AbstractThis paper discusses how the forecast accuracy of a Bayesian vector autoregression (BVAR) is affected by introducing the zero lower bound on the federal funds rate. As a benchmark I adopt a common BVAR specification, including 18 variables, estimated shrinkage, and no nonlinearity. Then I entertain alternative specifications of the zero lower bound. I account for the possibility that the effect of monetary policy on the economy is different in this regime, replace the federal funds rate by its shadow rate, consider a logarithmic transformation, feed in monetary policy shocks, or utilize conditional forecasts allowing for all shocks implemented through a rejection sampler. The latter two are also coupled with interest rate expectations from future contracts. It is shown that the predictive densities of all these specifications are greatly different, suggesting that this modeling choice is not innocuous. The comparison is based on the accuracy of point and density forecasts of major US macroeconomic series during the period 2009:1 to 2014:4. The introduction of the zero lower bound is not beneficial per se, but it depends on how it is done and which series is forecasted. With caution, I recommend the shadow rate specification and the rejection sampler combined with interest rate expectations to deal with the nonlinearity in the policy rate. Since the policy rate will remain low for some time, these findings could prove useful for practical forecasters.
Zero lower bound, unconventional monetary policy and indicator properties of interest rate spreads