in no other u.s. recovery since world war ii have companies been simultaneously faster to boost spending on machines and software, while slower to add people to run them.

part of this is the old story of substituting capital for labor. but a combination of temporary tax breaks that allowed companies in 2011 to write off 100% of investments in the first year and historically low short- and long-term interest rates have pushed that process into overdrive.

hiring, meanwhile, is too slow to bring the unemployment rate down rapidly. employers have added workers at a monthly rate of 142,000 for ...