'Honestly, when we first saw these patterns, we were so stunned we wondered if we made some mistake,' says Mr. Hungerman. 'We weren't even excited, we were like, 'Is that right?''

亨格曼说，老实说，当我们第一次发觉这种模式时，我们震惊不已，怀疑是不是弄错了。我们甚至一点都不兴奋，而是觉得，这样对吗？

He and Ms. Buckles estimate that family background accounts for up to 50% of the differences in education and earnings. That suggests to them that the compulsory-schooling effect Mr. Angrist and Mr. Krueger described could still be there, but that it can't be used to measure how schooling affects later earnings because it still mixes the effects of privilege and education instead of isolating them.

他和巴克尔斯估计，对于个人间教育程度和收入差异，家庭背景因素所占的比例最多为50%。他们认为，这表明安格瑞斯特和克鲁格所描述的义务教育法的影响可能仍然存在，不过不能用以衡量学校教育对后来的收入有何影响，因为家庭背景和学校教育的影响仍然混杂，而没有分开。