Unit root tests of sigma income convergence across us metropolitan areas
用美国大陆所有都市区1969-2001年的人均收入和平均工资标准差数据，通过单位根检验发现收入差距并未缩小，支持收入发散观点。
The standard deviation of metropolitan per capita personal income (<it>PCPI</it>) and metropolitan average wage per job (<it>AWPJ</it>) provide straightforward indicators of unconditional sigma convergence for metropolitan economies within the United States. Using data for all metropolitan areas in the continental United States for the period 1969–2001, we tested for the unconditional sigma income convergence hypothesis by applying two unit root tests to the time series of the two standard deviations. Our results indicate that the time series can be described as random walks with drift, thereby supporting the claim that income divergence among metropolitan economies is not decreasing.