Search results for "Multivariate statistics"
showing 10 items of 290 documents
Partial least squares X-ray fluorescence determination of trace elements in sediments from the estuary of Nerbioi-Ibaizabal River.
2010
The feasibility of partial least squares (PLS) regression modeling of X-ray fluorescence (XRF) spectra of estuarine sediments has been evaluated as a tool for rapid trace element content monitoring. Multivariate PLS calibration models were developed to predict the concentration of Al, As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, V and Zn in sediments collected from different locations across the estuary of the Nerbioi-Ibaizabal River (Metropolitan Bilbao, Bay of Biscay, Basque Country). The study was carried out on a set of 116 sediment samples, previously lyophilized and sieved with a particle size lower than 63 microm. Sample reference data were obtained by inductively coupled plasma mass …
Multivariate Frequency Domain Analysis of Causal Interactions in Physiological Time Series
2011
A common way of obtaining information about a physiological system is to measure one or more signals from the system, consider their temporal evolution in the form of numerical time series, and obtain quantitative indexes through the application of time series analysis techniques. While historical approaches to time series analysis were addressed to the study of single signals, recent advances have made it possible to study collectively the behavior of several signals measured simultaneously from the considered system. In fact, multivariate (MV) time series analysis is nowadays extensively used to characterize interdependencies among multiple signals collected from dynamical physiological s…
Accuracy of SCORTEN to predict the prognosis of Stevens‐Johnson syndrome/toxic epidermal necrolysis: a systematic review and meta‐analysis
2019
BACKGROUND The SCORTEN score is a specific predictor of the probability of death for patients diagnosed with Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN). OBJECTIVES To evaluate the overall accuracy of SCORTEN and the influence of several moderators such as age, sex, geographical region and age of the study. METHODS A systematic search was performed on MEDLINE, The Cochrane Library, EMBASE, SCOPUS and Web of Knowledge, with no restriction on language (last update 5 February 2019 for all databases). Original studies on the use of SCORTEN were eligible. The standardized mortality ratio (SMR), defined as the quotient between the number of deaths observed and the number expec…
253 PFS of elderly ovarian cancer patients might be predicted by G-8 geriatric screening tool – results of a retrospective cohort study
2021
Introduction/Background* The aim of this study was to evaluate the impact of the preoperative global health status on the prognosis of patients with ovarian cancer (OC) older than 60 years, who received cytoreductive surgery. Methodology G-8 geriatric screening tool (G-8 score), Lee Schonberg prognostic index, Eastern Cooperative Oncology Group (ECOG) performance status and Charlson Comorbidity Index (CCI) were determined retrospectively in a consecutive cohort of elderly patients with OC. Univariate and multivariate Cox regression analyses and Kaplan-Meier method were performed to analyze the impact of the preoperative global health status on survival. Result(s)* 116 patients entered the s…
The Relapsing Polychondritis Disease Activity Index: Development of a disease activity score for relapsing polychondritis.
2012
Abstract Objective The rarity of relapsing polychondritis (RP) has hindered the development of standardized tools for clinical assessment. Here, we describe the development of a preliminary score for disease assessing activity in RP, the Relapsing Polychondritis Disease Activity Index (RPDAI). Methods Twenty-seven RP experts participated in an international collaboration. Selection and definition of items for disease activity were established by consensus during a 4-round internet-based Delphi survey. Twenty-six experts assessed the Physician's Global Assessment (PGA) of disease activity on 43 test cases on a 0–100 scale, yielding a total of 1118 PGA ratings. The weight of each item was est…
Archetypal analysis: contributions for estimating boundary cases in multivariate accommodation problem
2013
[EN] The use of archetypal analysis is proposed in order to determine a set of representative cases that entail a certain percentage of the population, in the accommodation problem. A well-known anthropometric database has been used in order to compare our methodology with the common used PCA-approach, showing the advantages of our methodology: the level of accommodation is reached unlike the PCA approach, no more adjustments are necessary, the user can decide the number of archetypes to consider or leave the selection by a criterion. Unlike PCA, the objective of the archetypal analysis is obtaining extreme individuals, so it is the appropriate statistical technique for solving this type of…
Testing different methodologies for Granger causality estimation: A simulation study
2021
Granger causality (GC) is a method for determining whether and how two time series exert causal influences one over the other. As it is easy to implement through vector autoregressive (VAR) models and can be generalized to the multivariate case, GC has spread in many different areas of research such as neuroscience and network physiology. In its basic formulation, the computation of GC involves two different regressions, taking respectively into account the whole past history of the investigated multivariate time series (full model) and the past of all time series except the putatively causal time series (restricted model). However, the restricted model cannot be represented through a finit…
Vector Autoregressive Fractionally Integrated Models to Assess Multiscale Complexity in Cardiovascular and Respiratory Time Series
2020
Cardiovascular variability is the result of the activity of several physiological control mechanisms, which involve different variables and operate across multiple time scales encompassing short term dynamics and long range correlations. This study presents a new approach to assess the multiscale complexity of multivariate time series, based on linear parametric models incorporating autoregressive coefficients and fractional integration. The approach extends to the multivariate case recent works introducing a linear parametric representation of multiscale entropy, and is exploited to assess the complexity of cardiovascular and respiratory time series in healthy subjects studied during postu…
Elliptically Symmetric Distributions: A Review of Achieved Results and Open Issues
2005
The spherically and elliptically symmetrical distributions are used in different statistical areas for different purposes such as the description of multivariate data, in order to find alternatives to the normal distribution in multinormality tests and in the creation of statistical models in which the usual assumption of normality is not realistic. Some achieved results, open issues and some proposals for their use in applications, especially in the financial area, are here presented.
Asymmetric semi-volatility spillover effects in EMU stock markets
2018
Abstract The aim of this paper is to quantify the strength and the direction of semi-volatility spillovers between five EMU stock markets over the 2000–2016 period. We use upside and downside semi-volatilities as proxies for downside risk and upside opportunities. In this way, we aim to complement the literature, which has focused mainly on the contemporaneous correlation between positive and negative returns, with the evidence of asymmetry also in semi-volatility transmission. For this purpose, we apply the Diebold and Yilmaz (2012) methodology, based on a generalized forecast error variance decomposition, to downside and upside realized semi-volatility series. While the analysis of Diebol…