柠檬市场：质量的不确定性和市场机制(中英对照)
“柠檬”的市场质量的不确定性和市场机制【外文翻译】
外文翻译原文The market for "lemons": quality uncertainty and the marketmechanismMaterial Source: The Quarterly Journal of Economics, 1970Author:GEORGE A. AKERLOFI. INTRODUCTIONThis paper relates quality and uncertainty. The existence of goods of many grades poses interesting and important problems for the theory of markets. On the one hand, the interaction of quality differences and uncertainty may explain important institutions of the labor market. On the other hand, this paper presents a struggling attempt to give structure to the statement: "Business in underdeveloped countries is difficult"; in particular, a structure is given for determining the economic costs of dishonesty. Additional applications of the theory include comments on the structure of money markets, on the notion of "insurability," on the liquidity of durables, and on brand-name goods.There are many markets in which buyers use some market statistic to judge the quality of prospective purchases. In this case there is incentive for sellers to market poor quality merchandise, 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. It 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 welfare which can accrue to all parties. By nature, however, these institutions are non atomistic, and therefore concentrations of power with ill consequences of their own can develop.The automobile market is used as a finger exercise to illustrate and developthese thoughts. It should be emphasized that this market is chosen for its concreteness and ease in understanding rather than for its importance or realism.II. THE MODEL WITH AUTOMOBILES AS AN EXAMPLEA.The Automobiles MarketThe 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 lunch table justification for this phenomenon the pure joy of owning a "new" car. We offer a different explanation. Suppose (for the sake of clarity rather than reality) that there are just four kinds of cars. There 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.The individuals 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 lemons.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 is a lemon. This estimate is more accurate than the original estimate. 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 cars 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. It is apparent that a used car cannot have the same valuation as a new car .if it did 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 probability q of being good and a lower probability of being bad. Thus the owner 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.Gresham's law has made a modified reappearance. For most cars traded will bethe "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). But the analogy with Gresham's law is not quite complete: bad cars drive out the good because they sell at the same price as good cars; similarly, bad money drives out good because the exchange rate is even. But the bad cars sell at the same price as good cars since it is impossible for a buyer to tell the difference between a good and a bad car; only the seller knows. In Gresham's law, however, presumably both buyer and seller can tell the difference between good and bad money. So the analogy is instructive, but not complete .B. Asymmetrical InformationIt 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. For it is quite possible 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. One can assume that the demand for used automobiles depends most strongly upon two variables the price of the automobile p and the average quality of used cars traded, a, or Q = D (p, A). Both the supply of used cars and also the average quality p will depend upon the price, or p=j (p) and S=S(p). And in equilibrium the supply must equal the demand for the given average quality, or S(p) = D (p, 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.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 functionnU1= M+ ∑X ii=1where M is the consumption of goods other than automobiles, X1 is the quality of the I.T.H automobile, and N is the number of automobiles. Similarly, letnU2= M+ ∑X3/2X ii=1where M, X1, and N are defined as before. Three comments should be made about these utility functions: (1) without linear utility (say with logarithmic utility) one gets needlessly mired in algebraic complication. (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 the usual risk variance effects of uncertainty and the special effects we wish to discuss here. (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 utility as the first. Again realism is sacrificed to avoid a diversion from the proper focus.To continue, it is assumed (1) that both type one traders and type two traders are V on Neumann Morgenstern maximizers of expected utility; (2) that group one has N cars with uniformly distributed quality x, 0<x <2, and group two has no cars; (3) that the price of "other goods" M is unity.Denote the income (including that derived from the sale of automobiles) of all type one traders as Y1 and the income of all type two traders as Y2. The demand for used cars will be the sum of the demands by both groups. When one ignores indivisibility, the demand for automobiles by type one traders will be D1=Y1/p μ/p>lD1=O μ/ p<l.And the supply of cars offered by type one traders isS2= PN/2 p≤2with average qualityi= p/2.(To derive (1) and (2), the uniform distribution of automobile quality is used.) Similarly the demand of type two traders isD2 = Y2/P 3μ/2 > pD2 =0 3μ/2 < pandS2 =0.Thus total demand D (p, μ) isD (p, μ) = (Y2+ Y1)/P if p <μD (p, μ) = Y2/p if μ< p <3μ/2D(p, μ）=0 if p>3μ/2.However, with price p, average quality is p/2 and therefore at no price will anytrade take place at all: 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.C. Symmetric Information The foregoing is contrasted with the case of symmetric information. Suppose that the quality of all cars is uniformly distributed, O<x<2. Then the demand curves and supply curves can be written as follows SupplyS(p) =N p>1S(p)=O p<1.And the demand curves areD(p) = (Y2+M ay)/P p<1D(p) = (Y2/p) l<p<3/2D(p) = 0 p > 3/2.In equilibriump=1 if Y2<NP=Y2/N if 2Y2/3<N<Y2p =3/2 if N<2Y2/3.If N <Y2 there is a gain in utility over the case of asymmetrical information of N/2. (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.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 equilibrium with one slight change: p will then represent the expected price of one quality unit.III. EXAMPLES AND APPLICATIONSA.InsuranceIt is a well-known fact that people over 65 have great difficulty in buying medical insurance. The natural question arises: why doesn't the price rise to match the risk?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 medical 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. The result is that the average medical condition of insurance applicants deteriorates as theprice level rises with the result that no insurance sales may take place at any price.' This is strictly analogous to our automobiles case, where the average quality of used cars supplied fell with a corresponding fall in the price level. This agrees with the explanation in insurance textbooks: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 (which is to say the least healthy) insureds to find attractive. Thus there is a severe problem of adverse selection at these ages.The statistics do not contradict this conclusion. While demands for health insurance rise 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. And surprisingly, this survey also finds average medical expenses for males aged 55 to 64 of $88, while males over 65 pay an average of $77.3 While non insured expenditure rises from $66 to $80 in these age groups, insured expenditure declines from $105 to $70. The conclusion is tempting that insurance companies are particularly wary of giving medical insurance to older people.The principle of "adverse selection" is potentially present in all lines of insurance. The following statement appears in an insurance textbook written at the What's School: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. This action could leave an insurer with an undue proportion of below average risks and claims might be higher than anticipated. Adverse selection "appears (or at least is possible) whenever the individual or 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."Group insurance, which is the most common form of medical insurance in the United States, picks out the healthy, for generally adequate health is a precondition for employment. 