Forecasting inflation through a bottom-up approach: How bottom is bottom?

The aim of this paper is to assess inflation forecast accuracy over the short-term horizon, using Consumer Price Index (CPI) disaggregated data, through a bottom-up approach. That is, aggregating forecasts is compared with aggregate forecasting. A new dimension to the question of to bottom-up or not is introduced by considering different levels of data disaggregation, namely a higher disaggregation level than the one considered up to now. This raises modelling issues that one has to cope with. In particular, it is suggested the use of a new strand of models, the Factor-Augmented SARIMA models. Considering as case-study the Portuguese one, we find an inverse relationship between the forecast horizon and the amount of information underlying the forecast, when minimizing the RMSFE.