Journal articles
Fenga L, Galli M (In Press). Impact estimation on COVID-19 infections following school reopening in September 2020 in Italy. Journal of Statistics and Computer Science
Fenga L (In Press). Loss of Fitting and Distance Prediction in Fixed vs Updated ARIMA Models.
Global Journal of Science Frontier Research Volume XVII Issue. Year 2017Abstract:
Loss of Fitting and Distance Prediction in Fixed vs Updated ARIMA Models
In many cases, it might be advisable to keep an operational time series model fixed for a given span of time, instead of updating it as a new datum becomes available. One common case, is represented by model–based deseasonalization procedures, whose time series models are updated on a regular basis by National Statistical Offices. In fact, in order to minimize the extent of the revisions and grant a greater stability of the already released figures, the interval in between two updating processes is kept "reasonably" long (e.g. one year). Other cases can be found in many contexts, e.g. in engineering for structural reliability analysis or in all those cases where model re–estimation is not a practical or even a viable options, e.g. due to time constraints or computational issues. Clearly, the inevitable trade–off between a fixed models and its updated counterpart, e.g. in terms of fitting performances, out–of–sample prediction capabilities or dynamics explanation should be always accounted for.
Abstract.
Fenga L, Son-Turan S (2022). Forecasting youth unemployment in the aftermath of the COVID-19 pandemic: the Italian case. International Journal of Scientific and Management Research, 05(01), 75-91.
Fenga L, Del Castello C (2021). COVID-19: Metaheuristic Optimization-Based Forecast Method on Time-Dependent Bootstrapped Data.
Journal of Probability and Statistics,
2021, 1-7.
Abstract:
COVID-19: Metaheuristic Optimization-Based Forecast Method on Time-Dependent Bootstrapped Data
A compounded method—exploiting the searching capabilities of an operation research algorithm and the power of bootstrap techniques—is presented. The resulting algorithm has been successfully tested to predict the turning point reached by the epidemic curve followed by the COVID-19 virus in Italy. Future lines of research, which include the generalization of the method to a broad set of distribution, will be finally given.
Abstract.
Fenga L (2021). CoViD-19: an automatic, semiparametric estimation method for the population infected in Italy.
PeerJ,
9, e10819-e10819.
Abstract:
CoViD-19: an automatic, semiparametric estimation method for the population infected in Italy
To date, official data on the number of people infected with the SARS-CoV-2—responsible for the Covid-19—have been released by the Italian Government just on the basis of a non-representative sample of population which tested positive for the swab. However a reliable estimation of the number of infected, including asymptomatic people, turns out to be crucial in the preparation of operational schemes and to estimate the future number of people, who will require, to different extents, medical attentions. In order to overcome the current data shortcoming, this article proposes a bootstrap-driven, estimation procedure for the number of people infected with the SARS-CoV-2. This method is designed to be robust, automatic and suitable to generate estimations at regional level. Obtained results show that, while official data at March the 12th report 12.839 cases in Italy, people infected with the SARS-CoV-2 could be as high as 105.789.
Abstract.
Fenga L (2021). Forecasting the COVID-19 Diffusion in Italy and the Related Occupancy of Intensive Care Units. Journal of Probability and Statistics, 2021, 1-9.
Fenga L, Gaspari M (2021). Predictive Capacity of COVID-19 Test Positivity Rate.
Sensors,
21(7), 2435-2435.
Abstract:
Predictive Capacity of COVID-19 Test Positivity Rate
COVID-19 infections can spread silently, due to the simultaneous presence of significant numbers of both critical and asymptomatic to mild cases. While, for the former reliable data are available (in the form of number of hospitalization and/or beds in intensive care units), this is not the case of the latter. Hence, analytical tools designed to generate reliable forecast and future scenarios, should be implemented to help decision-makers to plan ahead (e.g. medical structures and equipment). Previous work of one of the authors shows that an alternative formulation of the Test Positivity Rate (TPR), i.e. the proportion of the number of persons tested positive in a given day, exhibits a strong correlation with the number of patients admitted in hospitals and intensive care units. In this paper, we investigate the lagged correlation structure between the newly defined TPR and the hospitalized people time series, exploiting a rigorous statistical model, the Seasonal Auto Regressive Moving Average (SARIMA). The rigorous analytical framework chosen, i.e. the stochastic processes theory, allowed for a reliable forecasting about 12 days ahead of those quantities. The proposed approach would also allow decision-makers to forecast the number of beds in hospitals and intensive care units needed 12 days ahead. The obtained results show that a standardized TPR index is a valuable metric to monitor the growth of the COVID-19 epidemic. The index can be computed on daily basis and it is probably one of the best forecasting tools available today for predicting hospital and intensive care units overload, being an optimal compromise between simplicity of calculation and accuracy.
Abstract.
Quattrociocchi L, Tibaldi M, Marsili M, Fenga L, Caputi M (2020). Active Ageing and Living Condition of Older Persons Across Italian Regions. Journal of Population Ageing, 14(1), 91-136.
Fenga L (2019). Filtering and prediction of noisy and unstable signals: the case of Google Trends data.
Journal of Forecasting,
39(2), 281-295.
Abstract:
Filtering and prediction of noisy and unstable signals: the case of Google Trends data
AbstractGoogle Trends data is a dataset increasingly employed for many statistical investigations. However, care should be placed in handling this tool, especially when applied for quantitative prediction purposes. Being by design Internet user dependent, estimators based on Google Trends data embody many sources of uncertainty and instability. They are related, for example, to technical (e.g. cross‐regional disparities in the degree of computer alphabetization, time dependency of Internet users), psychological (e.g. emotionally driven spikes and other form of data perturbations), linguistic (e.g. noise generated by double‐meaning words). Despite the stimulating literature available today on how to use Google Trends data as a forecasting tool, surprisingly, to the best of the author's knowledge, it appears that to date no articles specifically devoted to the prediction of these data have been published. In this paper, a novel forecasting method, based on a denoiser of the wavelet type employed in conjunction with a forecasting model of the class SARIMA (seasonal autoregressive integrated moving average), is presented. The wavelet filter is iteratively calibrated according to a bounded search algorithm, until a minimum of a suitable loss function is reached. Finally, empirical evidence is presented to support the validity of the proposed method.
