Outsourcing and Wages

From the Fed conference in Jackson Hole:

Two Princeton University economists claim that job outsourcing increased
productivity and real wages for low-skilled U.S. workers.
Princeton professors Gene Grossman and Esteban Rossi-Hansberg debated that salaries for the least-skilled blue collar jobs had been increasing since 1997 as outsourcing pushed productivity....The Princeton economists say that critics tended to gloss over the productivity benefits that come with offshoring labor.

I haven't read their paper, but here's the problem with this type of work: How do you link outsourcing to productivity increases for low wage workers? Productivity has increased in the US since 1997 and the US has outsourced, but it is difficult to show, causally, that outsourcing raises productivity. I'll have more on this after I read the paper.

Hat Tip: Mankiw's Blog