
NETS: Network estimation for time series
M. Barigozzi and C. Brownlees Journal of Applied Econometrics, 2019 

We model a large panel of time series as a VAR where the autoregressive matrices and the inverse covariance matrix of the system innovations are assumed to be sparse. The system has a network representation in terms of a directed graph representing predictive Granger relations and an undirected graph representing contemporaneous partial correlations. A lasso algorithm called NETS is introduced to estimate the model. We apply the methodology to analyse a panel of volatility measures of ninety bluechips. The model captures an important fraction of total variability, on top of what is explained by volatility factors, and improves outofsample forecasting. BACK 
Powerlaw partial correlation network models
M. Barigozzi, C. Brownlees, and G. Lugosi Electronic Journal of Statistics, 2018 

We introduce a class partial correlation network models whose network structure is determined by a random graph. I n particular in this work we focus on a version of the model in which the random graph has a powerlaw degree distribution. A number of crosssectional dependence properties of this class of models are derived. The main results we establish is that when the random graph is powerlaw, the system exhibits a high degree of collinearity. More precisely, the largest eigenvalues of the inverse covariance matrix converge to an affine function of the degrees of the most interconnected vertices in the network. The result implies that the largest eigenvalues of the inverse covariance matrix are approximately powerlaw distributed, and that, as the system dimension increases, the eigenvalues diverge. As an empirical illustration we analyse a panel of stock returns of a large set of companies listed in the S&P 500 and show that the covariance matrix of returns exhibits empirical features that are consistent with our powerlaw model. BACK 
Simultaneous multiple changepoint and factor analysis for highdimensional time series
M. Barigozzi, H. Cho, and P. Fryzlewicz Journal of Econometrics, 2018 

We propose the first comprehensive treatment of highdimensional time series factor models with multiple changepoints in their secondorder structure. We operate under the most flexible definition of piecewise stationarity, and estimate the number and loca tions of changepoints consistently as well as identifying whether they originate in the common or idiosyncratic components. Through the use of wavelets, we transform the problem of changepoint detection in the secondorder structure of a highdimensional time series, into the (relatively easier) problem of changepoint detection in the means of highdimensional panel data. Also, our methodology circumvents the difficult issue of the accurate estimation of the true number of factors in the presence of multiple changepoints by adopting a screening procedure. We further show that consistent factor analysis is achieved over each segment defined by the changepoints estimated by the proposed methodology. In extensive simulation studies, we observe that factor analysis prior to changepoint detection improves the detectability of changepoints, and identify and describe an interesting ‘spillover’ effect in which substantial breaks in the idiosyncratic components get, naturally enough, identified as changepoints in the common compo nents, which prompts us to regard the corresponding changepoints as also acting as a form of ‘factors’. Our methodology is implemented in the R package factorcpt, available from CRAN. BACK 
On the stability of euro area money demand and its implications for monetary policy
M. Barigozzi and A. Conti Oxford Bulletin of Economics and Statistics, 2018 

We employ a recent timevarying cointegration test to revisit the usefulness of longrun money demand equations for the ECB, addressing the issue of their instability by means of a model evaluation exercise. Building on the results, we make a twofold contribution. First, we propose a novel stable money demand equation relying on two crucial factors: a speculative motive, represented by domestic and foreign priceearnings ratios, and a precautionary motive, measured by changes in unemployment. Second, we use the model to derive relevant policy implications for the ECB, since excess liquidity looks more useful for forecasting stock market busts than future inflation. Overall, this evidence points to (i) a possible evolution of the monetary pillar in the direction of pursuing financial stability and (ii) the exclusion of a sudden liquidity–driven inflationary burst after the exit from the prolonged period of unconventional monetary measures. BACK 
Identification of global and local shocks in international financial markets via general dynamic factor models
M. Barigozzi, M. Hallin, and S. Soccorsi Journal of Financial Econometrics, 2018 