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 selection."This adds one major argument in favor of medicare. 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 and buy insurance, yet no insurance company can afford to sell him a policy for at any price it will attract toomany "lemons." The welfare economics of medicare, in this view, is exactly analogous to the usual classroom argument for public expenditure on roads.B. The Employment of MinoritiesThe Lemons Principle also casts light on the employment of minorities. Employers may refuse to hire members of minority groups for certain types of jobs. This decision may not reflect irrationality or prejudice but profit maximization. For race may serve as a good statistic for the applicant's social background, quality of schooling, and general job capabilities.Good quality 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. As T. W. Schultz writes, "The educational establishment discovers and cultivates potential talent. The capabilities of children and mature students can never be known until found and cultivated." An untrained worker may have valuable natural talents, but these talents must be certified by "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.This lack may be particularly disadvantageous to members of already disadvantaged minority groups. For an employer may make a rational decision not to hire any members of these groups in responsible positions because it is difficult to distinguish those with good job qualifications from those with bad qualifications. This type of decision is clearly what George Stigler had in mind when he wrote, "in a regime of ignorance Enrico Fermi would have been a gardener, V on Neumann a checkout clerk at a drugstore."As a result, however, the rewards for work in slum schools tend to accrue to the group as a whole in raising its average quality rather than to the individual. Only insofar as information in addition to race is used is there any incentive for training.An additional worry is that the Office of Economic Opportunity is going to use cost-benefit analysis to evaluate its programs. For many benefits may be external. The benefit from training minority groups may arise as much from raising the average quality of the group as from raising the quality of the individual trainee; and, likewise, the returns may be distributed over the whole group rather than to the individual.C. The Costs of DishonestyThe Lemons model can be used to make some comments on the costs of dishonesty. Consider a market in which goods are sold honestly or dishonestly;quality may be represented, or it may be misrepresented. The purchaser's problem, of course, is to identify quality. The presence of people in the market who are willing to offer inferior goods tends to drive the market out of existence as in the case of our automobile "lemons." It is this possibility that represents the major costs of dishonesty for dishonest dealings tend to drive honest dealings out of the market. There may be potential buyers of good quality products and there may be potential sellers of such products in the appropriate price range; however, the presence of people who wish to pawn bad wares as good wares tends to drive out the legitimate business. The cost of dishonesty, therefore, lies not only in the amount by which the purchaser is cheated; the cost also must include the loss incurred from driving legitimate business out of existence.Dishonesty in business is a serious problem in underdeveloped countries. Our model gives a possible structure to this statement and delineates the nature of the "external" economies involved. In particular, in the model economy described, dishonesty, or the misrepresentation of the quality of automobiles, costs 1/2 unit of utility per automobile; furthermore, it reduces the size of the used car market from N to 0. We can, consequently, directly evaluate the costs of dishonesty at least in theory.There is considerable evidence that quality variation is greater in underdeveloped than in developed areas. For instance, the need for quality control of exports and State Trading Corporations can be taken as one indicator. In India, for example, under the Export Quality Control and Inspection Act of 1963, "about 85 per cent of Indian exports are covered under one or the other type of quality control." Indian housewives must carefully glean the rice of the local bazaar to sort out stones of the same color and shape which have been intentionally added to the rice. Any comparison of the heterogeneity of quality in the street market and the canned qualities of the American supermarket suggests that quality variation is a greater problem in the East than in the West.In one traditional pattern of development the merchants of the preindustrial generation turn into the first entrepreneurs of the next. The best documented case is Japan,but this also may have been the pattern for Britain and America.In our picture the important skill of the merchant is identifying the quality of merchandise; those who can identify used cars in our example and can guarantee the quality may profit by as much as the difference between type two traders' buying price and type one traders' selling price. These people are the merchants. In production these skills are equally necessary both to be able to identify the quality of inputs and to certify the quality ofoutputs. And this is one (added) reason why the merchants may logically become the first entrepreneurs.The problem, of course, is that entrepreneurship may be a scarce resource; no development text leaves entrepreneurship unemphasized. Some treat it as central.Given, then, that entrepreneurship is scarce, there are two ways in which product variations impede development. First, the pay-off to trade is great for would be entrepreneurs, and hence they are diverted from production; second, the amount of entrepreneurial time per unit output is greater, the greater are the quality variations.MARKET FOR "LEMONS": AND MARKET MECHANISM 497 D. Credit Marketing Underdeveloped Countries（1）Credit markets in underdeveloped countries often strongly reflect the operation of the Lemons Principle. In India a major fraction of industrial enterprise is controlled by managing agencies (according to a recent survey, these "managing agencies" controlled 65.7 per cent of the net worth of public limited companies and 66 per cent of total assets).3 Here is a historian's account of the function and genesis of the "managing agency system":The management of the South Asian commercial scene remained the function of merchant houses, and a type of organization peculiar to South Asia known as the Managing Agency. When a new venture was promoted (such as a manufacturing plant, a plantation, or a trading venture), the promoters would approach an established managing agency. The promoters might be Indian or British, and they might have technical or financial resources or merely a concession. In any case they would turn to the agency because of its reputation, which would encourage confidence in the venture and stimulate investment.In turn, a second major feature of the Indian industrial scene has been the dominance of these managing agencies by caste (or, more accurately, communal) groups. Thus firms can usually be classified according to communal origin.5 In this environment, in which outside investors are likely to be bilked of their holdings, either (1) firms establish a reputation for "honest" dealing, which confers upon them a monopoly rent insofar as their services are limited in supply, or (2) the sources of finance are limited to local communal groups which can use communal and possibly familial ties to encourage honest dealing within the community. It is, in Indian economic history, extraordinarily difficult to discern whether the savings of rich landlords failed to be invested in the industrial sector (1) because of a fear to invest in ventures con-trolled by other communities, (2) because of inflated propensities toconsume, or (3) because of low rates of return. At the very least, however, it is clear that the British-owned managing agencies tended to have an equity holding whose communal origin was more hetero-gorgeous than the Indian-controlled agency houses, and would usually include both Indian and British investors.