Effects of the Hodrick-Prescott filter on trend and difference stationary time series Implications for business cycle research

When applied to persistent time series, the Hodrick-Prescott filter can generate business cycle dynamics even if none are present in the original data. Hence the presence of business cycles in HP filtered data does not imply that there are business cycles in the original data. For example, we show that standard real business cycle models do not generate business cycle dynamics in pre-filtered data and that the business cycles observed in HP filtered data are due to the filter. As another example, we show that under plausible assumptions HP stylized facts are determined primarily by the filter and reveal little about the dynamics of the underlying data.