Does Real U.K. GDP Have a Unit Root? Evidence from a Multi-Century Perspective

Abstract

We employ the nonlinear unit-root test recently developed by Omay et al. (2018), as well as other linear and nonlinear tests, to examine the stationarity of five multi-century historical U.K. series of real output compiled by the Bank of England (Thomas and Dimsdale, 2017). Three series span 1270 to 2016 and two series span 1700 to 2016. These datasets represent the longest span of historical real output data available and, thus, provide the environment for which unit-root tests are most powerful. A key feature of the Omay et al. (2018) test is its simulataneous allowance for two types of nonlinearity: time-dependent (structural breaks) nonlinearity and state-dependent (asymmetric adjustment) nonlinearity. The key finding of the test, contrary to what other more popular nonlinear unit-root tests suggest, provides strong evidence that the main structure of the five series is a stationary process characterized by an asymmetric nonlinear adjustment and a permanent break affecting both the intercept and the trend. A major policy implication of this finding is fiscal and/or monetary stabilization policies have only temporary effects on the output levels of the United Kingdom.

Keywords: Unit Root, Time-Dependence, Nonlinearity, State-Dependence, Fourier Function

JEL Classification: C12, C22, O05