（2）A second example of the workings of the Lemons Principle concerns the extortionate rates which the local moneylender charges his clients. In India these high rates of interest have been the lead-mon factor in landless; the so-called "Cooperative Movement" was meant to counteract this growing landless by setting up banks to compete with the local moneylenders.While the large banks in the central cities have prime interest rates of 6, 8, and 10 per cent, the local moneylender charges 15, 25, and even 50 per cent. The answer to this seeming paradox is that credit is granted only where the granter has (1) easy means of enforcing his contract or (2) personal knowledge of the character of the borrower. The middleman who tries to arbitrage between the rates of the moneylender and the central bank is apt to attract all the "lemons" and thereby make a loss.This interpretation can be seen in Sir Malcolm Darling's interpretation of the village moneylender's power:It is only fair to remember that in the Indian village the moneylender is often the one thrifty person amongst a generally thriftless people; and that his methods of business, though demoralizing under modern conditions, suit the happy-go-lucky ways of the peasant. He is always accessible, even at night; dispenses with troublesome formalities, asks no inconvenient questions, advances promptly, and if interest is paid, does not press for repay-meet of principal. He keeps in close personal touch with his clients, and in many villages shares their occasions of weal or woe. With his intimate knowledge of those around him he is able, without serious risk, to finance those who would otherwise get no loan at all.Or look at Barbara Ward's account:A small shopkeeper in a Hong Kong fishing village told me: "I give credit to anyone who anchors regularly in our bay; but if it is someone I don't know well, then I think twice about it unless I can find out all about him.Or, a profitable sideline of cotton ginning in Iran is the loaning of money for the next season, since the ginning companies often have a line of credit from Teheran banks at the market rate of interest. But in the first years of operation large losses are expected from unpaid debts due to poor knowledge of the local scene.IV. COUNTERACTING INSTITUTIONSNumerous institutions arise to counteract the effects of quality uncertainty.One obvious institution is guarantees. Most consumer durables carry guarantees to ensure the buyer of some normal expected quality. One natural result of our model is that the risk is borne by the seller rather than by the buyer.A second example of an institution which counteracts the effects of quality uncertainty is the brand-name good. Brand names not only indicate quality but also give the consumer a means of retaliation if the quality does not meet expectations. For the con-sumer will then curtail future purchases. Often too, new products are associated with old brand names. This ensures the prospective consumer of the quality of the product.consumer of the quality of the product. Chains such as hotel chains or restaurant chains are similar to brand names. One observation consistent with our approach is the chain restaurant. These restaurants, at least in the United States, most often appear on interurban highways. The customers are seldom local. The reason is that these well-known chains offer a better hamburger than the average local restaurant; at the same time, the local customer, who knows his area，can usually choose a place he prefers.place he prefers. Licensing practices also reduce quality uncertainty. For in-stance, there is the licensing of doctors, lawyers, and barbers. Most skilled labor carries some certification indicating the attainment of certain levels of proficiency. The high school diploma, the Dacca-laureate degree, the Ph.D., even the Nobel Prize, to some degree, serve this function of certification. And education to some degree, serve this function of certification. And education and labor mar-bets themselves have their own "brand names."V. CONCLUSIONWe have been discussing economic models in which "trust" is important. Informal unwritten guaranteed re preconditioning r trade and production. Where these guarantees are indefinite, business will suffer -as indicated by our generalized Gresham's law. This aspect of uncertainty has been explored by game theorists, as in the Prisoner's Dilemma, but usually it has not been incorporated in the more traditional Arrow-Dealer approach to june-dainty.2 But the difficulty of distinguishing good quality from bad is inherent in the business world; this may indeed explain many economic institutions and may in fact be one of the more important aspects of uncertainty.译文“柠檬”的市场:质量的不确定性和市场机制资料来源:《经济学季刊》,1970 作者：乔治•a•阿克尔洛夫 I介绍本文认为质量和不确定性有着某种联系，许多不同东西的存在提出了关于市场理论的有趣和重要的问题来讨论。
读《柠檬市场：质量的不确定性和市场机制》兼议如何解决市场信息不对称问题
读《柠檬市场：质量的不确定性和市场机制》兼议如何解决市场信息不对称问题一、《柠檬市场：质量的不确定性和市场机制》概述和观后感柠檬市场，也称次品市场，也叫做阿克洛夫模型。
它是是指在信息不对称的市场中，产品的卖方对产品的质量拥有比买方更多的信息。
而在极端情况下，市场会止步萎缩和不存在，这其实就是信息经济学中的逆向选择问题。
柠檬市场效应则是指在信息不对称的情况下，质量好的商品遭受淘汰，而质量差的商品会逐渐占领市场，从而取代质量好的商品，从而导致市场之中充斥着劣质商品。
这和一个经济学名词“劣币驱逐良币”异曲同工，在远古的铸币时代，当那些质量和成色低于法定铸币的货币——“劣币”进入流通领域之后，人们就倾向于将那些价值高的货币——“良币”收藏起来。
最后，良币将被劣币驱逐，市场上就只流通下劣币了。
交易当事人的信息不对称是“劣币驱逐良币”现象存在的基础。
因为如果交易双方对货币的成色或者真伪都已经十分地了解，劣币持有者就很难将手中的劣币用出去，或者，即使能够用出去也只能按照劣币的“实际”而非“法定”价值与对方进行交易。
一般说来，货币是作为一般等价物的特殊商品，当货币的接受方对货币的成色或真伪缺乏信息的时候，就会想办法提供价值更低的交易物，而交易物的需求方也就是支付货币的一方相应地也会想办法用更不足值的货币来进行支付，最终导致整个市场充斥劣币。
在产品市场上，显然卖家比买家拥有更多的信息，因此两者之间的信息是非对称的。
买者肯定不会相信卖者的话，但即使卖家说的天花乱坠。
买者唯一拥有的办法只有压低价格以避免信息不对称带来的风险损失。
因此这样买者出过低的价格也使得卖者不愿意提供高质量的产品，从而使得低质量产品充斥市场，高品质产品被逐出市场，最后整个产业产品市场萎缩退步。
为了更清楚地说明这个现象，我们假设市场中好车与坏车并存，每100 辆二手车中有50 辆质量较好的、50 辆质量较差，质量较好的车在市场中的价值是50 万元，质量较差的价值10万元。
柠檬市场：质量的不确定性与市场机制
２００１年诺贝尔经济学奖得主—乔治·阿克洛夫经济学思想述评瑞典皇家科学院于10月10日宣布，将本年度诺贝尔经济学奖授予美国经济学家乔治·阿克洛夫、迈克尔·斯宾塞和约瑟夫·斯蒂格利茨，以表彰他们运用不对称信息理论研究市场经济所取得的成就。
众所周知，诺贝尔经济学奖认可的都是经过实践检验的理论成果，而经济学理论成果经过实践检验被认为是正确的，通常需要20、30年。
此次获奖三人的理论成果主要集中在20世纪70年代。
他们的获奖意味着国际上正式承认其理论具有广泛的应用价值。
瑞典皇家科学院在其新闻公报中称，许多市场都存在信息不对称现象：买卖的一方往往掌握比另一方更多的信息。
借款人比贷款人更了解自己的还贷潜力，企业经理和董事会比股民更了解企业的未来，客户比保险公司更了解他们发生事故的风险率。
而一个市场经济的有效运作，需要买者和卖者之间拥有充分的共同信息。
如果信息不对称现象非常严重，那么就有可能限制市场功能的发挥，在极端情况下，会使整个市场不存在。
此次获奖的三位经济学家分别从产品市场、劳动力市场、保险及资金市场等领域探讨了信息不对称问题，指出市场体制需要完善、设计。
这是对传统经济学的重大突破。
他们的研究揭示了当代信息经济的核心问题，奠定了关于市场经济不对称信息理论的基础，其分析理论用途广泛，既适用于对传统的农业市场的分析研究，也适用于对现代金融的分析研究。
本文主要是对乔治·阿克洛夫的一些主要经济思想进行简单的评述，以便大家更深刻地了解这位世界一流的经济学家。
一、乔治·阿克洛夫生平简介乔治·阿克洛夫(George A.Akerlof)1940年出生于美国康涅狄州纽黑文，现年61岁；1962年，在耶鲁大学获得学士学位；4年后在麻省理工学院获得博士学位。
他曾担任伦敦经济学院货币银行专业的经济学教授、经济顾问委员会高级经济学家、布鲁金斯小组(Brooking Panel)经济问题高级顾问和美国经济联合会副主席；现任加州大学伯克利分校经济学教授。
柠檬市场：质量的不确定性和市场机制(中英对照)
The Markets for “Lemons”:Quality uncertainty and The Market Mechanism柠檬市场：质量的不确定性和市场机制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.（本文论述的是质量和不确定性问题。
现实中存在大量多种档次的物品给市场理论提出了饶有趣味而十分重大的难题）On the one hand, the interaction of quality differences and uncertainty may explain important institutions of the labor market.（一方面，质量差异和不确定性的相互作用可以解释劳动力的重要机制）On the other hand, this paper presents a struggling attempt to give structure to the statement: "Business in under-developed countries is difficult"; in particular, a structure is given for determining the economic costs of dishonesty.（另一方面，本文试图通过讨论获得这样的结论：在不发达国家，商业交易是困难的，其中，特别论及了欺骗性交易的经济成本）Additional applications of the theory include comments on the structure of money markets, on the notion of "insurability," on the liquidity of durables, and on brand-name goods.（本文的理论还可以用来研究货币市场、保险可行性、耐用品的流动性和名牌商品等问题）There are many markets in which buyers use some market statistic to judge the quality of prospective purchases.（在许多市场中，买者利用市场的统计数据来判断他们将要购买的商品的质量）In this case there is incentive for sellers to market poor quality merchandise, 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.（在这种情况下，卖者有动力提供低质量商品，因为某种商品的价格主要取决于所有同类商品质量的统计数据而非该商品的实际质量。