We employ a twostage general dynamic factor model to analyze comovements be tween returns and between volatilities of stocks from the US, European, and Japanese financial markets. We find two common shocks driving the dynamics of volatilities – one global shock and one USEuropean shock – and four local shocks driving returns, but no global one. Comovements in returns and volatilities increased considerably in the period 20072012 associated with the Great Financial Crisis and the European Sovereign Debt Crisis. We interpret this finding as the sign of a surge, during crises, of interdependencies across markets, as opposed to contagion. Finally, we introduce a new method for structural analysis in general dynamic factor models which is applied to the identification of volatility shocks via natural timing assumptions. The global shock has homogeneous dynamic effects within each individual market but more heterogeneous effects across them, and is useful for predicting aggregate realized volatilities. BACK 
Generalized dynamic factor models and volatilities: Estimation and forecasting
M. Barigozzi and M. Hallin Journal of Econometrics, 2017 

In large panels of financial time series with dynamic factor structure on the levels or returns, the volatilities of the common and idiosyncratic components often exhibit strong correlations, indicating that both are exposed to the same market volatility shocks. This suggests, alongside the dynamic factor decomposition of returns, a dynamic factor decomposition of volatilities or volatility proxies. Based on this observation, Barigozzi and Hallin (2015) proposed an entirely nonparametric and modelfree twostep general dynamic factor approach which accounts for a joint factor structure of returns and volatilities, and allows for extracting the market volatility shocks. Here, we go one step further, and show how the same twostep approach naturally produces volatility forecasts for the various stocks under study. In an applied exercise, we consider the panel of asset returns of the constituents of the S&P100 index over the period 20002009. Numerical results show that the predictors based on our twostep method outperform existing univariate and multivariate GARCH methods, as well as static factor GARCH models, in the pre diction of daily high–low range—while avoiding the usual problems associated with the curse of dimensionality. BACK 
A network analysis of the volatility of highdimensional financial series
M. Barigozzi and M. Hallin Journal of the Royal Statistical Society  series C, 2017 

Interconnectedness between stocks and firms plays a crucial role in the volatility contagion phenomena that characterise financial crises, and graphs are a natural tool in their analysis. In this paper, we are proposing graphical methods for an analysis of volatil ity interconnections in the Standard & Poor’s 100 dataset during the period 20002013, which contains the 20072008 Great Financial Crisis. The challenges are twofold: first, volatilities are not directly observed and have to be extracted from time series of stock returns; second, the observed series, with about 100 stocks, is highdimensional, and curse of dimensionality problems are to be faced. To overcome this double challenge, we pro pose a dynamic factor model methodology, decomposing the panel into a factordriven and an idiosyncratic component modelled as a sparse vector autoregressive model. The inversion of this autoregression, along with suitable identification constraints, produces networks in which, for a given horizon h, the weight associated with edge (i,j) represents the hstepahead forecast error variance of variable i accounted for by variable j’s innovations. Then, we show how those graphs yield an assessment of how systemic each firm is. They also demonstrate the prominent role of financial firms as sources of contagion during the 20072008 crisis. BACK 
Generalized dynamic factor models and volatilities: Recovering the market volatility shocks
M. Barigozzi and M. Hallin The Econometrics Journal, 2016 

Decomposing volatilities into a common marketdriven component and an idiosyncratic itemspecific one is an important issue in financial econometrics. This, however, requires the statistical analysis of large panels of time series, hence faces the usual challenges associated with highdimensional data. Factor model methods in such a context are an ideal tool, but they do not readily apply to the analysis of volatilities. Focusing on the reconstruction of the unobserved market shocks and the way they are loaded by the various items (stocks) in the panel, we propose an entirely nonparametric and modelfree twostep general dynamic factor approach to the problem, which avoids the usual curse of dimensionality. Applied to the S&P100 asset return dataset, the method provides evidence that a nonnegligible proportion of the marketdriven volatility of returns originates in the volatilities of the idiosyncratic components of returns. BACK 
Identifying the independent sources of consumption variation
M. Barigozzi and A. Moneta Journal of Applied Econometrics, 2016 

