The relative importance of permanent (trend) versus cyclical shocks to GDP has been a central issue in macroeconomics, since the work of Nelson and Plosser (1982) and Morley et al. (2003) found large trend shocks. In contrast, Perron and Wada (2009) argued for a one time change in the mean...

The volatility of growth in U.S. real GDP declined dramatically in the mid-1980s. Viewed through the lens of linear autoregressive models, this phenomenon appears to be the result of a structural break in the innovation process that drives GDP fluctuations. We present an alternative model that...