柠檬市场：质量的不确定性与市场机制
“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。
信息市场均衡的实际例子
信息市场均衡的实际例子“柠檬”在美国俚语中表示“次品”或“不中用的东西”所以，柠檬市场(The Market for Lemons)也称次品市场。
1970年，31岁的著名经济学家乔治·阿克洛夫发表了《柠檬市场：质量不确定和市场机制》的论文，对柠檬市场进行了具体分析，所以，柠檬市场也称阿克洛夫模型。
对于柠檬市场，主流的结论是：由于信息不对称，往往好的商品遭受淘汰，而劣等品会逐渐占领市场，从而取代好的商品，导致市场中都是劣等品，并最终导致市场消亡。
其分析的思路是：柠檬市场由于交易一方并不知道商品的真正价值，只能通过市场上的平均价值来判断平均质量，由于难以分清商品好坏，因此也只愿意付出平均价格。
由于商品有好有坏，对于平均价格来说，提供好商品的自然就要吃亏，提供坏商品的便得益。
于是好商品便会逐步退出市场。
由此导致市场商品平均质量下降，于是平均价格也会进一步下降，最后市场就只剩下坏商品。
对于上述分析思路，研究者往往通过举旧车市场的例子来进一步验证分析结论。
比如，有研究者做如下分析 ：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30万元，质量较差的价值10万元（尽管经过维修，换新后）。
二手车市场的特性是卖方（经销商或原车主）知道自己的车是好车或坏车，但买方在买卖交易时无法分辨。
在买方无法确知车子的好坏时，聪明的卖方知道，无论自己手中的车是好车还是坏车，宣称自己的车是为“好车”一定是最好的策略（反正买方无法分辨）。
尽管市场中有一半好车、一半坏车。
但如果你去问车况，卖方必有一个统一的答案——我们的车是好车。
但消费者真的会以好车的价格向卖方买车吗？不会！买方知道，他买的车有一半几率是好车、有一半几率是坏车，因此最高只愿出价20万元（20=10×1/2+30×1/2）买车。
此时进一步发生的事情是，市场拥有的好车的原车主开始惜售，一台30万元的好车却只能卖到20万元，有一些车主宁愿留下自用，亦不愿忍痛割爱，因此好车逐渐退出市场。
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：质量不确定性与市场机制
柠檬市场：质量不确定性与市场机制乔治•阿克洛夫1.引言本文着重讨论质量和不确定性问题。
现实中大量存在的商品异质性使传统的市场理论面临着饶有趣味而又十分重大的难题，一方面，质量的差异和不确定性之间的相互作用可以解释劳动力市场上的重要机制，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，将特别论及欺骗性交易的经济成本。
本文的理论还可以用来研究倾向市场、保险可行性、耐用品的流动性和名牌商品等问题。
在许多市场中，买者利用市场的一些统计数据来判断他们将要购买的商品的质量。
在这种情况下，卖者就有动力提供低质量的商品因为某种质量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取决于该商品的实际质量。
结果，商品的平均质量将趋于下降，市场规模将不断缩小。
我们还可以观察到这种市场对个人和社会有不同的回报，因此，在某种情况下，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。
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。
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。
2.作为例证的汽车市场模型2.1汽车市场旧车市场的例子可以抓住问题的本质。
人们不止一次地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。