Abstract.
Cerqueti R, Fenga L, Ventura M (2018). Does the U.S. exercise contagion on Italy? a theoretical model and empirical evidence. Physica A: Statistical Mechanics and its Applications, 499, 436-442.
Fenga L (2018). Smoothing parameter estimation for first order discrete time infinite impulse response filters. Biometrics & Biostatistics International Journal, 7(5).
Fenga L (2017). A wavelet threshold denoising procedure for multimodel predictions: an application to economic time series.
Statistical Analysis and Data Mining: the ASA Data Science Journal,
10(6), 410-421.
Abstract:
A wavelet threshold denoising procedure for multimodel predictions: an application to economic time series
Noise‐affected economic time series, realizations of stochastic processes exhibiting complex and possibly nonlinear dynamics, are dealt with. This is often the case of time series found in economics, which notoriously suffer from problems such as low signal‐to‐noise ratios, asymmetric cycles and multiregimes patterns. In such a framework, even sophisticated statistical models might generate suboptimal predictions, whose quality can further deteriorate unless time consuming updating or deeper model revision procedures are carried out on a regular basis. However, when the models' outcomes are expected to be disseminated in timeliness manner (as in the case of Central Banks or national statistical offices), their modification might not be a viable solution, due to time constraints. On the other hand, if the application of simpler linear models usually entails relatively easier tuning‐up procedures, this would come at the expenses of the quality of the predictions yielded. A mixed, self‐tuning forecasting method is therefore proposed. This is an automatic, 2‐stage procedure, able to generate predictions by exploiting the denoising capabilities provided by the wavelet theory in conjunction with a compounded forecasting generator. Its out‐of‐sample performances are evaluated through an empirical study carried out on macroeconomic time series.
Abstract.
Fenga L (2017). Bootstrap Order Determination for ARMA Models: a Comparison between Different Model Selection Criteria.
Journal of Probability and Statistics,
2017, 1-12.
Abstract:
Bootstrap Order Determination for ARMA Models: a Comparison between Different Model Selection Criteria
The present paper deals with the order selection of models of the class for autoregressive moving average. A novel method—previously designed to enhance the selection capabilities of the Akaike Information Criterion and successfully tested—is now extended to the other three popular selectors commonly used by both theoretical statisticians and practitioners. They are the final prediction error, the Bayesian information criterion, and the Hannan-Quinn information criterion which are employed in conjunction with a semiparametric bootstrap scheme of the type sieve.
Abstract.
Fenga L, Politis DN (2017). LASSO order selection for sparse autoregression: a bootstrap approach. Journal of Statistical Computation and Simulation, 87(14), 2668-2688.
Fenga L (2016). Time Series Chaos Detection and Assessment via Scale Dependent Lyapunov Exponent.
International Journal of Statistics and Probability,
5(6), 1-1.
Abstract:
Time Series Chaos Detection and Assessment via Scale Dependent Lyapunov Exponent
Many dynamical systems in a wide range of disciplines -- such as engineering, economy and biology -- exhibit complex behaviors generated by nonlinear components which might result in deterministic chaos. While in lab--controlled setups its detection and level estimation is in general a doable task, usually the same does not hold for many practical applications. This is because experimental conditions imply facts like low signal--to--noise ratios, small sample sizes and not--repeatability of the experiment, so that the performances of the tools commonly employed for chaos detection can be seriously affected. to tackle this problem, a combined approach based on wavelet and chaos theory is proposed. This is a procedure designed to provide the analyst with qualitative and quantitative information, hopefully conducive to a better understanding of the dynamical system the time series under investigation is generated from. The chaos detector considered is the well known Lyapunov Exponent. A real life application, using the Italian Electric Market price index, is employed to corroborate the validity of the proposed approach.
Abstract.
Fenga L, Politis DN (2013). Bootstrap order selection for SETAR models. Journal of Statistical Computation and Simulation, 85(2), 235-250.
Fenga L, Politis DN (2011). Bootstrap-based ARMA order selection. Journal of Statistical Computation and Simulation, 81(7), 799-814.
Battaglia F, Fenga L (2003). Forecasting Composite Indicators with Anticipated Information: an Application to the Industrial Production Index.
Journal of the Royal Statistical Society Series C: Applied Statistics,
52(3), 279-290.
Abstract:
Forecasting Composite Indicators with Anticipated Information: an Application to the Industrial Production Index
Summary
. Many economic and social phenomena are measured by composite indicators computed as weighted averages of a set of elementary time series. Often data are collected by means of large sample surveys, and processing takes a long time, whereas the values of some elementary component series may be available a considerable time before the others and may be used for forecasting the composite index. This problem is addressed within the framework of prediction theory for stochastic processes. A method is proposed for exploiting anticipated information to minimize the mean-square forecast error, and for selecting the most useful elementary series. An application to the Italian general industrial production index is illustrated, which demonstrates that knowledge of anticipated values of some, or even just one, component series may reduce the forecast error considerably.
Abstract.
Missori P, Fenga L, Maraglino C, Rocchi G, Nardacci B, Calderaro G, Salvati M, Delfini R (2000). Spontaneous Acute Subdural Hematomas. A Clinical Comparison with Traumatic Acute Subdural Hematomas. Acta Neurochirurgica, 142(6), 697-701.