the market for lemons解读
the market for lemons解读
柠檬市场（The Market for Lemons）是一个经济学概念，它指的是信息不对称的市场，即买卖双方对商品或服务的真实信息了解程度不同。
柠檬市场中的买家通常对商品或服务的质量不确定，因此他们可能会根据平均质量来决定价格，从而使得高质量的产品或服务因为价格过高而难以出售，而低质量的产品或服务则可能以高价出售。
这个概念来源于美国俚语中的“柠檬”，表示“次品”或“不中用的东西”。
在柠檬市场中，由于信息不对称，买家往往难以判断商品或服务的质量，因此他们可能会采取平均质量的预期来决定价格。
这种平均质量的预期价格可能会使得高质量的商品或服务难以出售，因为他们无法与低质量的商品或服务区分开来。
柠檬市场的存在对经济效率和市场秩序产生了一定的影响。
它可能导致市场上的优质商品或服务被排挤出市场，而低质量的产品或服务则可能占据主导地位。
这不仅影响了市场的公平性和竞争性，还可能导致市场的萎缩和消失。
为了解决柠檬市场的问题，需要采取一些措施来增加市场的透明度和信息对称性。
例如，政府可以加强监管和信息披露要求，提高市场的透明度；卖家也可以采取一些措施来增加商品或服务的可追溯性和质量保证，从而增强买家的信心。
此外，买家也可以通过提高自身的信息获取能力和风险意识，来降低信息不对称的影响。
柠檬法：美国的汽车“三包”法
在汽车“三包”中具有核心地位，由于目前欧洲和日本都没有专门的汽车“三包”法，所以比较具有借鉴性的就是美国的柠檬法。
正所谓它山之石可以攻玉，或许我们可以从对柠檬法概况和实施结果的分析中吸取经验，完善中国自己的汽车“三包”法案。
Market for Lemons: Quality Uncertainty and the Market Mechanism），主要讨论了信息不对称理论对二手车市场的影响，文中把质量AUTO REVIEW「98」时讯堂业界聚焦“三包”专题消费者除了要求退还车款外，还可以要求赔偿拖车、修车、租车和律师费用。
根据柠檬法退车时，退款会因为车的使用情况进行打折。
美国汽车消费者维权途径多元化由于柠檬法的保护，美国消费者退换问题车并不需要经过复杂的程序，只要达到条件，就可以通过消费者协会索赔，不必上法庭。
另外消费者还可以通过仲裁调解，如果仲裁败诉，仍可以上法庭起诉。
而且美国的法律体系主要保护消费者的利益，进入诉讼程序，一旦上报到美国商务部，商务部会对汽车产品问题进行严格调查和处罚。
美国的消费者协会起到很重要的作用，他们代表消费者的利益。
如果消协发现质量问题，会在内部杂志上通报，号召抵制该产品，对汽车制造商带来巨大的打击。
在鉴定汽车质量方面，柠檬法规定让制造商自己排除质量隐患，而不是“谁主张谁举证”，改变了消费者因为技术、财力、精力匮乏而导致的劣势状态。
但是汽车制造商不会轻易让消费者退换汽车，一方面不希望助长退换风气造成太多损失，另一方面出于对自己声誉的维护。
车企为了规避退换车，在法庭上往往想办法把责任推给消费者，证明消费者没有正确使用车辆、没有定期保养车辆、对车辆进行改装等行为导致车辆出问题。
车企还会通过向法官或者仲裁者申请额外的最后一次维修机会来避免退换，理由可能为车厂有新维修方法来处理之前未能修好的质量缺陷，而这种“维修判决”往往会让消费者感到失望。
车企收回的柠檬车在整修之后还会再次出售，但是根据柠檬法的规定，再次出售车窗上必须贴有“柠檬”标志，文件上也必须注明是“柠檬法回购车”（Lemon Law Buyback），出售的柠檬车至少要有1年的保质期，依然受到柠檬法的保护。
柠檬市场：质量的不确定性和市场机制(中英对照)
The Markets for “Lemons”:Quality uncertainty and The Market Mechanism柠檬市场:质量的不确定性与市场机制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、(本文论述的就是质量与不确定性问题。
现实中存在大量多种档次的物品给市场理论提出了饶有趣味而十分重大的难题)On the one hand, the interaction of quality differences and uncertainty may explain important institutions of the labor market、(一方面,质量差异与不确定性的相互作用可以解释劳动力的重要机制)On the other hand, this paper presents a struggling attempt to give structure to the statement: "Business in under-developed countries is difficult"; in particular, a structure is given for determining the economic costs of dishonesty、(另一方面,本文试图通过讨论获得这样的结论:在不发达国家,商业交易就是困难的,其中,特别论及了欺骗性交易的经济成本)Additional applications of the theory include comments on the structure of money markets, on the notion of "insurability," on the liquidity of durables, and on brand-name goods、(本文的理论还可以用来研究货币市场、保险可行性、耐用品的流动性与名牌商品等问题)There are many markets in which buyers use some market statistic to judge the quality of prospective purchases、(在许多市场中,买者利用市场的统计数据来判断她们将要购买的商品的质量)In this case there is incentive for sellers to market poor quality merchandise, 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、(在这种情况下,卖者有动力提供低质量商品,因为某种商品的价格主要取决于所有同类商品质量的统计数据而非该商品的实际质量。
两种市场中“柠檬”问题的比较分析
场上 销售 商的身 份也 很难识 别 。一 家 网上商 店可 以在 一 天 内建 立 起来 ， 可 以 在第 二 天 就 消失 。 由于 也 这 种不 确定 性 的存 在， 市场运 作的效 率将 十分低 下 ， 时甚至 根本 就无法 运作 。 有 还 有两个 原 因使得 “ 柠檬” 问题在 网络 市场的表 现将 更 加 突 出 ： 是 数 字 产 品不 只是 纸上 产 品 的数 一 字版 ， 它还包含 了 电子 媒介 的独特优 点 。比如 ， 网上 的报纸被 个性化 和定 制化 ｌ， 以随时更 新 ， 『 可 因此质
《柠檬” “ 市场 ： 品质不确 定性与市 场机制） Ｔ ｅｍ ｒ ｔｏ ｌ ａ ’ ｑａｔｉ ｎ ｒｉｙａｄｔ ａ ｅ （ｈ ａ ｅ ｆ ｅ ｏ ：ｕｌ ｔｅｕｃ ｔｎ ｎ ｅｍ ｒ ｔ ｋ ｒ‘ ａ ｎ ｉ ｖ ａ ｅａ ｔ ｈ ｋ
ｍ ｃａｉ ， ｅｈｎｓ 对非 对称信 息条 件下 市场运行 效率 进行 了分 析 ， 出 了“ 檬” ｍ） 得 柠 原理 （ 柠 檬” 源于 美 国 口 “ 来 语对 “ 陷车 ”“ 缺 、二手 车” 的经验 称呼 ）并 且 开创 了逆 向选 择 （ｄｅ ｅｓｌ ｔｎ理论 。阿克 洛夫 以 旧汽 车 ， ａｖｒ ｅ ｉ ） ｓ ｅ ｃｏ 市场 为例 ， “ 檬” 对 柠 问题进 行 了经典 的分析 。在 旧车 市场 上 ， 既定 的卖者 和关 心 旧车质 量 的买者 之 间存
在着信 息的非对称性 ， 卖者知道车的真实质量 ， 买者不知道 ， 在他不能确知所购车辆的内在 质量 的前提
下， 他愿 意接受 的价 格也 只能是所 有 旧车价值 按概 率加权 计算 的一 个平 均值 ， 因而 只愿 意根 据平 均值 来 支付 价格 ， 但这样 一来 ， 质量 高于 平均值 水平 的卖 者就 会退 出交易 ， 有 质量 低 的 卖者 进 入 市 场 。也 就 只 是说 只 有低 质量 的汽车 出售 ， 而投有 高质量 的 旧汽 车交 易 ， 果是 低质量 旧汽车将 高 质量 旧汽车 挤 出交 结 易市 场 。 由此 ， 阿克 洛夫 解释 了为什 么即使是 只使 用过一 次 的“ ” 新 汽车 ， 在柠 檬市 场上 也难 以卖 到 好价 钱 。这一 过程 不断持 续 ， 最后市 场上只剩 下损 失最 严重 的 旧车 ， 所有 好 一 点 的 旧车都 会 从市 场 上 消失 于是 ， 市场上 只剩 下 了劣 质商 品— — “ 檬” 柠 。 “ 檬” 柠 原理 对经 济学 的贡献 在于 ， 它揭示 了许 多市场 都存 在 的信 息 的非对 称现 象 ， 深化 了我 们对 真 实市 场现 象 的 了解 。一个 市场 经济 的有效运 行 ， 需要买 者 和卖 者 之 间有 足够 的共 同 的信 息 。如果 信 息 不对称 非 常严 重 ， 就有 可 能限制 市场功 能 的发挥 ， 引起市 场交易 的低 教率 ， 至会导 致 整个 市场 的失 灵 。 甚
中文版-柠檬市场：质量的不确定性和市场机制
“柠檬”市场：质量的不确定性和市场机制乔治·阿克洛夫关键词：信息经济学；质量不确定性；市场机制；“柠檬市场”；信息不对称一. 引言本文论述的是质量和不确定性问题。
多种档次的物品给市场理论提出了有趣而又重要的问题。
一方面，质量差异和不确定性的相互作用可以解释某些重要的劳动市场制度。
另一方面，本文力求对如下主张，即“在不发达国家做生意是因难的”给出一个模型。
尤其是要给出一个用于确定不诚实的经济成本的模型。
理论的应用还包括对货币市场结构、不可保险性、耐用品的流动性以及品牌产品的评论。
在许多市场中，购买者总是利用某些市场统计数据来判断欲购商品的质量。
在这种情况下，销售者就有动机销售劣质商品，因为从优质商品中受益的主要是其统计数据受影响的销售者整体而不是单个销售者。
结果是，产品的平均质量往往会下降，市场规模相缩小。
还应该看到的是，在这些市场中，社会收益和私人收益是有差别的，因此，在某些情况下，政府干预可以增加各方的福利。
或者是，私人制度可能会产生，以利用各方潜在的福利增长。
但是，这些制度并不是孤立分散的(Nonatomistic)。
因此，权力的集中有可能形成——这就是制度本身带来的不良后果。
本文试图用汽车市场来阐述上述思想。
应该强调的是，之所以选择汽车市场，是因为它非常具体并且易于理解，而不是因为它的重要性或现实性。
二. 以汽车为例的模型1．汽车市场旧车市场的例子说明了问题的本质。
用以解释这种现象的常见理由是，拥有一辆新车可以带来快乐，而我们却给出了另一种解释。
假定(为了说明问题，而不是现实情况)市场中只有4种汽车，即新车和旧车，好车和次品车(在美国，也称之为“柠檬”)。
新车有可能是好车，也有可能是次品车；当然，旧车也是如此。
人们在上述市场中购买一辆新车时，并不知道他所购买的汽车是好车还是次品车。
但是，假定在生产出来的汽车中，好车的比例为q, 次品车的比例为1-q. 则买主必定知道买到好车的概率为q, 买到次品车的概率为1-q.然而。
柠檬市场：质量的不确定性与市场机制
柠檬市场：质量的不确定性与市场机制２００１年诺贝尔经济学奖得主―乔治・阿克洛夫经济学思想述评瑞典皇家科学院于10月10日宣布，将本年度诺贝尔经济学奖授予美国经济学家乔治・阿克洛夫、迈克尔・斯宾塞和约瑟夫・斯蒂格利茨，以表彰他们运用不对称信息理论研究市场经济所取得的成就。
众所周知，诺贝尔经济学奖认可的都是经过实践检验的理论成果，而经济学理论成果经过实践检验被认为是正确的，通常需要20、30年。
此次获奖三人的理论成果主要集中在20世纪70年代。
他们的获奖意味着国际上正式承认其理论具有广泛的应用价值。
瑞典皇家科学院在其新闻公报中称，许多市场都存在信息不对称现象：买卖的一方往往掌握比另一方更多的信息。
借款人比贷款人更了解自己的还贷潜力，企业经理和董事会比股民更了解企业的未来，客户比保险公司更了解他们发生事故的风险率。
而一个市场经济的有效运作，需要买者和卖者之间拥有充分的共同信息。
如果信息不对称现象非常严重，那么就有可能限制市场功能的发挥，在极端情况下，会使整个市场不存在。
此次获奖的三位经济学家分别从产品市场、劳动力市场、保险及资金市场等领域探讨了信息不对称问题，指出市场体制需要完善、设计。
这是对传统经济学的重大突破。
他们的研究揭示了当代信息经济的核心问题，奠定了关于市场经济不对称信息理论的基础，其分析理论用途广泛，既适用于对传统的农业市场的分析研究，也适用于对现代金融的分析研究。
本文主要是对乔治・阿克洛夫的一些主要经济思想进行简单的评述，以便大家更深刻地了解这位世界一流的经济学家。
一、乔治・阿克洛夫生平简介乔治・阿克洛夫(George A.Akerlof)1940年出生于美国康涅狄州纽黑文，现年61岁；1962年，在耶鲁大学获得学士学位；4年后在麻省理工学院获得博士学位。
他曾担任伦敦经济学院货币银行专业的经济学教授、经济顾问委员会高级经济学家、布鲁金斯小组(Brooking Panel)经济问题高级顾问和美国经济联合会副主席；现任加州大学伯克利分校经济学教授。
explanation for lemon market
Classroom Games:A Market for LemonsCharles A.Holt and Roger Sherman*Journal of Economic Perspectives,Winter1999I.IntroductionIf product quality cannot be observed by buyers prior to purchase,then sellers will be tempted to skimp on it.Buyers then become reluctant to pay high prices as they learn to expect low-quality products--or"lemons."The"lemons market"terminology is due to George Akerlof (1970),who explained how the pressure of competition may cause quality to deteriorate to such low levels that the market may fail to exist.This lemons outcome is discussed in some introductory and most intermediate microeconomics courses,and it is examined in some detail in a range of applied courses:industrial organization,regulation,antitrust,managerial economics, law and economics,game theory,and experimental economics.The incentives that arise in markets with asymmetric information are illustrated in the classroom exercise presented here.Student sellers choose both a quality"grade"and a price for their products.Initially,both prices and grades for all sellers are posted,and buyers select from these offerings.In this full-information setup,the market prices and grades quickly reach efficient levels that maximize total surplus.Next,although sellers continue to choose grades and prices,only prices(not grades)are posted for buyers to see when they shop.The grades and prices then fall to inefficiently low levels.The observed market outcomes in this exercise can stimulate useful discussion of asymmetric information,market failure,and remedies such as quality standards and warranties.