The second class of explanations focuses on the arguably improved performance of macroeconomic policies, particularly monetary policy. The historical pattern of changes in the volatilities of output growth and inflation gives some credence to the idea that better monetary policy may have been a major contributor to increased economic stability.
As Blanchard and Simon (2001) show, output volatility and inflation volatility have had a strong tendency to move together, both in the United States and other industrial countries. In particular, output volatility in the United States, at a high level in the immediate postwar era, declined significantly between 1955 and 1970, a period in which inflation volatility was low.