Search results for "Multivariate statistics"
showing 10 items of 290 documents
Bodyweight, not age, determines oesophageal length and breaking strength in rats
2018
Delayed primary repair is still the method of choice in the management of long-gap oesophageal atresia in many centres, but the timing of anastomoses varies. Some assume the infant's bodyweight to be an important factor, whereas others prefer age. We therefore aimed to clarify whether age or bodyweight determined oesophageal length in a rodent model.We explanted the oesophagi of 20 Sprague-Dawley rats, aged 15 to 444 days (n = two per time point), measured bodyweight, oesophageal length, weight, and linear breaking strength to measure tissue resilience. Univariate and multivariate regression analyses were conducted to determine the influence of age and bodyweight on oesophageal length and l…
Associated factors with health-compromising behaviors among patients treated for oral cancer
2019
Background To improve eradication strategies of health-compromising behaviors between oral cancer survivors, this study aimed to explore the extent of clustering of risk behaviors and to assess possible factors associated. Material and Methods A cross-sectional study was carried out among oral cancer patients at least 6 months after treatment. They completed a questionnaire about smoking, alcohol consumption, oral hygiene habits and dental visits. Presence of clusters was evaluated through pairwise Pearson correlations and principal component analysis. Factors associated with each identified cluster were analyzed with multivariate models. Results Among 142 patients, 14.8% smoked, 51.7% cons…
Robust estimation of partial directed coherence by the vector optimal parameter search algorithm
2009
We propose a method for the accurate estimation of Partial Directed Coherence (PDC) from multichannel time series. The method is based on multivariate vector autoregressive (MVAR) model identification performed through the recently proposed Vector Optimal Parameter Search (VOPS) algorithm. Using Monte Carlo simulations generated by different MVAR models, the proposed VOPS algorithm is compared with the traditional Vector Least Squares (VLS) identification method. We show that the VOPS provides more accurate PDC estimates than the VLS (either overall and single-arc errors) in presence of interactions with long delays and missing terms, and for noisy multichannel time series. ©2009 IEEE.
Matrix Shuffle- Exchange Networks for Hard 2D Tasks
2021
Convolutional neural networks have become the main tools for processing two-dimensional data. They work well for images, yet convolutions have a limited receptive field that prevents its applications to more complex 2D tasks. We propose a new neural model, called Matrix Shuffle-Exchange network, that can efficiently exploit long-range dependencies in 2D data and has comparable speed to a convolutional neural network. It is derived from Neural Shuffle-Exchange network and has O(log N) layers and O(N ^ 2 log N) total time and O(N^2) space complexity for processing a NxN data matrix. We show that the Matrix Shuffle-Exchange network is well-suited for algorithmic and logical reasoning tasks on …
Spatial structure of helminth communities in the golden grey mullet, Liza aurata (Actinopterygii: Mugilidae), from the Western Mediterranean.
2012
Ecological investigations regarding the parasite fauna of grey mullets are scarce. The present study provides a detailed description of the helminth communities of Liza aurata in the Spanish western Mediterranean and analyzes the role of spatial, temporal, and host variables in shaping the infracommunities. In total, 204 fish were collected in 2 localities, situated ca. 290 km apart, in spring and fall of 2004 and 2005. A non-metric multidimensional scaling (NMDS) was used to visualize an ordination of the infracommunities according to their relative similarities in parasite abundances. The relationship between infracommunity composition and explanatory variables (host size, locality, year,…
Distribution of Brachionus species in Spanish mediterranean wetlands
1987
In this study 200 zooplankton samples were Burjassotcollected (1979–1980), from 57 different wetlands in coastal Mediterranean Spain (CMS) and examined for the occurrence of Brachionus species. Data on 17 separate physical and chemical features of these water bodies were obtained from samples collected at the same time. Ten different Brachionus species were found in these wetlands, but only six occurred frequently enough to allow further examination of their distributional patterns using multivariate discriminant analysis. To separate these species, three analyses were performed using the 17 physical and chemical parameters, or their ratios. Three discriminant functions accounted for 80% or…
Using topographical attributes to evaluate gully erosion proneness (susceptibility) in two mediterranean basins: advantages and limitations
2015
Empirical multivariate predictive models represent an important tool to estimate gully erosion susceptibility. Topography, lithology, climate, land use and vegetation cover are commonly used as input for these approaches. In this paper, two multivariate predictive models were generated for two gully erosion processes in San Giorgio basin (Italy) and Mula River basin (Spain) using only topographical attributes as independent variables. Initially, nine models (five for San Giorgio and four for Mula) with pixel sizes ranging from 2 to 50 m were generated, and validation statistics were calculated to estimate the optimal pixel size. The best models were selected based on model performance using…
THE ROLE OF SUNK COSTS IN THE DECISION TO INVEST IN R&D
2009
We present a dynamic empirical model of a firm's R&D decisions that is consistent with the existence of sunk R&D costs, taking into account that these costs may differ between small and large firms, and among different technological regimes. We estimate a multivariate dynamic discrete choice model using firm-level data of Spanish manufacturing for 1990–2000. Conditional on firm heterogeneity and serially correlated unobservable factors, we find that R&D history matters. This true state dependence allows inferring the existence of sunk R&D costs associated with performing R&D. Sunk R&D costs are found to be higher for large, high-tech firms.
Docking and multivariate methods to explore HIV-1 drug-resistance: a comparative analysis
2007
In this paper we describe a comparative analysis between multivariate and docking methods in the study of the drug resistance to the reverse transcriptase and the protease inhibitors. In our early papers we developed a simple but efficient method to evaluate the features of compounds that are less likely to trigger resistance or are effective against mutant HIV strains, using the multivariate statistical procedures PCA and DA. In the attempt to create a more solid background for the prediction of susceptibility or resistance, we carried out a comparative analysis between our previous multivariate approach and molecular docking study. The intent of this paper is not only to find further supp…
Study of the microstructure and efficiency of YSZ-SPS finely structured ceramic coatings
2018
Thanks to the using of liquid carrier, suspension plasma spray (SPS) enables the manufacture of finely structured coatings. As for conventional plasma spraying (APS), the microstructures of SPS coatings can be tailored by controlling the spray conditions. However, SPS is more complicated than APS due to its number of modifiable parameters.This thesis aims to provide a more fundamental understanding of the relationship between SPS process parameters and the properties of YSZ coatings by identifying generic models based on the use of mathematical statistical methods for the study of influence and sensitivity of the individual parameters.Systematic experiments were carried out to study the inf…