Cointegration versus Spurious Regression in Heterogeneous Panels

We consider the issue of cross sectional aggregation in nonstationary, heterogeneous panels where each unit cointegrates. We first derive the asymptotic properties of the aggregate estimate, and a necessary and sufficient condition for cointegration to hold in the aggregate relationship. We also develop an estimation and testing framework to verify whether the condition is met. Secondly, we analyze the case when cointegration doesn't carry through the aggregation process, investigating whether a mild violation can still lead to an aggregate estimator that summarizes the micro relationships reasonably well. We derive the asymptotic measure of the degree of non cointegration of the aggregated estimate and we provide estimation and testing procedures. A Monte Carlo exercise evaluates the small sample properties of the estimator.Aggregation, Cointegration, Heterogeneous Panel, Monte Carlo Simulation.

Testing for Breaks in Cointegrated Panels

We investigate the issue of testing for structural breaks in large cointegrated panels with common and idiosyncratic regressors. We prove a panel Functional Central Limit Theorem. We show that the estimated coefficients of the common regressors have a mixed normal distribution, whilst the estimated coefficients of the idiosyncratic regressors have a normal distribution. We consider strong dependence across the idiosyncratic regressors by allowing for the presence of (stationary and nonstationary) common factors. We show that tests based on transformations of Wald-type statistics have power versus alternatives of orde

Testing for Instability in Covariance Sturctures

We propose a test for the stability over time of the covariance matrix of multivariate time series. The analysis is extended to the eigensystem to ascertain changes due to instability in the eigenvalues and/or eigenvectors. Using strong Invariance Principle and Law of Large Numbers, we normalize the CUSUM-type statistics to calculate their supremum over the whole sample. The power properties of the test versus local alternatives and alternatives close to the beginning/end of sample are investigated theoretically and via simulation. The testing procedure is validated through an application to 18 US interest rates over 1997-2011, finding instability at the end-2007/beginning-2008

Testing for Breaks in Cointegrated Panels with Common and Idiosyncratic Stochastic Trends

In this paper, we develop tests for structural change in cointegrated panel regressions with common and idiosyncratic trends. We consider both the cases of observable and nonobservable common trends, deriving a Functional Central Limit Theorem for the partial sample estimators under the null of no break. We show that tests based on sup-Wald statistics are powerful versus breaks of size , also proving that power is present when the time of change differs across units and when only some units have a break. Our framework is extended to the case of cross correlated regressors and endogeneity. Monte Carlo evidence shows that the tests have the correct size and good power properties

THE PATIENT IN THE OPERATING ROOM: CONSIDERATION AT SEVEN YEARS FROM WORLD HEALTH ORGANIZATION GUIDELINES PUBLICATION.

Modern surgery is burdened by a huge amount of patient to be treated and an increasingly complex number of procedures which request planned action and shared behaviours, aimed to prevent perioperative accidents and favour good surgical outcomes. Surgical and anaesthetic safety has improved significantly in last few decades. However, the operating room environment continues to have significant safety risks for patients as well as the health care providers who work there. Adverse events may result from problems in practice, products, procedures or systems. The worldwide incidence of surgical site infection, one of the most important and frequent post-operative complication, ranges from 3% to 16%, with a mortality rate ranging from 0.4% to 0.8%; in these studies, about 50% of cases were considered preventable (1-9). Patients safety improvements demand a complex system-wide effort, involving a wide range of actions in performance improvement, environmental safety and risk management, including infection control, safe use of medicines, equipment safety, safe clinical practice and safe environment of care. Just as public health interventions and educational projects have dramatically improved maternal and neonatal survival, analogous efforts might improve surgical safety and quality of care (10). According to these objectives, the World Health Organization (WHO) has published and diffused the international “Guidelines for Safe Surgery” (11). The guidelines have the clear proposal to 61ameliorate the safety of surgical interventions; they define and promote recommendation and safety standards suitable for the different Countries and operative settings, suggesting a new deal in managing pre-operative, intra-operative and post-operative processes. On the base of these recommendations, the WHO has also developed a checklist for the safety in the operating room, in order to prevent avoidable adverse events, thus minimizing unnecessary loss of life and serious complications. The results raised from a multicentre study carried out in eight different Countries, demonstrating the effectiveness of the WHO checklist in terms of better patient safety, reduction of deaths and post-operative complications (12). The objectives of this international effort are resumable as follow: 1. the patient must be correctly positioned on the surgical bed and prepared; 2. the surgery team must operate on the correct patient at the correct site; 3. blood loss and risk for surgical site infection must be minimized; 4. inadvertent retention of instruments and sponges in surgical site must be prevented; 5. during surgery, anaesthesiologists must prevent harm from the administration of anaesthetics, while protecting the patient from pain; 6. anaesthesiologists must manage patient’s airways and respiratory function, in order to avoid life-threatening complications; 7. the team should consider patient’s allergies or intolerances in order to prevent an allergic or adverse drug reaction; 8. at the end of intervention, the surgical team must secure and accurately identify all surgical specimens, while the anaesthesiologists will guarantee a correct patient awakening; 9. all the members of the team will effectively communicate and exchange critical information for the safe conduct of the operation; 10. post-operative thromboembolism must be prevented adopting the right measures; 11. each member of the team is responsible for his own clinical documentation; 12. hospitals and public health systems will establish routine surveillance of surgical capacity, volume and results. On March 2013, the American Agency for Health Research and Quality (AHRQ) published the Making Health Care Safer II report, which confirmed the effectiveness of WHO checklist and considered it as one of the 10 strongest recommended practices health care organizations should immediately apply to improve patient safety (13). After the first launch of the WHO checklist, the American Veteran Health Administration observed a constant reduction of patient mortality (0.5/1000 surgeries/4 months); in Holland, compliance to the new guidelines raised from 12% of the first 4 months to the 60%, observed at the end of the second year after publication. This means that «The checklist only works if you use it» (14). The checklist does not reduces itself patient complications, but only the application of all the provided items could help to do so. The checklist should be understood not merely as a list of items to be checked off, but as an instrument for the improvement of communication, teamwork, and safety culture in the operating room, and it should be accordingly implemented. To reach the expected results it needs time, the time to let surgical team to learn and involve (gradually) all the interested units of a determined hospital or the hospitals of a specific geographic area. Agreeing with Bosk and colleagues (15), using an electronic recording format within the standard mandatory strategy facilitates apparent compliance and the use of the safety checklist as a tick box exercise. It seems that the main trick to improving safety is a strategy leading to positive attitudes on the part of the health professionals involved, involving a far more complex adaptive process than merely mandating the use of a checklist