*Depatment of Economics,Rouss Hall,University of Virginia,Charlottesville,Virginia.We wish to thank Sanem Eruçar for suggestions and comments.We are also indebted to Alstair Fisher,who first told us that he used the Holt and Sherman(1990)parameters in classroom market games.II.ProceduresPrepare for the exercise before the start of class by setting up a record table on the blackboard or overhead projector.There should be a column for each seller,with the seller number written at the top,and with enough rows for about six periods.Each cell of the table will be used to record the price,grade,and units sold for each seller in each period.Table 1gives an example of such a table,fully filled out after six periods,although you would obviously begin with a blank table.This exercise begins by selecting sellers and buyers,and distributing to them copies of Table 1.Price and Grade Outcomes by Periodseller 1seller 2seller 3period 1(full information)$11.50grade 31units $6.00grade 22units $12.00grade 31unit period 2(full information)$5.75grade 22units $5.50grade 21unit $1.90grade 11unit period 3(full information)$5.65grade 21unit $5.60grade 22units $5.60grade 21unit period 4(only price information)$2.40grade 11unit $5.60grade 21unit $2.40grade 12units period 5(only price information)$2.40grade 11unit $1.65grade 11unit $5.50grade 12unitsthe instructions for each group contained in the appendix.The instructions and record sheets can conveniently fit on the same page if margins and fonts are adjusted.We have found that a market with three sellers and four buyers works well.We have also used six sellers and eight buyers.A larger number of buyers makes a period last too long,because in this exercise buyers make purchase decisions in sequence.Rather than expand the numbers for larger classes,it is better to have buyers and sellers be represented by teams composed two or three students each.An added benefit is that discussion among members of a team may promote understanding and interest.For even larger classes,it is best to have some observe while others participate.To avoid communication between buyers and sellers,the buyers,sellers,and observers(if there are any)should be seated in separate rows or areas.Begin by reading aloud the text of the instructions where it is the same for buyers and sellers.However,do not reveal the private information tables of sellers’costs and buyers’values, and there is no need to read through the record tables for keeping track of decisions and earnings. One purpose of keeping value and cost information private is to see whether the market can yield an optimal quality grade that could not be calculated on the basis of any one person’s information.It is useful at this stage to allow a few minutes for questions about the rules of the game. Sellers,for example,will often want to know if they are required to sell units of only one quality in a period(yes,and also at only one price,although the grade and price can be changed or left unchanged in later periods).Sellers may ask if they can refuse an offer to buy(yes),or whether they incur costs for units not sold(no).Of course,you should avoid any explanations to students that might tend to reveal the underlying conditions in the market.For example,if somebody asks about another’s private value or cost information,or whether buyers’or sellers’values or costs are all the same,do not answer the question.After procedural questions are settled,open the market by inviting the sellers to decide on the grade and price for the first period.Sellers earn money by selling at a price above the cost for the grade that they choose,although they are limited to selling no more than two units of the product in a period.Once all sellers have recorded their decisions on their instruction/record forms,collect the information and write grades and prices in the proper seller column on the blackboard or overhead projector.Then return forms to the sellers,and choose which buyer will begin the shopping.The easiest procedure is to draw lots:whoever received the marked lot draws first,and then move through the group in a preannounced manner,say,left to right or counterclockwise.The first buyer in the sequence gets to choose whether to purchase,and if so,from which seller.Buyers can purchase only one item per period.They earn money by buying at a price below the money value of the unit that they purchase;this value can be thought of as the value for which the buyer could resell the unit.Presumably,the seller will wish to accept and sell a first unit,but the seller may not wish to sell a second unit if the price does not cover its cost. When a transaction is agreed upon,go on to the next buyer.As buyers make purchases,use the record table on the blackboard to keep track of the number of units sold by each seller,and draw a line though the price of a seller who has sold two units.After all buyers have finished,ask sellers to make grade and price choices for period two.Again,Table1gives an example of such a table,fully filled out after six periods.Figure1.Demand and Supply Arrays by GradeThe structure of supply and demand for each period is determined by the information provided in the instruction sheets.Market demand is determined by the resale values known to buyers.Buyers have identical valuations.Each buyer can purchase at most a single unit of thecommodity in a period,and the value of that unit depends on the grade:$4for grade1,$8.80 for grade2,and$13.60for grade3.An individual buyer’s demand for a grade1product is, therefore,perfectly inelastic at all prices below$4.Thus,with four buyers and a grade of1,for example,the market demand would be vertical at a quantity of4units for any price below$4, as shown by the D1curve in the lower part of Figure1.Market supply is determined by the costs given to sellers.Each seller has a capacity of two units,with the cost of the second unit being$1higher than the cost of the first unit.For a grade of1,the costs for the first and second units produced are$1.40and$2.40respectively,so the individual seller’s supply curve would have two steps,before becoming perfectly inelastic at two units for prices above$2.40.With three identical sellers,the market supply will also have two steps with three units on each step. The market supply for grade1is labeled S1in the lower part of Figure1,and it crosses the D1 curve at a price of$2.40.The supply and demand curves for the other grades are shown above those for grade1.Notice that in Figure1,the sum of consumer and producer surplus is maximized at a grade of2.1Sometimes the market will have settled at the optimal grade(of2) by the second period,and it should do so by the fourth period.When satisfied that the market is reasonably efficient in the sense of having settled on the correct grade,announce a change.Now,sellers are to choose grade and price,just as before,but now only price will be posted on the blackboard for buyers to see when they make their purchase decisions.Buyers do not find out the grade of their purchase until the instructor write all sellers’grades in the table after all buyers are finished shopping.This change must be announced before sellers make price and grade decisions for a period,and we try to do it with a straight face,so as not to hint that there are now new possibilities for taking advantage.Except for this informational difference,the procedures are the same as before.Two periods will usually establish an equilibrium at the lowest quality level1,which of course is not the socially optimal outcome.To summarize:1)Before class,prepare separate buyer and seller instructions,with the1The calculations can be simplified by using even dollar amounts for the costs and values.It is useful to keep the $1difference between the first and second unit costs,and to ensure that surplus is maximized at an intermediate grade of two.One possibility is to use more than three grades so that the optimal grade is not exactly in the middle.Some parameterizations with larger numbers of grades are used in Holt and Sherman(1990).We prefer to use only three grades in order to obtain quicker convergence in the full information periods.appropriate information and record tables for each.2)Based on the number of students expected, decide on the numbers of buyers and sellers and on the number of students to serve on each buyer or seller team.Minor adjustments can be made when the number of students attending class is known.Photocopy enough buyer and seller instruction/record sheets for participants and observers.3)Prepare the record table on the blackboard,as in Table1.4)Distribute seller instructions to sellers and buyer instructions to buyers,keeping the two groups separate.Read the common text aloud,skipping over the private cost and value information,and answer procedural questions.5)Begin the full information periods by asking sellers to make their grade and price decisions for period1.6)Collect seller decision sheets,post grades and prices for each seller,and return decision sheets to sellers.7)Draw lots to determine the order of buyer shopping decisions,and make sure the seller agrees to each purchase request.8)When an equilibrium grade develops,announce that in future periods only price(not grade)will be posted on the board,and continue with this revised procedure for several more periods.The exercise will take about an hour--ten minutes for instructions and about seven minutes for each period--plus time for discussion.III.DiscussionWe begin by illustrating outcomes for an undergraduate"Economics of Regulation"class at the University of Virginia.The21students were assigned to teams corresponding to the three sellers and four buyers;thus,each team had from two to four students,and one student served as a recorder.