我们还能相信预测吗？

Full disclosure: for much of my professional life I have been an economic forecaster. So I felt targeted when Michael Gove, a leading Brexiter, said during the EU referendum campaign that “the people of this country have had enough of experts with organisations with acronyms saying that they know what is best and getting it consistently wrong”.

首先，我需要先全面披露一下我的身分：在我职业生涯的大部分时间里，我一直是一个经济预测者。因此，当英国退欧派的领军人物迈克尔•戈夫(Michael Gove，见上图)在退欧公投运动中说“这个国家的民众已经受够了那些来自名字为缩写的组织、声称他们知道什么是最好、但却不断搞错的专家”，我感觉自己成了靶子。

In a single blow, total denigration of experts, economic forecasting and forecasters. But surely there are some points to be placed on the other side of the ledger?

这是将专家、经济预测和预测者“一网打尽”的一击。但我们肯定还有一些砝码能放在天平的另一边吧?

First, it is a feature of the human condition that we are interested in what the future will bring. We rely on forecasts in daily life more than we might think. Before we leave home in the morning we listen to a weather forecast to decide what clothes to wear and a traffic forecast to decide what route to take to work. We make our own forecasts. By opting not to take a raincoat and taking the car, say, I am forecasting, albeit implicitly, that it will not rain and that the traffic will be manageable.

首先，人的一个特性就是会对未来会怎么样感兴趣。在日常生活中，我们比想象中还要依赖预测。早上离家之前，我们会听天气预报来决定穿什么衣服，听交通预测来决定走什么路线去上班。我们也会做出自己的预测。比如，我选择不带雨衣并且开车上班，那么尽管没有说出来，我预测今天不会下雨，交通情况也还能接受。

Furthermore, the reason that there are so many economic and financial forecasts is that people not only want them and need them, they also pay for them. The best economic forecasts tend to be the ones produced by organisations with the necessary computing power, and forecasting teams who provide the underlying data and spell out their assumptions. Users are thereby able to understand how the forecast was arrived at.

再者，有这么多经济和金融预测的原因，是人们不仅想要、需要这些预测，而且他们也为一些预测付费。最优的经济预测往往来自那些拥有必要的计算能力的组织，以及提供基础数据并详细阐明其假设的预测团队，这让用户能够理解预测是怎么来的。

What about accuracy? Almost all forecasts are “wrong” to some degree. A forecast that consumer price inflation will be 3 per cent in a year’s time can be judged to have been “wrong” if the final figure comes out at 3.1 per cent. But that does not make the forecast useless. What matters is whether the forecast materially helps, or misleads, the user.

准确度如何呢?几乎所有预测都在某种程度上是“错误”的。一项预测可能预言某年的消费者价格通胀将为3%，如果最终结果是3.1%，该预测也可能被判定为“错误”。这并不意味着预测是无用的。重要的是，预测在实质上是帮助还是误导了用户。

Weather forecasters have long appreciated this point. A farmer planning to spray his crop needs only to know whether it will rain, not how heavily. Similarly with economic and financial forecasts, the real issue is not one of arithmetic error; it is whether forecasts help or hinder the making of decisions. And here, inevitably, considerable responsibility rests with the user: it is unwise, irresponsible even, to use forecasts as a basis for making decisions they cannot support.

天气预报员一直非常认同这一观点。一个计划给庄稼浇水的农民只需要知道是否会下雨，并不必知道雨会下多大。经济和金融预测的情况也与此类似，真正的问题不是运算上的误差，而是预测对决策提供了帮助还是造成了阻碍。在这一点上，用户其实不可避免地要负相当一部分责任：一些预测并不足以作为决策的依据，如果非要根据这些预测进行决策，那就是不明智、甚至不负责任的。

Why discredit experts, then? In today’s “post-truth”, “post-fact” world, critics increasingly play the man rather than the ball. Where the economics profession is concerned, the tactic is as follows: first, make the principal test of their competence whether or not they can forecast accurately; then claim that they cannot do this; and finally conclude that there is no reason to take their analysis seriously.

那么，为何要贬低专家呢?在今天的“后真相”、“后事实”世界里，批评者日益对人不对事。针对干经济学这一行的，他们是这样做的：首先，对经济学家是否有能力准确预测进行检验;然后主张他们做不到这一点;最后得出结论，人们没有理由认真对待他们的分析。

John Van Reenen, a professor of applied economics at MIT, puts it thus: “[It is] as if the medical profession’s failure to predict the Aids epidemic means that you should ignore your doctor’s advice to give up smoking. No, we cannot predict the date you will die of lung cancer, but if you smoke we can be pretty sure your health will suffer.”

美国麻省理工学院(MIT)应用经济学教授约翰•范里宁(John van Reenen)因而有此一说：“这就好比因为医学界未能预测艾滋病会流行的缘故，就说明你应该无视医生让你戒烟的建议。是的，我们无法预测你会在哪一天死于肺癌，但如果你抽烟，我们很肯定你的健康将受损。”

And so to the final sleight of hand. Discrediting rational, fact-based analysis and those who use it to forecast, creates a vacuum; and with that comes the following, implicit, injunction: “Because these experts do not know what they are talking about, anyone’s view is equally valid.”

最后还有个花招。让人们怀疑基于事实的理性分析以及那些运用这些分析进行预测的人，从而制造出一种真空;同时传达一种含蓄的教导：“因为这些专家自己都不知所云，所以任何人的观点都同样有道理。”

This is a step too far. I am tempted to say to Mr Gove that when my wife developed cancer, we went to an expert — an oncologist. When I want to know tomorrow’s weather, I turn to a weather forecaster. And when I want to know what is most likely to happen to the economy, I turn to teams of professional forecasters who work for organisations with acronyms. The fact that they are unlikely to be exactly right does not give me any reason to suppose that Mr Gove will be.

这一步就有点过头了。我很想告诉戈夫，当我的妻子罹患癌症后，我们向一位专家——一位肿瘤医生求助。当我需要了解明天的天气时，我会查天气预报员播报的信息。当我想要了解经济态势时，我会向那些名字是缩写的组织旗下的专业预测团队求助。他们不太可能完全正确，但我不会据此认为戈夫的话是正确的。

The writer, partner in Llewellyn Consulting, was head of forecasting at the OECD and global chief economist at Lehman Brothers

本文作者是Llewellyn Consulting合伙人，曾任经合组织(OECD)预测主管、雷曼兄弟(Lehman Brothers)全球首席经济学家