《经济学人》（The Economist）是一份创办于1843年的英国杂志，主要关注政治和商业方面的新闻。它是英语专业学生课外阅读的必备刊物，更是考研英语命题小组最钟爱的题源，历年考研真题中几乎有一半的文章都选自《经济学人》。

It's official: having friends of the opposite sex is bad for children's grade. Do friends of the opposite gender distract teenagers, hampering their academic performance? It may seem obvious, at least to paranoid parents, and yet it is hard to prove.

译文： 官方数据显示：与异性交朋友不利于孩子的学业成绩。与异性交朋友会使青少年分心，影响学业成绩？至少对多疑的家长而言这似乎显而易见，但证明起来很难。

Simple analysis of a survey of American schoolchildren conducted in 1995, for example, suggests no link between the proportion of a girl's friends who were boys and her grades. Boys with lots of female friends actually achieved better results than those with fewer.

译文： 比如，对1995年美国在校儿童一项调查的简单分析表明：女生的学业成绩与其异性朋友的比例无关。实际上，相较于异性朋友少的男生，异性朋友多的成绩更高。

A new paper by Andrew Hill of the University of South Carolina, however, digs deeper into the data, and comes to a different result. Friendship groups are not random, which makes it tricky to isolate the effect of fraternising with the opposite sex on school performance. Pushy parents, for instance, may both encourage after-school activities (hotbeds of hobnobbing across the gender divide) and help out with homework.

译文： 然而，南卡罗来纳大学的助理教授安德鲁·希尔发表的最新论文深入分析了这些数据，得出了不同的结论。朋友圈的非随机性使得单独考虑异性友谊对学业成绩的影响十分困难。例如，望子成龙的父母可能既鼓励课外活动（异性间亲密接触的温床）又赞同帮助解决家庭作业中的难题。

By the same token, the sort of boys who do not find it embarrassing to join a clique composed mainly of girls may also be more studious. Mr Hill gets around this by looking at the proportion of schoolmates of either sex living near each student. He reasons that parents do not choose where to live based on the sex of their neighbours' children.

译文： 同理，不会因加入以女生为主的小团体而感觉难为情的男孩也更加好学。为了解决上述问题，希尔将目光投向每位同学邻居中男女同学的比例。他推断父母不会以邻居家孩子的性别作为选择居所的标准。

The gender mix of near-neighbours should therefore be unrelated to the invisible factors that influence both friends and grades. But the mix of neighbours does influence friendship groups in school, since children are much more likely to befriend other children who live close by.

译文： 因此邻居家孩子的性别构成也应该与影响朋友和成绩的隐性因素无关。但是邻居间孩子的性别构成确实影响学校中朋友圈的形成，因为孩子们更倾向与住得近的孩子交朋友。

Mr Hill calculates the share of boys and girls among each child's 20 closest neighbours and uses this to identify random differences in friendship groups. He can then isolate the effect of having more friends of the opposite gender on school performance. He finds that for every 10% more children of the opposite sex among a student's friends, his or her grade-point average (GPA) declines by 0.1 (GPAs range from 0 to 4).

译文： 希尔先生计算了每个儿童20个最亲密的邻居中男女孩的比例并用上述计算结果确定了朋友圈的随机差异。他排除了学生交更多异性朋友对其学业成绩的影响。他发现一个学生的朋友中每多10%的异性朋友其各科平均绩点（GPA）会下降0.1(各科平均绩点从0~4)。

Below the age of 16, the effects are restricted to science and maths, but beyond 16 they spill over to English and history as well. Girls seem to be more prone to distraction, though Mr Hill cannot muster the statistical power to be certain. This tentative result is consistent with other studies that find that girls gain more from moving to single-sex schools.

译文： 这种影响在16岁以下仅限于科学和数学，但是在16岁以上会波及到英文和历史。尽管希尔先生没有搜集到确凿的统计数据，但是女孩子似乎更容易分心。这种不确定的结果与其他研究一致，这些研究都表明，转到女子学校上学的女孩子将学到更多。

Readers rushing to remove their children from co-ed schools should know, however, that Mr Hill's results came with a twist. Having more friends of the opposite sex may be bad for grades, but it has other effects, too.

译文： 然而，那些匆忙让自己孩子从男女同校转走的家长应当了解：希尔先生的结论有个意外发现。交更多的异性朋友可能不仅不利于学业成绩，还有其他影响。

Among the children from the original survey who were successfully re-interviewed 14 years later, those whose grades had been dragged down by friends of the opposite gender were more likely to be (or have been) married. Traditionalists worried about a child mooning over the heartthrob next door may comfort themselves with that.

译文： 在那些14年后顺利再次会面的参加初次调查的孩子中，因交异性朋友而成绩下降的孩子更可能（或已经）结婚。传统主义者担心痴想邻家梦中情人的孩子以此来安慰自己。