(We have obtained similar results in a number of larger undergraduate classes with more buyers and sellers,but the data from a small class are easier to display.)Table1,already presented,shows the pattern of results from this class.It took three periods before the full information market settled on the optimal grade of two.Notice that the prices in this period have converged to the sellers’cost of a second unit of grade two,which is$5.60.This convergence to the optimal grade is expected,but the convergence the competitive price for that grade is not observed in all classes.In the final two periods when the grade information from sellers was not available to buyers,the grades fell to a suboptimal level.There is a clear rip-off in period five, where two low-quality units were purchased at a price of$5.50that is about at the previous going price for units of grade two.Class discussion typically begins with the most salient result,the dramatic decline of price and grade in the asymmetric-information periods.Students are usually able to see that when buyers have less information,the sellers can take advantage of the situation and cut quality,and then buyers react to protect themselves.Follow up with questions investigating whether buyers or sellers benefit from the lower grade/price combinations:"Why is a low grade bad anyway, isn’t it better for buyers to get the low prices that resulted?"The answer--that the value to the buyers fell by more than price--leads to the next question:"Sellers cut costs when they lowered the grade;will sellers be better off when the grade falls?"The answer depends on how low price falls,and some sellers may benefit from selling low grade units at a deceptively high price.If you have trouble eliciting discussion with these types of questions,try something more confrontational,like asking for a"sellers’representative"to offer an explanation of why prices had to fall,and for a response from a"buyers’representative."Some sellers might claim that they did not want to cut grade,but that buyers got burned by other sellers and seemed to prefer a low price at which it is only profitable to offer a low grade.Bans against price advertising, such as those employed by professional associations,were typically defended by the claim that price advertising would create pressure to lower quality to achieve lower costs.However,the Federal Trade Commission began to oppose such bans a little over ten years ago.After everyone agrees that the low-grade outcome is bad for all concerned,consider the question of how much buyers and sellers as a group would benefit from a higher grade.To address this issue,students should be given complete value and cost information for both sides of the market,so that they can focus on the difference between buyer values and seller costs for the number of units sold.Instead of asking why grade2is optimal,it is better to ask whether a regulator would want to insist on the highest grade.The answer is no;in moving from grade2 to3,buyers’values go up by$13.60-$8.80=$4.80,whereas sellers’costs go up by$12.00-$5.60=$6.40.Be sure and make the point that grade can be too high as well as too low.By this time,students can see that grade2is optimal,in the sense that it creates greater gains for sellers and buyers together.They might also notice that if valuations were different across buyers,then more than one grade might survive in equilibrium.For example,some sellers might cater to buyers who place a higher valuation on high quality,and other sellers may serve the more price-sensitive buyers.Students seldom can see how the second-unit cost for theoptimal grade will determine the full-information equilibrium price,but this can be established by questions that lead them to construct supply and demand curves in Figure1;the type of questions that lead to the discovery of supply and demand curves are outlined in an earlier installment of this column concerning a"pit market"(Holt,1996).Note that the prices in the full-information setup may not fall to the competitive level for the optimal grade,which could be due to the fact that sellers are price setters in a market without active counteroffers from buyers.Next,the discussion should turn to factors that may remedy the inefficiencies caused by asymmetric information.It is pleasing when students figure out how warranties can overcome this problem,by protecting buyers and thus making their defensive behavior unnecessary.In markets with repeat purchases,sellers can establish and maintain reputations for the quality they provide,and an efficient outcome may evolve even when buyers cannot observe quality before the purchase.It is also useful to push the discussion toward the problems faced by a potential regulator. Such a regulator is not likely to know value and cost information with precision;the values and costs can change;the regulator may be lobbied by seller and consumer groups that have unequal power;the lobbying itself uses up real resources;and so on.These observations suggest the merits of more flexible and less intrusive forms of regulation,like forcing disclosure of quality where that is possible,ensuring that seller warranties are clearly written and consistently honored, and allowing professional associations to set quality standards.In an antitrust class,you might want to ask under what conditions a quality standard might be anticompetitive;for example,the quality standard might be so high as to exclude new entry,or so rigid as to deter innovation.IV.Further ReadingA number of experimental studies of markets with asymmetric quality information have been carried out.Lynch et al.(1986)document lemons outcomes in laboratory double auctions, and they investigate the effects of warranties,requirements for truthful advertising,and so on. Holt and Sherman(1990)also used laboratory experiments to evaluate factors that affect the degree to which quality deteriorates when it is not observed by buyers;the present classroom exercise is adapted from their setup.DeJong,Forsythe,and Lundholm(1985)allowed sellers tomake price and quality representations,but the quality representation did not have to be accurate, and the buyer had imperfect information about quality even after using the product.Finally, Miller and Plott(1985)report experiments in which sellers can make costly decisions that "signal"high quality,which might prevent quality deterioration.This literature is surveyed in Davis and Holt(1993,ch.7)and Holt(1995).10Appendix:Instructions for Buyers and SellersSeller Instructions for Seller Number______This is a market with buyers and sellers.The sellers will begin by choosing a price and a quality"grade."We will collect these decisions and write them on the blackboard. Then we will give buyers the chance to purchase from one of the sellers at the grade and price listed.The grade can be any number from1to3;a higher grade costs more to produce and is worth