The convergence of the economy's biggest mysteries

This past Friday brought news that the U.S. economy added 157,000 jobs in July, dropping unemployment to 3.9 percent. The unemployment rate has only gotten that low twice before in the last 50 years. Yet this spectacular performance has come with two bitter mysteries: Wage growth remains sluggish and productivity growth is pathetic. Economists aren't sure what to make of these twin puzzles: Some think there are two separate explanations; others that the productivity slowdown explains...