The Asymptotics for Panel Models with Common Shocks

This paper develops a novel asymptotic theory for panel models with common shocks. We assume that contemporaneous correlation can be generated by both the presence of common regressors among units and weak spatial dependence among the error terms. Several characteristics of the panel are considered: cross sectional and time series dimensions can either be fixed or large; factors can either be observable or unobservable; the factor model can describe either cointegration relationship or a spurious regression, and we also consider the stationary case. We derive the rate of convergence and the distribution limits for the ordinary least squares (OLS) estimates of the model parameters under all the aforementioned cases

Modelling and Testing for Structural Changes in Panel Cointegration Models with Common and Idiosyncratic Stochastic Trend

In this paper, we propose an estimation and testing framework for parameter instability in cointegrated panel regressions with common and idiosyncratic trends. We develop tests for structural change for the slope parameters under the null hypothesis of no structural break against the alternative hypothesis of (at least) one common change point, which is possibly unknown. The limiting distributions of the proposed test statistics are derived. Monte Carlo simulations examine size and power of the proposed tests. We are grateful for discussions with Robert De Jong, Long-Fei Lee, Zongwu Cai, and Yupin Hu. We would also like to thank participants in the International Conferences on Common Features in London (Cass, 16-17 December 2004), 2006 New York Econometrics Camp and Breaks and Persistence in Econometrics (Cass, 11-12 December 2006), and econometrics seminars at Ohio State University and Academia Sinica for helpful comments. Part of this work was done while Chihwa Kao was visiting the Centre for Econometric Analysis at Cass (CEA@Cass). Financial support from City University 2005 Pump Priming Fund and CEA@Cass is gratefully acknowledged. Lorenzo Trapani acknowledges financial support from Cass Business School under the RAE Development Fund Scheme

Optimization of the energy for Breast monochromatic absorption X-ray Computed Tomography

The limits of mammography have led to an increasing interest on possible alternatives such as the breast Computed Tomography (bCT). The common goal of all X-ray imaging techniques is to achieve the optimal contrast resolution, measured through the Contrast to Noise Ratio (CNR), while minimizing the radiological risks, quantified by the dose. Both dose and CNR depend on the energy and the intensity of the X-rays employed for the specific imaging technique. Some attempts to determine an optimal energy for bCT have suggested the range 22keV\u201334keV, some others instead suggested the range 50keV\u201360keV depending on the parameters considered in the study. Recent experimental works, based on the use of monochromatic radiation and breast specimens, show that energies around 32keV give better image quality respect to setups based on higher energies. In this paper we report a systematic study aiming at defining the range of energies that maximizes the CNR at fixed dose in bCT. The study evaluates several compositions and diameters of the breast and includes various reconstruction algorithms as well as different dose levels. The results show that a good compromise between CNR and dose is obtained using energies around 28keV