First, there is debate about the merits of the Detroit Free Press map purporting to show the extent of the decline in median household income in each state. See http://www.janegalt.net/archives/009439.html

Second, the study comparing the degree of income mobility in various developed nations requires context. Imagine that two poor Dutch families start with identical earnings. One stayed in Holland; the other moved to the US for three generations, and then returned. They each saw their income improve according to the average rate of income improvement in their respective countries. After three generations, which family would have the higher income?

The study doesn’t actually provide enough information to answer that question.

1. The study focuses on change in income across generations, not whether that change is up or down. Thus, if all nations had an equal propensity to see the children of the poor grow rich, but the US had a lower propensity to see the children of the rich grow poor, then the US would be deemed to have “lower mobility.” Would that be such a bad thing?

2. Do we value seeing the standard of living of poor families improve to the greatest extent, or do we value improvement as a percentage of average earnings? I understand the study to measure the latter, not the former. In other words, even if the standard of living of American poor families were improving faster than the standard of living of any other nation’s poor families, the US might seem to have “low mobility” because the standard of living of its rich families was growing even faster.

Note also that the study focuses on deviations from AVERAGE income, not from MEDIAN income, meaning that the results may be influenced by changes in both extreme wealth and extreme poverty. The extreme wealth of the US skews results that reflect average income.

None of this demonstrates that US poor families ARE better off than European ones; I merely note that the study doesn’t demonstrate the converse.