more to buyers.The table below shows your costs of different grades if you are a seller,and it shows your money values of different grades if you are a buyer.grade1grade2grade3seller cost of1st unit$1.40$4.60$11.00seller cost of2nd unit$2.40$5.60$12.00Each buyer can buy only1"unit"of the commodity during a period.Each seller can sell up to2units in a period,but the2nd unit costs$1more to produce.If you are a seller,the top row of the table above shows the cost of the1st unit that you actually sell in a period(for the grade you choose),the2nd unit costs$1more than the1st unit.Unsold units are not produced and hence incur no cost.Buyers earn money by making a purchase at a price that is below the value,which depends on the quality grade.The value to the buyer depends only on the grade,not on whether it is the seller’s1st or2nd unit in the period.A buyer’s earnings are calculated as the difference between the value and the purchase price:buyer earnings=value for grade purchased-seller’s price.If a buyer does not make a purchase,the buyer earns$0.Sellers earn money by making one or more sales at a price that is above the cost of the unit(determined from the table above).A seller’s earnings are calculated as the sum of the earnings on the units actually sold:seller earnings=sale price-cost of grade produced.A seller who does not make a sale in a period will earn$0.When all sellers have finished choosing their prices and grades for the period,we will collect these sheets and write the prices and grades on the blackboard under the seller numbers.Then I will draw lots to determine a buyer number,and that buyer can purchase a unit from one of the sellers or from no seller.Buyers are then chosen in order;if buyer2 goes first,then buyer3is second,...and buyer1is last.Once a seller has sold a unit,the2nd unit costs$1more,so the seller will be asked whether or not the seller wishes to sell a 2nd unit at the advertised price and grade.If a2nd unit is sold,it must be at the same price and grade as the1st unit.If a seller refuses to sell or sells both units in a period,I will draw a line through that seller’s price.You can use the table below to calculate(hypothetical)earnings.Any questions?We will begin by having each seller choose a price and grade for period1,which you should write in the top two rows of your record table.pd.1pd.2pd.3pd.4pd.51)grade for current period_________________________2)price for current period_________________________3)sales price on1st unit_________________________4)cost of1st unit_________________________5)profit on1st unit:(3)-(4)_________________________6)sales price on2nd unit_________________________7)cost of2nd unit_________________________8)profit on2nd unit:(3)-(4)_________________________9)total profit:(5)+(8)_________________________10)cumulative profit_________________________Buyer Instructions for Buyer Number______(Use the same initial paragraph as for sellers.)grade1grade2grade3buyer value$4.00$8.80$13.60 (Remaining instructions are the same as for sellers.)pd.1pd.2pd.3pd.4pd.51)ID of seller of product_________________________2)grade of product_________________________3)value to you(from table)_________________________4)purchase price_________________________5)earnings:(3)-(4)_________________________6)cumulative earnings_________________________ReferencesAkerlof,George A.,"The Market for’Lemons:’Quality Uncertainty and the Market Mechanism,"Quarterly Journal of Economics,August1970,84,488-500.Davis,Douglas D.,and Charles A.Holt,Experimental Economics,Princeton:Princeton University Press,1993.DeJong,D.V.,Robert Forsythe,and Russell Lundholm,"Ripoffs,Lemons,and Reputation Formation in Agency Relationships:A Laboratory Market Study,"Journal of Finance,1985,40, 809-820.Holt,Charles A.,"Industrial Organization:A Survey of Laboratory Research."In Kagel, John,and Alvin Roth,eds.,Handbook of Experimental Economics.Princeton:Princeton University Press,1995,349-443.Holt,Charles A.,"Classroom Games:Trading in a Pit Market,"Journal of Economic Perspectives,10(1),Winter1996,193-203.Holt,Charles A.and Roger Sherman,"Advertising and Product Quality on Posted-Offer Experiments,"Economic Inquiry,January1990,28(3),39-56.Lynch,Michael,Ross ler,Charles R.Plott,and Russell Porter,"Product Quality, Consumer Information and’Lemons’in Experimental Markets."In Pauline M.Ippolito and David Scheffman,Empirical Approaches to Consumer Protection in Economics,Washington, D.C.:Federal Trade Commission,1986,251-306.Miller,Ross M.,and Charles R.Plott,"Product Quality Signaling in Experimental Markets,"Econometrica,July1985,53(4),837-872.。
柠檬市场：质量的不确定性与市场机制
２００１年诺贝尔经济学奖得主—乔治·阿克洛夫经济学思想述评瑞典皇家科学院于10月10日宣布，将本年度诺贝尔经济学奖授予美国经济学家乔治·阿克洛夫、迈克尔·斯宾塞和约瑟夫·斯蒂格利茨，以表彰他们运用不对称信息理论研究市场经济所取得的成就。
众所周知，诺贝尔经济学奖认可的都是经过实践检验的理论成果，而经济学理论成果经过实践检验被认为是正确的，通常需要20、30年。
此次获奖三人的理论成果主要集中在20世纪70年代。
他们的获奖意味着国际上正式承认其理论具有广泛的应用价值。
瑞典皇家科学院在其新闻公报中称，许多市场都存在信息不对称现象：买卖的一方往往掌握比另一方更多的信息。
借款人比贷款人更了解自己的还贷潜力，企业经理和董事会比股民更了解企业的未来，客户比保险公司更了解他们发生事故的风险率。
而一个市场经济的有效运作，需要买者和卖者之间拥有充分的共同信息。
如果信息不对称现象非常严重，那么就有可能限制市场功能的发挥，在极端情况下，会使整个市场不存在。
此次获奖的三位经济学家分别从产品市场、劳动力市场、保险及资金市场等领域探讨了信息不对称问题，指出市场体制需要完善、设计。
这是对传统经济学的重大突破。
他们的研究揭示了当代信息经济的核心问题，奠定了关于市场经济不对称信息理论的基础，其分析理论用途广泛，既适用于对传统的农业市场的分析研究，也适用于对现代金融的分析研究。
本文主要是对乔治·阿克洛夫的一些主要经济思想进行简单的评述，以便大家更深刻地了解这位世界一流的经济学家。
一、乔治·阿克洛夫生平简介乔治·阿克洛夫(George A.Akerlof)1940年出生于美国康涅狄州纽黑文，现年61岁；1962年，在耶鲁大学获得学士学位；4年后在麻省理工学院获得博士学位。
他曾担任伦敦经济学院货币银行专业的经济学教授、经济顾问委员会高级经济学家、布鲁金斯小组(Brooking Panel)经济问题高级顾问和美国经济联合会副主席；现任加州大学伯克利分校经济学教授。
“柠檬”市场：质量不确定和市场机制
《“柠檬”市场：质量不确定性与市场机制》一、课堂讲解作者乔治·阿克洛夫的写作风格很鲜明，他喜欢用简单模型、简单事例说明重要的经济学问题。
他毕业于麻省理工大学，在学期间十分关注种族歧视问题、心理学以及人类学，他的这些关注点在文中也有一些体现，例如，少数民族就业、道德风险等。
我们在学习这篇文章时，不仅要了解作者观点，还要与前一篇文章《信息经济学》联系起来读。
其实无论阅读那篇经济学文章，我们都应该将文章中的理论与客观实际相联系，将文中理论放置于整个经济学框架中，带着全局观去看问题。
乔治从在引言中就阐明观点：质量不确定性光靠市场机制是无法解决的，还需要其他补充机制。
这其实就是一个假说，作者接下来要为自己的假说进行证实。
我们先关注这样几个问题：这篇论文的题目中“柠檬”是什么？柠檬就是低质量的商品；那什么是“柠檬”市场？它就是市场中充斥着低质量商品，而高质量商品不被交易的情形。
他首先举出一个二手车市场的例子。
二手车市场中汽车质量参差不齐，但由于买者在买车时无法区分汽车质量，所以无论高质量车还是“柠檬”出同样价格购买。
但卖者对汽车质量情况了于指掌，这就产生了信息不对称，此时卖者肯定先卖出质量低的车，高质量车根本不会卖出。
这样，低质量车就将高质量车逐出市场，最终二手车市场将不复存在。
这是为什么呢？因为低质量车会继而将质量较好、质量中等、质量再稍差的汽车依次逐出市场。
如图所示，一般来说，质量越好价格越高，但由于信息不对称，所有质量高于Q1的汽车，即质量差的车将质量高于Q1的车逐降到P2，同上次一样，质量在Q1到Q2之间的汽车逐出市无法成交，该市场最终不复存在。
本文还举出很多“柠檬”市场的例证。
如，保险，无论在哪一价格水平上，保险合同的购买者都有太多“柠檬”，导致保险公司的承担的过多本不应由它承担的风险，保险公司将不会继续开展此类保险业务；再如，少数民族就业问题，招聘公司由于不了解少数民族求职者的工作能力、社会背景、道德素质等方面信息，故为少数民族求职者提供同一薪酬，这使其中能力强者放弃进入该公司的机会，而能力弱者或许留在这个人才市场中寻找职位。
柠檬市场：质量的不确定性和市场机制(中英对照)
The Markets for “Lemons”:令狐采学Quality uncertainty and The Market Mechanism柠檬市场：质量的不确定性和市场机制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.（本文论述的是质量和不确定性问题。
现实中存在大量多种档次的物品给市场理论提出了饶有趣味而十分重大的难题）On the one hand, the interaction of quality differences and uncertainty may explain important institutions of the labor market.（一方面，质量差异和不确定性的相互作用可以解释劳动力的重要机制）On the other hand, this paper presents a struggling attempt to give structure to the statement: "Business in under-developed countries is difficult"; in particular, a structure is given for determining the economic costs of dishonesty.（另一方面，本文试图通过讨论获得这样的结论：在不发达国家，商业交易是困难的，其中，特别论及了欺骗性交易的经济成本）Additional applicationsof the theory include comments on the structure of moneymarkets, on the notion of "insurability," on theliquidity of durables,and on brand-namegoods.（本文的理论还可以用来研究货币市场、保险可行性、耐用品的流动性和名牌商品等问题）There are many markets in which buyers use some market statistic to judge the quality of prospective purchases.（在许多市场中，买者利用市场的统计数据来判断他们将要购买的商品的质量）In this case there is incentive for sellers to market poor quality merchandise, 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.（在这种情况下，卖者有动力提供低质量商品，因为某种商品的价格主要取决于所有同类商品质量的统计数据而非该商品的实际质量。
lecture two Lemon柠檬市场
12
Lemon Market
What are the costs of dishonesty?
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Lemon Market
List some examples of lemon market
14
Lemon Market
What is the equilibrium if q is uniformly is distributed on [0.2] if the utility function of group 2 is U2=M+3q? What is the equilibrium if q is uniformly is distributed on [t.3] giv en t>0?
6
Lemon Market
If the information of quality is symmetrically located or the s ellers are honest, what will happen in the lemon market? What is the welfare of society?