对这种情况最普通的解释是人们有一种对“新”车的特别的偏好。
在此我们提出一种与众不同的解释。
假设（作出这个假设是为了使问题更加简单明了，而并非从现实出发）有4种汽车：新的和旧的，高质量的和低质量的。
低质量车在美国被称为“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这两种情况。
在这样的市场，消费者买一辆新车时并不知道这辆车到底是高质量的还是“柠檬”，但是他知道这辆车是高质量车的概率是q，是“柠檬”的概率是)-。
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。
2023年柠檬行业市场调研报告
2023年柠檬行业市场调研报告一、行业概述柠檬是一种常见的水果，具有丰富的维生素C、类黄酮、柠檬酸、柠檬皮素等营养成分，在烹饪、医药、保健等领域都有很高的价值。
目前全球柠檬产量最高的国家有印度、巴西、中国、美国等。
我国柠檬种植主要集中在云南、四川、广东等地。
二、市场现状1.国内市场前景广阔随着人们健康意识的提高和生活水平的提升，柠檬作为一种富含营养的水果，更加受到人们的关注。
而中国的柠檬产量逐年增加，市场规模也在不断扩大。
近年来，柠檬的加工和深加工应用日益增多，市场发展潜力巨大。
2.国际市场需求大全球范围内，柠檬的需求量越来越大，主要应用于制作果汁和食品。
其中，美国市场需求量最大，占全球市场份额的44%以上。
巴西、墨西哥、中国等也是世界上柠檬的主要出口国家和地区之一，我国柠檬出口量逐年增加，出口市场呈扩大趋势。
3.市场价格波动柠檬的价格受多种因素影响，包括天气、季节、供给和需求等。
近年来，柠檬的价格波动较大，价格也有所上涨，主要由于柠檬产量下降、市场需求增加等因素引起。
目前，柠檬的价格较为稳定，但仍有一定的不确定性。
三、市场机遇1.农业精准扶贫在国家农业精准扶贫政策的推动下，柠檬种植可以成为一种重要的扶贫产业，为农村地区带来更多的经济效益。
同时，柠檬的加工、深加工等产业也可以带动农村产业发展，带来更多务工机会，促进农村经济全面发展。
2.市场需求增加随着人们生活水平的提高和健康意识的增强，柠檬作为一种天然的营养食品，其需求量也在不断增加。
尤其是在柠檬加工、深加工领域，市场潜力巨大，可以为企业带来更多的商机。
3.技术创新提升产量随着科技的不断进步，柠檬种植技术也在不断发展。
通过在柠檬新品种培育、生产技术等方面的持续创新，可以提升柠檬的产量和品质，满足市场需求，推动柠檬产业发展。
四、市场挑战1.市场竞争加剧柠檬产业的竞争主要来自于生产和销售端，尤其是在果品期间，供应量增加，市场竞争加剧。
同时，柠檬种植和深加工技术也是市场竞争的重要因素。
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。
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。
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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。
他的理论研究范围集中在金融市场、宏观经济学、货币政策、贫困和失业以及种族歧视、犯罪、家庭问题等，在这些领域都发表了大量的研究文献，最引人注目的是他的不完全信息论。
他于1970年发表的论文《“柠檬”市场：质量不确定性和市场机制》首先提出信息不对称和逆向选择，与斯蒂格利茨(Joseph Stiglitz)被并称“不完全信息经济学之父”。
他的这篇文章具有典型的开创性特点，介绍了一种简单但深刻且普遍的观点，并对无数有趣的观点进行了广泛的运用，成为信息经济学最重要的文献之一，也奠定了他获得此次诺贝尔经济学奖的基础。
