EXAMS 
 
Dear Economist,

My economics tutor says that I should be studying harder if I want to do well in my exams. I think that he is basing his advice on purely theoretical assumptions, and that there is no empirical evidence for his assertion. Who is right?

M.W., Cambridge

Dear M.W.,

You're probably correct that his advice is not based on empirical research – not because no research exists, but because it is very recent. But I am sorry to report that his wild speculations have now been confirmed by an intriguing natural experiment.

Previous researchers have struggled to establish a causal link between exam results and time spent studying. That is not a surprise. Bright students might work harder because theyenjoy the work. Or failing students might cram to rescue their grades. Untangling the statistics seems impossible.

Yet the puzzle has been resolved by Todd Stinebrickner, an economist, and his father, mathematician Ralph Stinebrickner. Equipped with detailed time-use questionnaires, they looked at students who were randomly assigned a room-mate with a games console. Neither the students nor their room-mates differed in, say, initial test score, time spent boozing, or sleeping. But students whose room-mates had video games spent less time studying and more playing Final Fantasy XII. Pure chance – the assignment of a room- mate – seems to affect time spent studying, and no other important decisions. And yes, the grades suffered.

If the analysis is correct, an extra hour a day studying has a very substantial impact on test scores – enough to lift a typical student into the top third. Unless you know some very good computer games, that is likely to be a rational investment of your time.

用功学习就一定考出好成绩？ 

亲爱的经济学家：

我的经济学导师说，如果我想在考试中取得好成绩，就应该更努力地学习。但我认为，他的建议完全建立在理论假设的基础上，而没有实证根据。谁是对的？

读者：M.W., 剑桥

亲爱的M.W.,

你说他的建议不是建立在实证研究基础上的，这种说法可能是对的：不是因为没有这方面的研究，而是因为这项研究最近才刚刚公布。我非常遗憾地告诉你，他的大胆揣测现在已经被一项有趣的自然试验证实了。

以前的研究人员难以在考试成绩和学习时间之间建立一种因果关系。这并不令人惊讶。好学生可能更用功，因为他们喜欢学习。差生可能为了几个而在考试前突击学习。解开这些统计数字似乎是不可能的。

但这个谜团被经济学家托德•斯坦布里克纳(Todd Stinebrickner)和他的父亲、数学家拉尔夫•斯坦布里克纳(Ralph Stinebrickner)解开了。他们给一些学生随机分配了一位拥有游戏机的室友，然后借助详细的时间使用问卷，对这些学生进行了考查。这些学生和他们的室友在初始测试成绩、喝酒或睡眠的时间等方面都没有差别。但那些室友有视频游戏机的学生减少了学习时间，将更多时间花在玩《最终幻想12》(Final Fantasy XII)上。纯粹的偶然——分配室友——似乎影响了学习的时间，不涉及其它任何重要决定。是的，这些学生的成绩受到了影响。

如果这项分析是正确的，那么每天多学习1小时就会对考试成绩有非常大的影响——足以将一名普通的学生提升到前三分之一。因此，多花点时间学习是一笔理性的投资，除非你知道一些非常好的电脑游戏。