and S=S(p).（而二手車的供給和平均

24、質(zhì)量都取決于二手車的價格，即=(p) 和S=S(p)）And in equilibrium the supply must equal the demand for the given average quality, or S(p) = D (p, (p). As the price falls, normally the quality will also fall. And it is quite possible that no goods will be traded at any price level.（在均衡狀態(tài)下對于給定的平均質(zhì)量，二手車的需求等于供給，即S(p) = D (

25、p, (p)。隨著二手車交易價格下降，進入交易的二手車的平均質(zhì)量當(dāng)然也隨之降低，最終導(dǎo)致在任何價格水平下都不存在二手車交易）Such an example can be derived from utility theory. Assume that there are just two groups of traders: groups one and two. Give group one a utility function：（效用理論可以用開幫助我們解釋二手車市場的例子。假定市場上有兩類交易者，交易者1和交易者2，交易者1的效用函數(shù)為）U1=M+i=1nxiWhere M is the

26、 consumption of goods other than automobiles, xi is the quality of the ith automobile, and n is the number of automobiles.（其中，M代表交易者1對二手車之外其他商品的消費，xi表示第i輛汽車的質(zhì)量，n為汽車的數(shù)量）Similarly, let（同理，交易者2的效用函數(shù)是）U2=M+i=1n32xiThree comments should be made about these utility functions:（對于這些效用函數(shù)有三點需要說明）(1) without l

27、inear utility (say with logarithmic utility) one gets needlessly mired in algebraic complication（第一，這里采用線性效用函數(shù)（如對數(shù)效用函數(shù)）來討論問題，這樣我們就無需處理復(fù)雜的代數(shù)運算）(2) The use of linear utility allows a focus on the effects of asymmetry of information; with a concave utility function we would have to deal jointly with th

28、e usual risk-variance effects of uncertainty and the special effects we wish to discuss here.（第二，現(xiàn)行效用函數(shù)還能讓我們專注于對非對稱信息的效果。如果在凹形效用函數(shù)下進行研究，我們將不得不在考察我們最希望關(guān)注的事實的同時，考慮不確定性所帶來的風(fēng)險變動的影響）(3) U1 and U2 have the odd characteristic that the addition of a second car, or indeed a kth car, adds the same amount of u

29、tility as the first. Again realism is sacrificed to avoid a diversion from the proper focus.（第三，U1和U2具有邊際效用不變的特征，即增加第二輛車的消費所帶來的效用的增加都與增加第一輛車消費所帶來的效用增加相等。在此，我們再一次為了研究的需要犧牲了邊際效用變動的現(xiàn)實）To continue, it is assumed (1) that both type one traders and type two traders are Von Neumann-Morgenstern maximizers o

30、f expected utility; （接下來假設(shè)：（1）兩類消費者都是馮.諾依曼摩根斯坦效用函數(shù)中的追求期望效用最大化者）(2) that group one has N cars with uniformly distributed quality x, 0x2, and groupt wo has no cars;（2）交易者1擁有N輛質(zhì)量為x并且服從均勻分布的汽車，其中，交易者2沒有汽車）(3) that the price of other goods M is unity.（3）把其他商品M的價格看成為一個單位）Denote the income (including that

31、derived from the sale of automobiles) of all type one traders as Y1 and the income of all type two traders as Y2.（把各種類型的交易者1的收入（包括銷售二手汽車所帶來的收入）記作Y1，將交易者2的收入記為Y2）The demand for used cars will be the sum of the demands by both groups. When one ignores indivisibilities, the demand for automobiles by ty

32、pe one traders will be（對二手車的需求即是兩類交易者對二手車需求的總和。當(dāng)我們忽略不可整除的可能時，交易者1對二手車需求的數(shù)量可以表示為）D1=Y1p p1D1=0 ppD2=0 32pAnd（供給是）S2=0Thus total demand D (p, u) is （因此，總需求D (p, u)是）Dp,u=Y2+Y1p 如果p u Dp,u=Y2p 如果up3u2 However, with price p, average quality is p/2 and therefore at no price will any trade take place at a

33、ll: in spite of the fact that at any given price between 0 and 3 there are traders of type one who are willing to sell their automobiles at a price which traders of type two are willing to pay.（盡管有這樣的事實，即在0到3之間的某個價格下有的交易者1愿意賣掉他們的車，而有的交易者2愿意在這一價格下購買。但無論如何，在價格為p，平均質(zhì)量為p/2這種質(zhì)量均勻分布的情形中，在任何價格水平下都根本不會發(fā)生二手車

