In some areas of social science, static analysis can be poison. Perhaps none moreso than the study of income distributions. Today's NY Times includes the latest update of a favored theme: "Cities Shed Middle Class, And Are Richer and Poorer For It."
The article lists the five metro areas with the smallest percentage of middle class families: New York, Los Angeles, McAllen, Baksersfield, Miami. Might these also be the ones with the largest immigrant populations? Is it safe to say that almost all of the immigrants (by definition) have moved up in the world? Especially in terms of their prospects?
Growing numbers (and proportions) of "high income" families mean that middle-income people are moving up. Growing numbers of "low income" families are largely explained by immigration.
Even the static analysis data shown can be seen in a positive light.