如今，阿克洛夫关于逆向选择的深刻见解被普遍应用于本科生日常微观经济学课程的教学中，这足以显示其影响之深远。
近20年来，他对失业问题的研究成果也十分突出。
二、“柠檬”市场理论：不完全信息论传统经济学认为，市场是万能的，通过自由竞争可以实现资源的合理配置。
但是，这是以市场交换无摩擦为假定前提的。
而越来越多的人在经济生活中发现，由于信息不对称现象的存在，自由竞争的市场未必能带来最高的效率。
所谓信息不对称性，是指契约关系的一方(如代理人)在某些方面掌握着“私人信息”，这些信息只有他自己最了解；另一方则不了解。
而造成信息不对称性的原因是不确定性以及社会劳动分工和专业化发展。
社会劳动分工使信息差别的程度加深，产生不同的信息优势和信息劣势；而信息优势和信息劣势的出现，意味着信息不对称性的存在。
专业化使得个人在其自身的专业领域比其他专业领域的个人了解更多的专业知识，从而导致了专业与非专业性信息优势与劣势。
市场上广泛存在的信息不对称现象引起了阿克洛夫的关注，他是第一个对存在所谓“逆向选择”信息问题的市场进行正式分析的学者，解释了信息不对称可以如何引起市场的逆向选择。
当汽车卖者或买者拥有不完全信息时，具有较低偿付能力的买者或较低质量车子的卖者，就会因此把市场中的其他人挤掉，阻止互利交易的存在。
他就此得出了“市场放开并不能解决所有问题，信息是有价值的”的结论。
在《“柠檬”市场：质量不确定性和市场机制》(The market for “lemons”:quality uncertainty and market mechanism)的论文中，阿克洛夫分析了一个卖者比买者更加了解产品特性的产品市场，并以旧车为例对此进行了经典分析。
在旧车市场上，既定的旧车卖者和关心车子质量的买者之间存在着信息不对称。
已经在车行里工作多年的卖者对旧车的性能、保养程度或损坏程度了如指掌，而买者却无从得知这些信息。
阿克洛夫把这种市场描述为“柠檬”市场，把旧车比喻为“柠檬”。
从此，“柠檬”(有缺陷的车子的口语用词)就成了每位经济学家词汇中一个众人熟知的比喻说法。
阿克洛夫认为，买者常常必须依赖各种近似估计的技巧，使他们能从有形到无形作出推断。
如果对一辆虽有少许凹坑和划痕但装饰很好的汽车和一辆明显破旧的汽车进行比较，买者可能会推断前者比后者保养得好，据此估计汽车的技术可靠性。
然而，大多数人很快意识到这种推断是犯了Ⅰ型错误(指在统计检验中不接受正确的零假设)，即提出了错误的主张，认为一辆漂亮的车等于一辆好车。
于是，涉及一些更重要的交易方面，消费者根据可靠性等近似估计技巧推测对一辆旧车作出的报价，可能会比那些知道旧车前主人如何小心翼翼地保养这辆车的人要来得低。
人们会预料到市场上的汽车外表华丽，但保养不当或有瑕疵。
如果购车者是个风险中性者，在他不能确知所购车辆的内在价值的前提下，他愿意接受的价格也只是所有旧车价值按概率加权计算的一个平均值，即预期价格，而不管购得的旧车质量如何。
结果，过了一段时间，这种预测增加了买者对产品质量的不确定性，进一步降低了合理的报价。
随着时间的流逝，买者通过经验发现卖者把低于中等水平的产品投入市场，这种认为产品质量递减的意识反过来又会使产品的价格下降。
这一过程不断持续，最后市场上只剩下损坏最严重的旧车，所有稍好一点的旧车都会从市场上消失。
阿克洛夫用一个简单的例子来说明他的观点。
假设一种产品以不可分割的单位进行买卖，并且具有固定比例λ和1－λ的低和高两种质量。
每个买者潜在地有兴趣购买一辆汽车，但在购买时无法识别两种质量之间的区别。
所有的买者对两种质量作出相同的估价：对买者来说低质量的车值WL美元，而高质量的车值WH美元，且WH>WL。
每个卖者了解他所卖的汽车的质量，评价低质量汽车的价格为VL美元(VL<WL)，而高质量汽车的价格为VH美元(VHW(W=λWL＋(1－λ)WH)。
如果贸易在这种条件下发生，买者的(理性)质量预期将会严格地为W。
换句话说，市场价格不可能超过W(假定消费者是风险厌恶者或风险中性者)。