34、交易）（三）對稱信息The foregoing is contrasted with the case of symmetric information. Suppose that the quality of all cars is uniformly distributed, 0x2. Then the demand curves and supply curves can be written as follows:（上面的分析將與對稱信息下的情形形成對照。假設(shè)所有汽車的質(zhì)量是均勻分布的，0x2。那么，供給曲線和需求曲線就可以寫成如下形式：）Supply（供給曲線是）S(p)=N p1S

35、(p)=0 p1And the demand curves are（需求曲線是）D(p)=(Y1+Y2)/p p1D(p)=(Y2/p) 1p3/2In equilibrium（均衡時）P=1 如果Y2N （3）P=Y2/N 如果2Y2/3NY2 （4）p=3/2 如果N2Y2/3 （5）If N Y2, in which case the income of type two traders is insufficient to buy all N automobiles, there is a gain in utility of Y2/2 units.)（如果N Y2，此時交易者2的收入

36、不足以購買到N輛汽車，那么，將有Y2/2單位的效用收益）Finally, it should be mentioned that in this example, if traders of groups one and two have the same probabilistic estimates about the quality of individual automobiles- though these estimates may vary from automobile to automobile- (3), (4), and (5) will still describe e

37、quilibrium with one slight change: p will then represent the expected price of one quality unit.（最后，對于該例子應(yīng)該提到的是，如果兩類交易者對每輛汽車的質(zhì)量具有相同的概率估計盡管這種估計因汽車的不同而不同（3）、（4）和（5）仍將能描述均衡，只不過此時p將代表每單位質(zhì)量的期望價格）三、例證和應(yīng)用（一）保險It is a well-known fact that people over 65 have great difficulty in buying medical insurance. The

38、 natural question arises: why doesnt the price rise to match the risk? （總所周知，年齡超過65歲的人很難買到醫(yī)療保險。這就產(chǎn)生了一個問題：為什么保險費不能一直上升到風(fēng)險相當(dāng)?shù)乃?？）Our answer is that as the price level rises the people who insure themselves will be those who are increasingly certain that they will need the insurance; for error in medic

39、al check-ups, doctors sympathy with older patients, and so on make it much easier for the applicant to assess the risks involved than the insurance company.（我們的回答是，當(dāng)保險費提高時，只有那些越來越確信自己有必要投保的人才會買保險。醫(yī)療體檢中的弊端、醫(yī)生對病人的同情等因素，使得保險申請人比保險公司更加了解自己的風(fēng)險狀況）The result is that the average medical condition of insuran

40、ce applicants deteriorates as the price level rises -with the result that no insurance sales may take place at any price.（結(jié)果，當(dāng)保險費上升時，投保申請人的平均健康狀況不斷惡化，導(dǎo)致最終將不會在任何保險費水平上簽訂保險合同）This is strictly analogous to our automobiles case, where the average quality of used cars supplied fell with a corresponding f

41、all in the price level. This agrees with the explanation in insurance textbooks:（這與我們汽車市場的例子十分相似，在那里，待售舊車的平均質(zhì)量隨著市場價格的下降而下降。關(guān)于這一點，保險學(xué)教科書的解釋是這樣：）Generally speaking policies are not available at ages materially greater than sixty-five. The term premiums are too high for any but the most pessimistic (wh

42、ich is to say the least healthy) insureds to find attractive. Thus there is a severe problem of adverse selection at these ages.（通常，65歲以上人的保單是無效的。此時，保險費太高以至于除了那些最悲觀的（即健康狀況最差的）投保人而沒有其他人會對投保感興趣，因而在這一年齡存在著嚴重的逆向選擇問題）The statistics do not contradict this conclusion. While demands for health insurance ris

43、e with age, a 1956 national sample survey of 2,809 families with 8,898 persons shows that hospital insurance coverage drops from 63 per cent of those aged 45 to 54, to 31 per cent for those over 65.（以上結(jié)論與統(tǒng)計數(shù)據(jù)是一致的。1956年對2809個家庭8898個人進行的全國性調(diào)查問卷顯示，當(dāng)人們隨著年齡的增長越來越需要保險時，醫(yī)療保險的覆蓋率從4565歲人群的63%下降到65歲以上人群的31%）A

44、nd surprisingly, this survey also finds average medical expenses for males aged 55 to 64 of $88, while males over 65 pay an average of $77.（令人吃驚的是，調(diào)查顯示，5564歲之間男性的平均醫(yī)療支出是88美元，超過65歲男性的該項支出是77美元）While noninsured expenditure rises from $66 to $80 in these age groups, insured expenditure declines from $1

45、05 to $70.（然而，在該年齡段的人的非保險支出從66美元上升到80美元，保險支出則從105美元下降到70美元）The conclusion is tempting that insurance companies are particularly wary of giving medical insurance to older people.（結(jié)論是饒有趣味的：保險公司對向老人提供保險尤為謹慎）The principle of adverse selection is potentially present in all lines of insurance. The followi