By representing a system of budget shares as an approximate factor model we determine its rank, i.e. the number of common functional forms, or factors and we estimate a base of the factor space by means of approximate principal components. We assume that the extracted factors span the same space of basic Engel curves representing the fundamental forces driving consumers' behaviour. We identify these curves by imposing statistical independence and by studying their dependence on total expenditure using local linear regressions. We prove consistency of the estimates. Using data from the U.K. Family Expenditure Survey from 1977 to 2006, we find strong evidence of two common factors and mixed evidence of a third factor. These are identified as decreasing, increasing, and almost constant Engel curves. The household consumption behaviour is therefore driven by two factors respectively related to necessities (e.g. food), luxuries (e.g. vehicles), and in some cases by a third factor related to goods to which is allocated the same percentage of total budget both by rich and poor households (e.g. housing). BACK 
Disentangling systematic and idiosyncratic dynamics in panels of volatility measures
M. Barigozzi, C. Brownlees, G. Gallo, and D. Veredas Journal of Econometrics, 2014 

Realized volatilities observed across several assets show a common secular trend and some idiosyncratic pattern which we accommodate by extending the class of Multiplicative Error Models (MEMs). In our model, the common trend is estimated nonparametrically, while the idiosyncratic dynamics are assumed to follow univariate MEMs. Estimation theory based on seminonparametric methods is developed for this class of models for large crosssections and large time dimensions. The methodology is illustrated using two panels of realized volatility measures between 2001 and 2008: the SPDR Sectoral Indices of the S&P500 and the constituents of the S&P100. Results show that the shape of the common volatility trend captures the overall level of risk in the market and that the idiosyncratic dynamics have a heterogeneous degree of persistence around the trend. Outofsample forecasting shows that the proposed methodology improves volatility prediction over several benchmark specifications. BACK 
Do euro area countries respond asymmetrically to the common monetary policy?
M. Barigozzi, A. Conti, and M. Luciani Oxford Bulletin of Economics and Statistics, 2014 

We investigate the possible existence of asymmetries among Euro Area countries reactions to the European Central Bank monetary policy. Our analysis is based on a Structural Dynamic Factor model estimated on a large panel of Euro Area quarterly variables. A lthough the introduction of the euro has changed the monetary transmission mechanism in the individual countries towards a more homogeneous response, we find that differences still remain between North and South Europe in terms of prices and unemployment. These results are the consequence of countryspecific structures, rather than of European Central Bank policies. BACK 
Nonfundamentalness in structural econometric models: A review
L. Alessi, M. Barigozzi, and M. Capasso International Statistical Review, 2011 

Current economic theory typically assumes that all the macroeconomic variables belonging to a given economy are driven by a small number of structural shocks. As recently argued, apart from negligible cases, the structural shocks can be recovered if the information set contains current and past values of a large, potentially infinite, set of macroeconomic variables. However, the usual practice of estimating small size causal Vector AutoRegressions can be extremely misleading as in many cases such models could fully recover the structural shocks only if future values of the few variables considered were observable. In other words, the structural shocks may be nonfundamental with respect to the small dimensional vector used in current macroeconomic practice. By reviewing a recent strand of econometric literature, we show that, as a solution, econometricians should enlarge the space of observations, and thus consider models able to handle very large panels of related time series. Among several alternatives, we review dynamic factor models together with their economic interpretation, and we show how nonfundamentalness is nongeneric in this framework. Finally, using a factor model, we provide new empirical evidence on the effect of technology shocks on labour productivity and hours worked. BACK 
Improved penalization for determining the number of factors in approximate factor models
L. Alessi, M. Barigozzi, and M. Capasso Statistics and Probability Letters, 2010 

The procedure proposed by Bai and Ng (2002) for identifying the number of factors in static factor models is revisited. In order to improve its performance, we introduce a tuning multiplicative constant in the penalty, an idea that was proposed by Hallin and Liška (2007) in the context of dynamic factor models. Simulations show that our method in general delivers more reliable estimates, in particular in the case of large idiosyncratic disturbances. BACK 