选择你感兴趣的两个国家——一个富一个穷。每一个国家的人均收入是多少?找一些可能有助于解释收入差别的国家特性的数据：投资率、人口增长率、受教育程度等等。(提示：世界银行的网站 www.wordbank.org 是找到这类数据的一个地点。)你将如何推断这些因素中哪些是造成观察到的收入差距的最重要的因素? Choose two countries that interest you——one rich and one poor. What is the income per person in each country? Find some data on country characteristics that might help explain the difference in income: investment rates, population growth rates, educational attainment, and so on. (Hint: The Web site of the World Bank, www.worldbank.org, is one place to find such data.) How might you figure out which of these factors is most responsible for the observed income difference?