"Your money or your life." The choice traditionally presented by the highwayman is supposed to have only one sensible answer. Money is, after all, no use to a corpse. Yet economists often study something rather like the highwayman's offer in an attempt to uncover the answer to an important question: how much is your life actually worth?

Like many awkward questions, this is one that has to be answered. Safety regulations save lives but also raise the cost of doing business, a cost we all pay through higher prices. Are they worth it? Our taxes pay for life-saving spending on road safety and fire fighting. Are they high enough, or too high?

So how much are we willing to spend to save a life? A traditional planner's approach used to be to measure the value of wages lost due to death or injury. That's dreadful: it confuses what I think my life is worth with what my boss thinks my life is worth.

So an alternative is to ask people how much they would pay for a safer car or kitchen cleaner. But such surveys do not always produce sensible results. Our answers depend on whether we're being offered a safer ?10 household cleaner and then asked if we want the more dangerous ?5 version, or whether we're offered the ?5 brand and then asked if we'll pay ?10 for the safer product. People often answer "no" to both questions, contradicting themselves. These inconsistencies mean that we're either irrational or lying to pollsters, and perhaps both.

Economists therefore tend to prefer observing real choices. If you're willing to cross a busy street to pick up a ?20 note, the economist who put it there can infer something about your willingness to accept risk. More orthodox approaches look at career choices: if you're willing to be a lumberjack, part of that decision is to accept risk in exchange for financial reward.

Being a soldier is risky; so is being a drug-dealer or prostitute. The difficulty, evidently, is to disentangle the health risk and the financial reward from all the other motivations to choose a particular way of life. That isn't easy but economists try.

World Bank economist Paul Gertler and his colleagues reckoned that Mexican prostitutes valued their lives at about $50,000 per year, based on willingness to take money not to use condoms. At five times their annual earnings, that's a similar figure to workers accepting risky jobs in rich countries.

There are anomalies. Steve Freakonomics Levitt and sociologist Sudhir Venkatesh calculated that Chicago drug dealers seemed to value their entire lives at $50,000 to $100,000 - low indeed, even for poor young men whose career choice indicates a taste for risks.

Whatever the frailties of these calculations, they are the best we have. And far from cheapening life, this sort of research often highlights just how valuable our safer, healthier modern lives really are. Kevin Murphy of the Chicago Graduate School of Business recently visited London to present his research on the value of health improvements in the US since 1970. They're vast - about $10 trillion in today's money. Looking further back, if you had to choose between the material progress of the 20th century and the improvements in health, it would be a toss-up. The health gains are as valuable as everything else put together. Encouragingly, health in most developing countries has improved faster than in rich ones, suggesting that global inequality is falling.

And a more personal piece of good news: Murphy reckons the delicious cheeseburger I ate before interviewing him only cost me ?1 worth of health. Talk about a good deal.

"要钱还是要命。"这个通常由劫匪提出的选择，理应只有唯一明智的答案。毕竟，钱对死人来说是没用的。然而，经济学家们经常研究一些与劫匪的提议非常相似的东西，以揭示一个重要问题的答案：你的生命到底值多少钱？

与许多棘手的问题一样，这是个必须回答的问题。安全规章能够拯救生命，但也会提高经营成本，而这是一个我们通过更高的价格、都需要支付的成本。它们真的物有所值吗？在道路安全和消防安全方面，我们缴纳的税款，用作了拯救生命的支出。它们是否足够高，或者是过于高昂了呢？

那么，为了拯救一条生命，我们愿意花费多少呢？一种传统计划者的方法，曾是衡量死亡或受伤所导致工资损失的价值。这十分可怕：它混淆了我心目中自己生命的价值，与我老板心目中我生命的价值。

因此，另外一种选择，就是询问人们愿意为安全程度更高的汽车或厨房洗洁精支付多少钱。但是，这种调查并不总能得出明智的结论。我们的回答取决于，是否为我们提供了一种更为安全的、价值10英镑的家用洗洁精，然后问我们是否想要一个更为危险的、价值5英镑的产品；或者，是否向我们提供了售价5英镑的品牌，然后问我们是否将为更安全的产品支付10英镑。人们对上述两个问题的回答往往都是"不"，这使他们自相矛盾。这些矛盾意味着，我们要么是缺乏理性，要么是在对调查者撒谎，或者两者兼而有之。

因此，经济学家们往往更愿意去观察真实的选择。如果你愿意横穿一条繁忙的街道，去捡一张20英镑的纸币，把钱放在那里的经济学家可推断出一些与你承受风险的意愿有关的东西。更为正统的方法着眼于职业选择：如果你愿意当一名伐木工人，这个决定的一部分，便是承受风险，以此换取金钱上的回报。

当兵很危险；贩毒或当妓女也很危险。显然，难点在于，从所有其它选择特定生活方式的动机中，将健康方面的风险和金钱上的回报区别开来。这并不容易，但经济学家正在进行尝试。

世界银行(World Bank)经济学家保罗•格特勒(Paul Gertler)和他的同事们估计，墨西哥妓女对其生命的估价为每年5万美元，其依据是她们愿意为了钱而不使用安全套。这个数目是其年收入的5倍，比例与富裕国家承受危险工作的工人相仿。

也有一些异常情况存在。《魔鬼经济学》(Freakonomics)作者史蒂文•莱维特(Steven Levitt)和社会学家素德赫•文卡特斯赫(Sudhir Venkatesh)计算，芝加哥的毒贩对其整个生命的估值介于5万美元至10万美元。事实上这很低，即便对于职业选择有风险偏好的贫穷年轻人来说也是如此。

不管这些计算存在何种缺陷，它们都是我们所拥有的最佳方法。这远非贬低生命的价值，此类研究往往突显出，我们的更安全、健康的现代生活，到底有多么珍贵。芝加哥大学商学院(Chicago Graduate School of Business)的凯文•墨菲(Kevin Murphy)最近访问了伦敦，展示他目前的研究，课题是美国1970年后医疗保健改善的价值。这一价值非常巨大，以目前的货币计算，大约为10万亿美元。回顾更久远的岁月，如果你必须在20世纪物质方面的进步，和医疗保健方面的改善中进行选择，这实在是难以取舍。医疗保健方面的收获，与其它所有进步的总和一样珍贵。令人鼓舞的是，在多数发展中国家，医疗保健改善的速度比富裕国家更快，表明全球不平等正在缩小。

对我自己来说，一个好消息是：墨菲计算，我采访他之前吃的那个美味奶酪汉堡包，只让我损失了价值1英镑的健康。这是笔很划算的交易。
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