1、1 中文 2220字， 1440单词 外文原稿一： The Market for “Lemons”: Quality Uncertainty and the Market Mechanism By George A. Akerlof Publication: The Quarterly Journal of Economics, 1970,84 (3)： 488-500. I. Introduction This paper relates quality and uncertainty. The existence of goods of many grades poses interest
2、ing 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 underdevel
3、oped 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
4、 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 i
5、ndividual 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
6、 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 nonatomistic, and therefore concentrations of power -with ill consequences of their own -can develop. The automobile market
7、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. 2 . THE MOBEL WITH AUTOMOBILES AS AN EXAMPLE A. The Automobiles Market The example of us
8、ed 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. We offer a d
9、ifferent 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 use
10、d 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
11、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
12、 in available information has developed: for the sellers now have more knowledge about the quality of a car than the buyers. But good can 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
13、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
14、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. Greshams law has made a modified reappearance. For most cars traded will be the lemons, and good cars may not be traded at all. The bad cars tend to dri
15、ve out the good (in much the same way that bad money drives out the good). But the analogy with Greshams law is not quite complete: bad cars drive out the good because they sell at the same price as good can； similarly, bad money drives out good because the exchange rate is even. But the bad cars se
16、ll 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 Greshams law, however, presumably both buyer and seller can tell the difference between good and bad money. So the analogy is instructive, but not compl
17、ete. 3 n U2= M+ 3 / 2xi i=1 B. Asymmetrical Information It has been seen that the good cars may be driven out of the market by the lemons. But in a more continuous case with different grades of goods, even worse pathologies can exist. For it is quite possible to have the bad driving out the not-so-b
18、ad 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 trade
19、d, or Q d = D (p, ). Both the supply of used cars and also the average qualitywill depend upon the price, or = (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). As the price falls, normally the quality will also fall. And it is
20、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 function. Where M, is the consumption of goods other than automobiles, xi, is the quality
21、 of the ith automobile, and n is the number of automobiles. Similarly, let Where M, xi ,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
22、 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
23、 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 von Neumann-Morgenstern maximizers of expected utility； (2) that group one has N cars with n U1=M+ xi i=1
