Stevenson and Wolfers provide a number of possible reasons why this occurred, including non-comparable data over time, and increasing income inequality in the US during this period.

史蒂文森和沃尔弗斯给出了很多可能因素，解释造成此现象发生的原因，其中包括随着时间的消逝数据的不具可比性和这段时期内美国收入增加的日渐不平等。