In an important study, John Rogers (2003) of the Board staff analyzed annual data on the prices of 139 items, collected by the Economist Intelligence Unit for twenty-five European and thirteen U.S. cities. For his main results, Rogers divided the items into traded and non-traded categories, though he considered many other ways of slicing the data as well.
He then analyzed the cross-city dispersion of prices in each year. Of course, the reduction of barriers to trade, the harmonization of tax policies, and the increased efficiency of cross-national markets should lead to reduced dispersion in the prices of goods, especially actively traded goods, as competition and arbitrage reduce local monopoly power and differences in prices.