Frequently Asked Questions
  1. How does mobility in the U.S. compare to other countries?

    While we do not focus on comparisons across countries in our research, prior work [Corak 2013] has found that the U.S. has significantly lower levels of social mobility than most other developed countries. Our findings are consistent with these results. In the U.S., roughly 8% of children born to families in the bottom fifth of the income distribution reach the top fifth. Studying a similar time period and using analogous data, Boserup, Kopczuk, and Kreiner (2013) find that 11.7% of children in Denmark who start in the bottom fifth reach the top fifth, roughly twice the odds of "success" as in the U.S.


  2. What is Absolute Upward Mobility?

    Absolute Upward Mobility is a measure of the average economic outcome of a child from a below-median income family. Statistically, we define absolute upward mobility as the average percentile in the national income distribution of a child who is born to parents at the 25th percentile in the national income distribution. In areas with higher absolute upward mobility, children from low-income parents earn higher incomes on average as adults.


  3. What is Relative Mobility?

    Relative Mobility measures the difference in incomes between a child from a low income family vs. a high income family in a given area. Statistically, we define relative mobility as the average percentile in the national income distribution of a child who is born to the richest parents (top 1 percent of the national income distribution) minus the average percentile of a child born to poorest parents (bottom 1 percent). Smaller values of this statistic correspond to greater relative mobility, i.e. a smaller difference in outcomes between children from low vs. high income families.


  4. How do you define the Odds of Reaching Top Fifth Starting from Bottom Fifth?

    We start by taking the set of children whose parents are in the bottom 20% of the national income distribution. We then calculate the fraction of this group who reach the top 20% of the national income distribution in each area.


  5. What is a Commuting Zone?

    We divide the U.S. into 741 Commuting Zones. Commuting Zones are groups of counties that are defined based on commuting patterns. For example, if people in neighboring counties work in the same city, then those counties are likely to belong to the same Commuting Zone. Commuting zones are similar to metro areas, but have the advantage of covering rural areas as well. Note that each Commuting Zone is typically named after the biggest city in that zone. Hence, our statistics reflect average outcomes in a broad area around that city and not just that one city itself.


  6. Whom can I contact if I have questions about the study or the data?

    Please email us at This email address is being protected from spambots. You need JavaScript enabled to view it.