Core Inflation: Robust Common Trend Model Forecasting

The monetary authorities need a future measure of in°ation trend to keep on tracking the in°ation on target. Many alternatives of the core in°ation measure have appeared in the recent literature pretending to avoid the de¯ciencies of the usual headline in°ation index as a predictor. This price index is de¯ned as some weighted average of the individual price change of a list of goods and services. To use it as the future in°ation indicator is criticized in the literature, as far as the products are heterogeneous in respect to the variability and some of the involved prices have relevant seasonal movements. A multivariate model including simultaneously the seasonal e®ects of each component of the price index and a common trend - the core in°ation - will be developed in this paper. The model will be phrased as a dynamic model and a robust sequential ¯lter will be introduced. The posterior and predictive distributions of the quantities of interest will be evaluated via stochastic simulation techniques, MCMC - Monte Carlo Markov Chain. Di®erent models will be compared using the minimum posterior predictive loss approach and many graphical illustrations will be presented.