Convergence in the United States

"We use non-parametric distribution dynamics techniques to reassess the convergence of per capita personal income (PCPI) across U.S. states and across metropolitan and nonmetropolitan portions of states for the period 1969-2005. The long-run distribution of PCPI is bimodal for both states and metro/nonmetro portions. Further- more, the high income mode of the distribution across metro and nonmetro portions corresponds to the single mode of the long-run distribution across metro portions only. These results (polarization or club-convergence) are reversed when weighting by population. The long run distributions across people are consistent with convergence. Migration and urbanization are the forces behind convergence"--Federal Reserve Bank of St. Louis web site.