The expansion has been long, and has attained a remarkably low level of unemployment without inflation. Yet increases in real wages have been disappointingly low, as have increases in measured productivity.
Expansions do end.
Structural changes over the past century have been immense, carrying us from a largely agricultural economy with poor communications, small firms, and relatively unproductive and rigid technologies to today's largely service economy with extraordinary access to information and giant firms. Yet the phenomenon of the business cycle persists, with at least qualitative continuity in its mechanisms and effects. Romer, however, does not argue that there have been no changes in the business cycle. The coming of automatic stabilizers and the rise of central banks have allowed monetary policy to offset many of the kinds of shocks that generated pre-Depression business cycles.