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经济学人文艺新闻在线试听:信息不对称之柠檬市场理论与效应(下)

比目鱼 于2017-01-12发布 l 已有人浏览
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Signalling explains all kinds of behaviour.Firms pay dividends to their shareholders, who must pay income tax on the payouts.Surely it would be better if they retained their earnings, boosting their share prices, and thus delivering their shareholders lightly taxed capital gains.Signalling solves the mystery: paying a dividend is a sign of strength, showing that a firm feels no need to hoard cash.By the same token, why might a restaurant deliberately locate in an area with high rents?It signals to potential customers that it believes its good food will bring it success.

Signalling is not the only way to overcome the lemons problem.In a 1976 paper Mr Stiglitz and Michael Rothschild, another economist, showed how insurers might “screen” their customers.The essence of screening is to offer deals which would only ever attract one type of punter.Suppose a car insurer faces two different types of customer, high-risk and low-risk.They cannot tell these groups apart; only the customer knows whether he is a safe driver.Messrs Rothschild and Stiglitz showed that, in a competitive market, insurers cannot profitably offer the same deal to both groups.

If they did, the premiums of safe drivers would subsidise payouts to reckless ones.A rival could offer a deal with slightly lower premiums, and slightly less coverage, which would peel away only safe drivers because risky ones prefer to stay fully insured.The firm, left only with bad risks, would make a loss.(Some worried a related problem would afflict Obamacare, which forbids American health insurers from discriminating against customers who are already unwell: if the resulting high premiums were to deter healthy, young customers from signing up, firms might have to raise premiums further, driving more healthy customers away in a so-called “death spiral”. )

The car insurer must offer two deals, making sure that each attracts only the customers it is designed for.The trick is to offer one pricey full-insurance deal, and an alternative cheap option with a sizeable deductible.Risky drivers will balk at the deductible, knowing that there is a good chance they will end up paying it when they claim.They will fork out for expensive coverage instead.Safe drivers will tolerate the high deductible and pay a lower price for what coverage they do get.

This is not a particularly happy resolution of the problem.Good drivers are stuck with high deductibles—just as in Spence's model of education, highly productive workers must fork out for an education in order to prove their worth.Yet screening is in play almost every time a firm offers its customers a menu of options.Airlines, for instance, want to milk rich customers with higher prices, without driving away poorer ones.If they knew the depth of each customer's pockets in advance, they could offer only first-class tickets to the wealthy, and better-value tickets to everyone else.But because they must offer everyone the same options, they must nudge those who can afford it towards the pricier ticket.That means deliberately making the standard cabin uncomfortable, to ensure that the only people who slum it are those with slimmer wallets.

Adverse selection has a cousin.Insurers have long known that people who buy insurance are more likely to take risks.Someone with home insurance will check their smoke alarms less often; health insurance encourages unhealthy eating and drinking.Economists first cottoned on to this phenomenon of “moral hazard” when Kenneth Arrow wrote about it in 1963.Moral hazard occurs when incentives go haywire.The old economics, noted Mr Stiglitz in his Nobel-prize lecture, paid considerable lip-service to incentives, but had remarkably little to say about them.In a completely transparent world, you need not worry about incentivising someone, because you can use a contract to specify their behaviour precisely.It is when information is asymmetric and you cannot observe what they are doing (is your tradesman using cheap parts? Is your employee slacking? ) that you must worry about ensuring that interests are aligned.

Such scenarios pose what are known as “principal-agent” problems.How can a principal (like a manager) get an agent (like an employee) to behave how he wants, when he cannot monitor them all the time?The simplest way to make sure that an employee works hard is to give him some or all of the profit.Hairdressers, for instance, will often rent a spot in a salon and keep their takings for themselves.But hard work does not always guarantee success: a star analyst at a consulting firm, for example, might do stellar work pitching for a project that nonetheless goes to a rival.So, another option is to pay “efficiency wages”.

Mr Stiglitz and Carl Shapiro, another economist, showed that firms might pay premium wages to make employees value their jobs more highly.This, in turn, would make them less likely to shirk their responsibilities, because they would lose more if they were caught and got fired.That insight helps to explain a fundamental puzzle in economics: when workers are unemployed but want jobs, why don't wages fall until someone is willing to hire them?An answer is that above-market wages act as a carrot, the resulting unemployment, a stick.And this reveals an even deeper point.

Before Mr Akerlof and the other pioneers of information economics came along, the discipline assumed that in competitive markets, prices reflect marginal costs: charge above cost, and a competitor will undercut you.But in a world of information asymmetry, “good behaviour is driven by earning a surplus over what one could get elsewhere,” according to Mr Stiglitz.The wage must be higher than what a worker can get in another job, for them to want to avoid the sack; and firms must find it painful to lose customers when their product is shoddy, if they are to invest in quality.In markets with imperfect information, price cannot equal marginal cost.

The concept of information asymmetry, then, truly changed the discipline.Nearly 50 years after the lemons paper was rejected three times, its insights remain of crucial relevance to economists, and to economic policy.Just ask any young, black Washingtonian with a good credit score who wants to find a job.

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