The American labor market and middle class was once built on the routine job--workers showed up at factories and offices, took their places on the assembly line or the paper-pushing chain, did the same task over and over, and then went home.

New research from Henry Siu at the University of British Columbia and Nir Jaimovich from Duke University shows just how much the world of routine work has collapsed. The economists released a paper today, published by the centrist Democratic think tank Third Way, showing that over the...