America's most prestigious universities have just gained a new argument to justify skyrocketing tuitions, thanks to research from one of their own professors.

美国最富盛名的大学刚刚获得了一个证明不断飙升的学费合理的新理由，这要得益于一名他们自己教授的研究结果。

In a new paper, Caroline Hoxby, a Stanford (and formerly Harvard) economist who specializes in educational issues, tackles a question dogging many parents of college-age children: Why it seems so much harder for their offspring to get into a good college than it was for them. A big part of the answer, she concludes, is that the market for education has gone global. That means the pool of applicants to the best universities has expanded to include students from many different backgrounds and locales--students who might once have aspired mainly to local schools.

斯坦福大学(Stanford)经济学家卡罗琳•霍克斯比(Caroline Hoxby)在一篇新论文中探讨了令很多大学生家长感到困惑的一个问题：为什么和他们当年相比，现在孩子上一所好大学会困难得多？霍克斯比曾在哈佛大学执教，教育问题是她的研究方向。霍克斯比认为，很大一部分原因是，教育市场正走向全球化。这意味着申请最优秀大学的生源范围扩大，如今包括了很多不同背景和地区的学生，而这些学生可能之前基本都想着上当地学校。

The phenomenon, she notes, has boosted selectivity only at the top institutions. In 2007, the average student accepted by the most selective 5% of colleges scored in the 98th percentile on entrance exams, compared to an average score in the 90th percentile in 1962. Meanwhile, as more students have set their sights higher, other colleges have become less selective. In fact, getting accepted at any college has actually become easier, Hoxby argues, as the total number of freshman seats has grown faster than the number of prepared high-school graduates.

霍克斯比说，这一现象只令上顶尖大学变得更困难。2007年，美国最顶级的5%大学的录取新生的平均入学考试成绩是排在所有考生的前2%，而1962年这一平均成绩是排在所有考生的前10%。与此同时，随着更多的学生眼光提高，其他学校挑选生源的选择余地下降。霍克斯比说，现在学生要被大学录取已经变得更加容易，因为大学的招生计划总数的增长速度要快于有志于读大学的高中毕业生数量。