Janet Yellen worried about Stagnation

Some recent studies have raised the prospect that the economies of the United States and other countries will grow more slowly in the future as a result of both demographic factors and a slower pace of productivity gains from technological advances.

At an extreme, such developments could even amount to a type of "secular stagnation," in which monetary policy would need to keep real interest rates persistently quite low relative to historical norms to promote full employment and price stability, absent a highly expansive fiscal policy.