7
Lemon Market
If the information of quality is asymmetrically located or the sellers are dishonest, what will happen in the lemon market? What is the welfare of society? Suppose: All the cars are traded at the same price The quality of cars is uniformly distributed on the closed inte rval, [0,2] The buyers and sellers are both maximizers of expected utili ty
柠檬市场：质量的不确信性和市场机制中文版
【题名】"柠檬"市场：质量的不确信性和市场机制【作者】乔治·阿克洛夫【刊名】经济导刊.2001.000(006).-1-8【ISSN 】1004-8669【CN 】11-3053【馆藏号】97641X【关键词】信息经济学质量不确信性市场机制"柠檬市场" 信息不对称【分类号】F062.5一、引言本文论述的是质量和不确信性问题。
多种档次的物品给市场理论提出了有趣而又重要的问题。
一方面，质量不同和不确信性的彼此作用能够说明某些重要的劳动市场制度。
另一方面，本文力求对如下主张，即"在不发达国家做生意是因难的"给出一个模型．尤其是要给出一个用于确信不老实的经济本钱的模型。
理论的应用还包括对货币市场结构、不可保险性、耐用品的流动性和品牌产品的评论。
在许多市场中，购买者老是利用某些市场统计数据来判定欲购商品的质量。
在这种情形下，销售者就有动机销售劣质商品，因为从优质商品中受益的主若是其统计数据受阻碍的销售者整体而不是单个销售者。
结果是，产品的平均质量往往会下降，市场规模相缩小。
还应该看到的是，在这些市场中，社会收益和私人收益是有不同的，因此，在某些情形下，政府干与能够增加各方的福利。
或是，私人制度可能会产生，以利用各方潜在的福利增加。
可是，这些制度并非是孤立分散的(nonatomistic)、因此，权利的集中有可能形成一一这确实是制度本身带来的不良后果。
本文试图用汽车市场来论述上述思想。
应该强调的是，之因此选择汽车市场，是因为它超级具体而且易于明白得，而不是因为它的重要性或现实性。
二、以汽车为例的模型1．汽车市场旧车市场的例子说明了问题的本质。
用以说明这种现象的常见理由是，拥有一辆新车能够带来欢乐，而咱们却给出了另一种说明。
假定(为了说明问题，而不是现实情形)市场中只有4种汽车、即新车和旧车，好车和次品车(在美国，也称之为"柠檬")。
平狄克《微观经济学》(第7版)习题详解(第17章 信息不对称市场)
平狄克《微观经济学》（第7版）第17章信息不对称市场复习笔记跨考网独家整理最全经济学考研真题，经济学考研课后习题解析资料库，您可以在这里查阅历年经济学考研真题，经济学考研课后习题，经济学考研参考书等内容，更有跨考考研历年辅导的经济学学哥学姐的经济学考研经验，从前辈中获得的经验对初学者来说是宝贵的财富，这或许能帮你少走弯路，躲开一些陷阱。
以下内容为跨考网独家整理，如您还需更多考研资料，可选择经济学一对一在线咨询进行咨询。
1．质量不确定性和“柠檬”市场（1）旧车市场：柠檬问题阿克洛夫在1970年提出的分析旧车市场的“柠檬”（次货或二手货）模型，拉开了信息不对称在商品市场上应用的序幕，开创了逆向选择理论的先河：在旧车市场上，只有卖者知道车的真实质量，买者只知道车的平均质量，因而只愿意根据平均质量支付价格；而在一辆旧车的任一价格上，那些最差的次品车的主人最急于将他们的车出手；当买主把这些次品买回家后，才会逐渐发现它的缺陷；一段时间后，买主能够接受的旧车的平均价格会下降，那些持有缺陷最少的车的车主这时会认为还是将车留着自己用更为合算；这意味着，那些还留在市场上出售的汽车的平均质量又进一步降低了。
因此说，随着价格的下降，存在着逆向选择效应：质量高于平均水平的卖者会退出交易，只有质量低的卖者才会进入市场。
当产品的卖方对产品质量比买方有更多信息时，柠檬市场可能出现，使低质量商品驱逐高质量商品。
（2）不对称信息的含义不对称信息指市场上买卖双方所掌握的信息是不对称的，一方掌握的信息多些，一方掌握的信息少些。
包括两种情况：有些市场卖方所掌握的信息多于买方，商品市场和要素市场上都有这种情况；有些市场买方所掌握的信息多于卖方，保险与信用市场上有这种情况。
当购买者或者出售者交易时没有充分的信息来确定产品的真实质量，从而不同质量的产品以同一价格出售时，逆向选择就出现了。
结果，市场上就有太多的低质量产品和太少的高质量产品出售。
《“柠檬市场”质量的不确定性和市场机制》读书笔记
Akerlof ——《“柠檬市场”：质量的不确定性和市场机制》读书笔记本文试图将商品质量和不确定性联系在一起，考察不诚信行为的经济成本。
利用简单的均衡模型推导，在格雷欣法则基础上解释二手车柠檬市场中，买卖双方由于信息不对称最终导致市场消失的情况。
引言作者主要试图讲述本文的主要内容和观点：由于买家往往会通过市场统计数据得到对该市场中商品的预期质量，因此卖家就有降低自己产品质量浑水摸鱼的动机，但这样的想法最终会带来市场中整体商品质量的下降和市场规模的萎缩；社会回报不同于私人回报，因此政府干预以集中力量可能是有效的；选择汽车市场作为研究对象的原因；理论基础作者认为，“劣币驱逐良币”的格雷欣法则是基于买卖双方都知晓两种商品质量的基础之上的，而在二手车市场中，二手车的质量好坏只有卖方知道，买方只能评价市场的平均水平（如假设市场中好车的概率是q ），以相同的价格面对包含好车坏车的市场。
前提假设新车比旧车质量高——否则不会有二手车交易需求与供给函数：假设一个人对于二手车的需求强烈地依赖于汽车价格p 和二手车市场的平均质量 µ Q d =D(p,μ)而卖方对于二手车的供应和平均质量均取决于价格S =S(p)μ=μ(p)因此有：S(p)=D(p,μ(p))当价格下降平均质量也会下降，最终没有任何交易发生效用函数：假设有两组交易者，组1和组2，各自的效用函数分别为：U 1=M +∑x i n i=1U 2=M +∑32⁄x i n i=1此效用函数可以将买卖双方相区分，拥有二手车的边际效用高的组2即买方。
其中M 是除汽车以外的消费，x i 是i 车的质量对于该效用函数有几点假设基础假设：1.为使分析简便采取线性效用函数；2.U 的边际效用不变，即增加一辆车的消费带来的效用是相同的；3.消费者追求期望效用最大化；模型假设：4.交易者1拥有N 辆质量为x 并且服从均匀分布的汽车，交易者2没有汽车（这意味着1为卖方，2为买方）5.将其他商品M 的价格视为1信息不对称情况Y 为收入，则D 1=Y 1p ⁄，μp ⁄>1 ；D 1=0，μp ⁄<1表示当车的价值（质量）高于出价时，卖方组会收回所有汽车；当车的价值低于出价时，此时卖方卖车是获利的，因此会把旧车全都变卖，故需求为0。
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The Markets for “Lemons”:Quality uncertainty and The Market Mechanism柠檬市场：质量的不确定性和市场机制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.（本文论述的是质量和不确定性问题。
现实中存在大量多种档次的物品给市场理论提出了饶有趣味而十分重大的难题）On the one hand, the interaction of quality differences and uncertainty may explain important institutions of the labor market.（一方面，质量差异和不确定性的相互作用可以解释劳动力的重要机制）On the other hand, this paper presents a struggling attempt to give structure to the statement: "Business in under-developed countries is difficult"; in particular, a structure is given for determining the economic costs of dishonesty.（另一方面，本文试图通过讨论获得这样的结论：在不发达国家，商业交易是困难的，其中，特别论及了欺骗性交易的经济成本）Additional applications of the theory include comments on the structure of money markets, on the notion of "insurability," on the liquidity of durables, and on brand-name goods.（本文的理论还可以用来研究货币市场、保险可行性、耐用品的流动性和名牌商品等问题）There are many markets in which buyers use some market statistic to judge the quality of prospective purchases.（在许多市场中，买者利用市场的统计数据来判断他们将要购买的商品的质量）In this case there is incentive for sellers to market poor quality merchandise, 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.（在这种情况下，卖者有动力提供低质量商品，因为某种商品的价格主要取决于所有同类商品质量的统计数据而非该商品的实际质量。
结果，商品的平均质量将趋于下降，市场规模将不断缩小）It 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 welfare which can accrue to all parties.（我们还可以观察到在这种市场上，对个人和社会有不同的回报，因此，某种情况下，政府的干预可以增进社会的总体福利水平。
或者说，私人组织利用了整个社会福利水平潜在的增长机会而使自己获利）By nature, however, these institutions are nonatomistic, and therefore concentrations of power- with ill consequences of their own-can develop.（实际上，这些私人组织的行动所产生的影响并非可以忽略不计，因此，尽管集权本身有许多负面影响，但是，一定程度上的集权可以保证经济的健康发展）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，我们用汽车市场作为例子来阐释和进一步发展以上的思想。
需要指出的是，之所以选择旧车市场来讨论，是因为这个例子很具体，并且容易理解，而不是因为它的重要性和有何现实意义）二、以汽车市场模型为例（一）汽车市场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 lunch table justification for this phenomenon is the pure joy of owning a "new" car.（旧车市场的例子可以抓住问题的本质。
人们不止一次的听说或惊讶于新车与刚刚开出样品陈列室的汽车之间的价格存在巨大差别。
对于这种情况最普遍的解释是人们有一种对“新”车的特别偏好）We offer a different explanation. Suppose (for the sake of clarity rather than reality) that there are just four kinds of cars. There 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.（假设（作出这种假设只是为了简化分析，而非从实际出发）用四种汽车：新车和旧车；高质量的车和低质量的车（低质量的车在美国被称为“柠檬”）。
一辆新车可能是高质量的，也可能是“柠檬”，当然一辆旧车也同样有两种情况）The individuals 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 lemons.（在这样的市场上，消费者买新车时并不知道车辆到底是高质量的还是“柠檬”，但是他知道这辆车是高质量的概率是q，是“柠檬”的概率是“1-q”。
这里假设q是高质量车占所有汽车的比率，1-q是“柠檬”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 is a lemon. This estimate is more accurate than the original estimate.（车主在拥有汽车后一段时间内就会了解到该车的质量，也就是说，此时车主可以赋予该车可能是“柠檬”的一个概率值，这个估计比初始的估计更加准确）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 cars 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，信息不对称发生了：卖主掌握了比买主更多的关于汽车质量的信息。