2007年6月5日 网上拍卖的经济学

你也许会认为，如果说有一件事经济学家应该能告诉你如何去做，那就是在拍卖网站eBay上成功登记拍卖物品。毕竟，拍卖理论家在这行享有盛名；其中一位拍卖理论家苏珊o阿西(Susan Athey)在今年4月赢得了约翰o贝茨o克拉克(John Bates Clark)经济学奖章。（克拉克奖章获得者还有保罗o萨缪尔森(Paul Samuelson)、约瑟夫o斯蒂格利茨(Joseph Stiglitz)和史蒂文o莱维特(Steven Levitt)，比诺贝尔奖(Nobel)获奖者还要罕见。）

You might think that if there's one thing an economist should be able to tell you how to do, it's successfully list an item on the auction website eBay. Auction theorists are, after all, celebrated in the profession; one of them, Susan Athey, won the John Bates Clark medal in April. (Clark medallists, who include Paul Samuelson, Joseph Stiglitz and Steven Levitt, are scarcer than Nobel laureates.)

然而，尽管拍卖理论已经很发达，但其预测容易受到现实中一些波澜的影响。比如说，标准经济学假设人是理性的，这种假设通常是对的：在啤酒价格上涨时，多数人都会少喝一些啤酒。不过，拍卖要求有"如果他认为她认为我认为他那么认为"的推理链条，而这种链条往往存在薄弱环节。如果任何出价方有任何理由怀疑其他出价方是不理性的，那么，这些环节就会轻易断裂。

Yet although the theory of auctions is well-developed, its predictions are sensitive to wrinkles in reality. For example, the standard economic assumption that people are rational is usually a good one: when the price of beer rises, most people drink less beer. But auctions require "if he thinks that she thinks that I think that he thinks" chains of reasoning that tend to have weak links. Those links can easily break if any bidder has any reason to suspect that any other bidder is irrational.

另一个理论难题是进入拍卖。多数拍卖理论家假定有固定人数的拍卖方存在，他们全都准备好了要出价。不过，虽然经济学家可以假设出价方存在，eBay的卖方却不得不去吸引这些人。

Another theoretical conundrum is entry to the auction. Most auction theorists assume a fixed number of bidders, all poised and ready to bid. But while economists can assume bidders into existence, eBay sellers have to go out and hook them.

这不是拍卖理论的一个微小疏忽。为移动电话运营商举行的大规模"3G"拍卖背后的经济学家--保罗o克伦佩雷尔(Paul Klemperer)已经表明，一场拍卖中看似微不足道的特点可能会让出价方却步，造成巨大（和灾难性的）影响。出于这些和其它原因，明智的拍卖理论家在没有充分了解整个背景的情况下，会避免预测某个具体的拍卖计划会有什么效果。

This is no minor oversight of auction theory. Paul Klemperer, one of the economists behind the massive "3G" auctions for mobile phone operators, has shown that trivial-seeming features of an auction can have big (and disastrous) effects by repelling bidders. For these reasons and others, wise auction theorists would avoid predicting how a specific auction design will work without knowing much more about the context.

对经济学家来说，幸运的是，eBay不仅提出了问题，也给出了解决办法。由于每天都有数不胜数的拍卖开拍，这个拍卖网站提供了大量数据。如果可以公开获得的数据不够用，还可以很容易地进行"现场"实验，在出价方的自然生活环境中研究他们。

Fortunately for economists, eBay offers solutions as well as problems. With hundreds of thousands of auctions starting every day, the auction site provides masses of data. And if the publicly available data isn't enough, it's also easy to conduct an experiment "in the field", studying bidders in their natural habitat.

亚利桑那大学(University of Arizona)经济学家戴维o赖利(David Reiley)自eBay出现之前就一直在研究网上拍卖。在最近与拉玛o卡特卡尔(Rama Katkar)合著的一篇论文中，他对eBay拍卖中的保留价格应该公开还是保密的问题进行了研究。

David Reiley, an economist at the University of Arizona, has been studying online auctions since before eBay existed. In a recent paper with Rama Katkar, he investigated whether reserve prices in eBay auctions should be open or secret.

拍卖理论提出一种看法，认为保留价格保密更好。保留价格保密可以让出价方看到彼此逐渐攀升的出价，从而激起他们的信心，让他们相信自己不是唯一欣赏这件物品的人。即便出价太低、达不到保留价的水平，它们也能达到一个重要目的--安抚出价方，让他们知道其他人也感兴趣。在eBay上公开保留价格就不可能起到这种安抚作用了；任何人都不能提交低于公开保留价格的出价，而没有任何来自其他出价方的信心信号，就可能出现没有人出价高出保留价的危险。

Auction theory offers an argument that a secret reserve price is better. A secret reserve price allows bidders to see each others' gradually ascending bids and thus draw confidence that they are not alone in prizing the item. Even though the bids are too low to beat the reserve, they serve an important purpose of reassuring bidders that others are also interested. An open reserve price on eBay makes that reassurance impossible; nobody can submit a bid below the open reserve, and lacking any signs of confidence from other bidders, there is a danger that nobody may submit a bid above it either.

要判断这种理论观点在实践中是否真的有价值，有太多不可精确估量的因素。因此，卡特卡尔和赖利通过拍卖50对匹配的收藏卡片对这个理论进行了检验。他们的方法是，在保留价相同的情况下，一半公开保留价，一半保密保留价。他们的结论与这种理论观点截然相反：保密的保留价达不到预期目的。它们不是激发出价方的兴趣，反而似乎是让他们退却，这也许是因为他们担心，保留价之所以保密，是因为它高得离谱。由于不想浪费自己的时间，许多出价方就会点击浏览器上的"返回"键，再找别的地方出价。

There are too many imponderables to tell whether this theoretical argument is what really counts in practice. So Katkar and Reiley put the theory to the test by simply selling 50 matched pairs of collectible cards, half with an open reserve price and half with a secret reserve price of the same level. Their conclusion, contrary to the theoretic argument, is that secret reserve prices are counterproductive. Far from stimulating interest they seem to put off bidders,who perhaps fear that a secret reserve is secret because it is far too high. Not wishing to waste their time, many of them just click "back" on their browsers and find somewhere else to bid.

这个结论也许不会撼动世界，但方法非常重要。戴维o赖利是最早发现互联网正在生成大量可研究数据的经济学家之一。如今，eBay、亚马逊(Amazon)到Match.com等众多网站提供的这种数据，正在丰富经济学研究。它可能也会让少数eBay拍卖方富起来。

The conclusion may not shake the world but the method is important. David Reiley was one of the first economists to realise that the internet was generating vast amounts of researchable data. Now that data, from sites ranging from eBay and Amazon to Match.com, is enriching the study of economics. It may enrich a few eBay sellers, too.

蒂姆o哈福德的著作《卧底经济学家》(The Undercover Economist)（小布郎出版社(Little, Brown)）目前已经出版平装本。

Tim Harford's book "The Undercover Economist" (Little, Brown) is out now in paperback.