高质量产品的卖者就会因此退出市场，仅留下低质量产品的这种逆向选择。
阿克洛夫另一个重要的深刻见解，是认为经济主体有强烈的动力去抵消有关市场效率信息问题的逆向效应，许多市场机制可以被认为是在试图解决不对称信息问题中出现的。
他主张防止市场失败的方式，是找到某种传递商品真实价值既便宜又可靠的方法。
如仅仅与亲戚朋友交易；提供证明合格的服务记录；通过长期的努力建立品牌让消费者认同；通过设立连锁店建立信誉；在交易中提供担保；等等。
他在论文中总结道：“这(逆向选择)可能解释许多经济制度”。
这种预言已经成为现实，他成为分析经济制度如何缓和不对称信息后果的重要工具。
在很多情况下，持有个人信息的各方会发现要安排高效率的交易是困难的，甚至是不可能的。
不完全信息的介入者一般是作为对策设计者，会影响双方之间的信息流动，促成协议，在某些情况下还实际决定问题的最终解决(例如，有约束力的仲裁)。
实际上，介入者创造一种双方必须参与的对策游戏。
因此，任何介入理论都必须与设计具有满意的均衡结局的对策游戏联结在一起。
阿克洛克指出，如果介入者只能起旁听者的作用，而且如果不能使对策游戏的结局取决于双方的实际型，那么事后的低效率就是不可避免的。
这种理解导致了“效率刺激机制设计”理论的发展。
阿克洛夫在他的文章中，不仅解释了私人信息可能如何导致市场发生功能障碍，而且指出这种信息不对称出现的频率以及它们产生的深远后果。
他指出类似的信息不对称性具有普遍性和重要性，例子之一就是劳动力市场的社会分离和老年人购买个人医疗保险的困难。
他认为，这种理论尤其适用于发展中国家，可解释其市场上借款率猛升的原因。
他的逆向选择例子之一就是来自20世纪60年代印度乡村的借贷市场。
在这个市场上，当地货币借贷者收取两倍于大城市的利率。
但是，一个试图在这两个市场上套利的投机者，在不了解当地借款者信用的情况下，贷款给偿付能力较差的人将会冒一定的风险，从而有可能遭受重大的损失。
他还用信息不对称理论分析了证券市场的情况，认为证券市场上同样存在信息不对称现象。
在证券市场上，投资者和证券发行商关于证券质量的信息经常存在巨大差异。
债务人比未来的债权人拥有更多关于债券安全性的信息。
这种信息不对称的结果是未来投资者愿意报出一个假定证券仅有某种未履行责任平均风险的价格。
在这个市场上，质量不确定性的必然结果是，低质量证券的卖者将获利较多，而高质量的卖者获利较少。
这种市场不完全性的标准疗法就是可靠的信息。
此外，阿克洛夫在《等级经济学、无休止的激烈竞争和其他可悲的陈述》(1976)一文中，对诸如等级制度、工厂工作条件和分佃制等极不相同情况下信息不对称的重要性进行了更为全面的讨论。
他使用图解的例子表明所谓的“指标”的某种变量不仅提供了如何提高效率的重要经济信息，而且可能如何导致经济陷入不合意的均衡。
在分佃制的例子中，地租用收成的固定比例来偿还，承租人的产量作为他工作努力程度的一个指标。
在工厂的装配线上，传送带的速度作为工人能力的指标，因而可以作为区分不同能力的工人之间的一种手段。
三、劳动力市场理论：效率工资论除了对不对称信息的研究以外，阿克洛夫在用社会学和社会人类学的观点丰富经济理论方面也具有独创性。
他在已发表的若干篇关于劳动力市场问题研究的论文中，考察了诸如对雇主的“互惠”和对同事的“公平”等感情可能如何导致更高的工资以及由此产生的失业。
实证研究也支持了他的感情刺激观点。
在20世纪60年代晚期，凯恩斯主义占支配地位的时代结束以后，宏观经济发展的困扰之一是许多新观点无法解释失业，因为在大多数经济模型中，供给等于需求即产生均衡。
如果这种相等在劳动力市场也成立的话，那么就不存在非自愿失业了。
阿克洛夫用劳动力市场的效率模型解释了为什么会出现劳动力市场均衡，雇主愿意支付比市场出清工资更高的工资，从而解释了非自愿失业。
他指出，在劳动力市场上雇主和求职者关于求职者信息的不对称性，使得企业只能通过许诺高工资来挑选高素质的员工，从而提高整体工作效率。