Modelli econometrici classici e multivariati

Auto-Regressive Distributed Lag was the standard model before the VAR model was invented. Compared to the VAR, it’s a less complex model, where the variables are not seen as interrelated. The main variable that are forecasted depends on the indicators, but the indicators do not depend on other indicators or the main variable.

I modelli di correzione degli errori vettoriali sono particolarmente utili per set di dati con relazioni a lungo termine (chiamate anche cointegrazione). I VECM sono tuttavia utili per stimare gli effetti a breve e lungo termine di una serie temporale su un'altra. Il termine correzione degli errori si riferisce al fatto che la deviazione dell'ultimo periodo da un equilibrio di lungo periodo, l'errore, ne influenza la dinamica a breve termine. Questi modelli stimano, oltre alle relazioni di lungo periodo tra le variabili, anche direttamente la velocità con cui una variabile dipendente ritorna all'equilibrio dopo una variazione di altre variabili.

The Minnesota BVAR is a Bayesian VAR model with a prior developed by Litterman and Sims at the University of Minnesota. Similar to how a penalized model shrinks the parameters towards zero, the Minnesota prior shrinks them towards a random walk. The prior also specifies a larger variance for shorter lags, implying a prior belief that shorter lags have a larger impact than longer.

The steady-state prior for a vector autoregressive (VAR) model makes it possible to incorporate prior information about the long-run average of economic time series. A classical example is inflation, which is expected to stabilize around a central bank’s target, typically 2% in the long run. The probabilistic nature of the steady-state prior allows the forecasters to control how strongly this prior knowledge influences the model. Steady-state priors have been shown to improve forecast accuracy at both short and long horizons across a wide range of macroeconomic forecasting applications. As a result, they are routinely usedby central banks and other policy institutions worldwide.

The convention of using a multiple time series model with constant parameters and assuming that the indicators in the model are hit with shocks of equal sizes over time may not always be realistic in practice, especially for longer periods of time. The Time-varying Bayesian VAR model can ease these assumptions and produce a more flexible model and is sometimes used in cases where the time period is a bit longer or when the economy is subject to policy changes.

Vector Auto Regression is a model that captures the linear relations among multiple time series. VAR models generalize the univariate autoregressive model (AR model) by allowing for multiple variables. All variables in a VAR enter the model in the same way: each variable has an equation explaining its evolution based on its own lagged values, the lagged values of the other model variables, and an error term. The calculations find the best common lag length for all variables in all equations (vectors).

In the statistical analysis of time series, Auto-Regressive–Moving-Average (ARMA) models provide a description of the relationships between the variables in terms of the two factors: autoregression (AR) and moving average (MA). The AR part involves regressing the variable on its own lagged (i.e. past) values. The MA part involves modeling the error term as a linear combination of error terms occurring contemporaneously and at various times in the past. VARMA is the VAR (multivariate) version of the ARMA model.