Recent studies suggest that this investment explains much of the increase in America's labour-productivity growth, to an average of almost 3% over the past five years, double the average in the previous 20 years.

ECONOMIST: Slowing down, to what? | The

It is more difficult to increase labour productivity in services than it is in manufacturing thus as real incomes rise we would expect the costs of services to rise relative to the costs of manufactures.

FORBES: America's Productivity Crisis