Focusing on the past few years, we see no consensus on how the mix of low- and high-wage jobs in the economy has evolved; estimates are extremely sensitive to the definition of job classes, the source of data, the time period, and method of calculation.
In any event, it is doubtful that changes in the pattern of wages in the U.S. economy can be explained by any single factor - trends in trade, in population and immigration, in unionization and labor market competition, in minimum wage policy, in the skill mix of the labor force, and in technology all play a role.