46、ng statement appears in an insurance textbook written at the Wharton School:（逆向選擇問題是所有類型的保險都存在的普遍問題。下面的觀點摘自沃頓商學(xué)院的一本教科書：）There is potential adverse selection in the fact that healthy term insurance policy holders may decide to terminate their coverage when they become older and premiums mount.（當(dāng)逐漸變老的

47、那些健康保險的投保人面對保費上升時，他們就有可能決定退出保險，這種情況中便存在潛在的逆向選擇）This action could leave an insurer with an undue proportion of below average risks and claims might be higher than anticipated.（這一行動能使保險公司的客戶中高風(fēng)險客戶所占比例過高，而使保險公司可能支付比預(yù)期要高的賠償金額）Adverse selection appears (or at least is possible) whenever the individual or

48、 group insured has freedom to buy or not to buy, to choose the amount or plan of insurance, and to persist or to discontinue as a policy holder.（當(dāng)保險個人或團體能自由選擇購買或不買保險，能都自由選擇保險金和保險計劃，自由選擇維持保險或中斷保險時，逆向選擇便會出現(xiàn)，或至少可能存在逆向選擇）Group insurance, which is the most common form of medical insurance in the United S

49、tates, picks out the healthy, for generally adequate health is a precondition for employment. （團體保險是美國醫(yī)療保險中最普遍的保險形式，它用于鑒別人們的健康狀況，因為通常情況下，健康是被雇傭的一個先決條件）At the same time this means that medical insurance is least available to those who need it most, for the insurance companies do their own adverse sel

50、ection.（同時，這意味著保險公司自身的逆向選擇行動可能使那些最需要保險的人輕易得到保險）This adds one major argument in favor of medicare.（醫(yī)療保險市場上的逆向選擇現(xiàn)象為支持政府醫(yī)療保障方案提供了一個主要論據(jù)）On a cost benefit basis medicare may pay off: for it is quite possible that every individual in the market would be willing to pay the expected cost of his medicare an

51、d buy insurance, yet no insurance company can afford to sell him a policy - for at any price it will attract too many lemons.（通過成本收益分析，我們可以看到醫(yī)療保障是值得的，因為很有可能市場上所有人都希望付出一定的醫(yī)療保險的期望成本來購買保險，但卻沒有保險公司愿意出售保單，因為無論在那個價格水平下，保險合同的購買中都會有太多“檸檬”）The welfare economics of medicare, in this view, is exactly analogous

52、 to the usual classroom argument for public expenditure on roads.（從這一方面來看，對醫(yī)療保障方案的經(jīng)濟分析與平常我們關(guān)于政府利用公共支出建設(shè)馬路的討論十分相似）（二）少數(shù)名族就業(yè)The Lemons Principle also casts light on the employment of minorities. Employers may refuse to hire members of minority groups for certain types of jobs.（檸檬原則還能用來解釋少數(shù)民族就業(yè)問題。雇主可能在

53、某些職位上不愿意雇傭少數(shù)名族的職員）This decision may not reflect irrationality or prejudice -but profit maximization. For race may serve as a good statistic for the applicants social background, quality of schooling, and general job capabilities.（這種決策并非是帶有成見或者歧視，而是追求利潤最大化的結(jié)果。對于求職者的社會背景和工作能力，種族可以是一個很好的統(tǒng)計指標(biāo)）Good quali

54、ty schooling could serve as a substitute for this statistic; by grading students the schooling system can give a better indicator of quality than other more superficial characteristics.（高質(zhì)量的教育水平可以用來作為該統(tǒng)計指標(biāo)的一個補充，教育系統(tǒng)通過區(qū)分學(xué)生來作為一個比其他表面特征更優(yōu)越的顯示信號）As T. W. Schultz writes, The educational establishment dis

55、covers and cultivates potential talent. The capabilities of children and mature students can never be known until found and cultivated. (Italics added.)（正如舒爾茨所寫的那樣“興辦教育能夠發(fā)覺和培養(yǎng)潛在的天才，兒童和成人的才能如果不經(jīng)發(fā)掘和培養(yǎng)將不會被知曉”）An untrained worker may have valuable natural talents, but these talents must be certified by

56、the educational establishment before a company can afford to use them. The certifying establishment, however, must be credible; the unreliability of slum schools decreases the economic possibilities of their students.（雖然一名未受過教育的工人可能具有十分有價值的才能，但是在公司決定雇傭他之前，這些才能必須經(jīng)過教育系統(tǒng)的證明。無論如何，這種起到證明作用的系統(tǒng)應(yīng)該是可信的，貧民區(qū)學(xué)校的低的證明能力相應(yīng)地低估了學(xué)生的經(jīng)濟潛力）This lack may be particularly disadvantageous to members of already disadvantaged minority groups.