2010年10月18日星期一

曼昆还是很清醒的

所以他会在博客上推荐昨天纽时上谈论经济学哲学的文章(不是他本人所写)。他自己也 提醒大家模型和现实的区别。纽时这篇其实略有些乱。还是Russ Roberts半年前在WSJ上写得更透。大段摘录:

There were Nobel Laureates who thought the original stimulus package should have been twice as big. And there are those who blame it for keeping unemployment high. Some economists warn of hyperinflation while others tell us not to worry. It makes you wonder why people call it the Nobel Prize in Economic Science. After all, most sciences make progress. Nobody in medicine wants to bring back lead goblets. Sir Isaac Newton understood a lot about gravity. But Albert Einstein taught us more. But in economics, theories that were once discredited surge back into favor.

I once thought econometrics—the application of statistics to economic questions—would settle these disputes and the truth would out. Econometrics is often used to measure the independent impact of one variable holding the rest of the relevant factors constant. But I've come to believe there are too many factors we don't have data on, too many connections between the variables we don't understand and can't model or identify. I've started asking economists if they can name a study that applied sophisticated econometrics to a controversial policy issue where the study was so well done that one side's proponents had to admit they were wrong. I don't know of any.

Facts and evidence still matter. And economists have learned some things that have stood the test of time and that we almost all agree on—the general connection between the money supply and inflation, for example. But the arsenal of the modern econometrician is vastly overrated as a diviner of truth.

The defenders of modern macroeconomics argue that if we just study the economy long enough, we'll soon be able to model it accurately and design better policy. Soon. That reminds me of the permanent sign in the bar: Free Beer Tomorrow. We should face the evidence that we are no better today at predicting tomorrow than we were yesterday. Eighty years after the Great Depression we still argue about what caused it and why it ended. If economics is a science, it is more like biology than physics. Biologists try to understand the relationships in a complex system. That's hard enough. But they can't tell you what will happen with any precision to the population of a particular species of frog if rainfall goes up this year in a particular rain forest. They might not even be able to count the number of frogs right now with any exactness.

The bottom line is that we should expect less of economists. Economics is a powerful tool, a lens for organizing one's thinking about the complexity of the world around us. That should be enough. We should be honest about what we know, what we don't know and what we may never know. Admitting that publicly is the first step toward respectability.

最好通读全文。这篇评论,和下面这张图,都是对哈耶克这句话的极好诠释:The curious task of economics is to demonstrate to men how little they really know about what they imagine they can design.

点击看大图

1 条评论:

  1. I read an article written by Xiaokai Yang, saying that the current stage of economics is like alchemy in the development of chemistry.

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