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Covariance Models (covariance + models)
Selected AbstractsOn the modelling of over-ocean hurricane surface winds and their uncertaintyTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 642 2009Dr. S. P. Khare Abstract This paper investigates the modelling of over-ocean hurricane surface wind fields and their associated uncertainty. The wind models tested include parameterized balance models, a two-dimensional numerical planetary boundary-layer model and a three-dimensional (3D) linear analytical boundary-layer model. Using a set of archived over-ocean surface wind field reconstructions for validation, a series of cross-validation experiments has been performed for a range of norms. For norms that quantify predictability of vector fields, a particular configuration of the 3D analytical model was found to be superior to the other models tested. Using residual fields derived from fitting the wind models to the validation data, the issue of how to model the uncertainty (in the form of a covariance) in the speed field has also been examined. Covariance models based on truncated empirical orthogonal function representations were found to be optimal. Copyright © 2009 Royal Meteorological Society [source] A class of nonseparable and nonstationary spatial temporal covariance functionsENVIRONMETRICS, Issue 5 2008Montserrat Fuentes Abstract Spectral methods are powerful tools to study and model the dependency structure of spatial temporal processes. However, standard spectral approaches as well as geostatistical methods assume separability and stationarity of the covariance function; these can be very unrealistic assumptions in many settings. In this work, we introduce a general and flexible parametric class of spatial temporal covariance models, that allows for lack of stationarity and separability by using a spectral representation of the process. This new class of covariance models has a unique parameter that indicates the strength of the interaction between the spatial and temporal components; it has the separable covariance model as a particular case. We introduce an application with ambient ozone air pollution data provided by the U.S. Environmental Protection Agency (U.S. EPA). Copyright © 2007 John Wiley & Sons, Ltd. [source] Testing for separability of space,time covariancesENVIRONMETRICS, Issue 8 2005Matthew W. Mitchell Abstract Separable space,time covariance models are often used for modeling in environmental sciences because of their computational benefits. Unfortunately, there are few formal statistical tests for separability. We adapt a likelihood ratio test based on multivariate repeated measures to the spatio,temporal context. We apply this test to an environmental monitoring data set. Copyright © 2005 John Wiley & Sons, Ltd. [source] Plasma hemostatic factors and endothelial markers in four racial/ethnic groups: the MESA studyJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 12 2006P. L. LUTSEY Summary.,Background:,Hemostatic factors and endothelial markers may play some role in racial/ethnic differences in cardiovascular disease (CVD) rates. However, little information exists on hemostatic factors and endothelial markers across racial/ethnic groups. Objectives:,To describe, in four American racial/ethnic groups (Caucasian, Black, Hispanic, and Chinese), mean levels of selected hemostatic factors and endothelial markers. Patients and methods:,Multi-ethnic Study of Atherosclerosis baseline data were used (participant age: 45,84 years). Sex-specific analysis of covariance models, and t -tests for pairwise comparisons, were used to compare means of factors and markers. Adjustments were made for demographics and traditional CVD risk factors. Differences were significant at P < 0.05. Results:,Blacks had the highest levels of factor VIII, D-Dimer, plasmin,antiplasmin (PAP), and von Willebrand factor, among the highest levels of fibrinogen and E-selectin (women only), but among the lowest levels of intercellular adhesion molecule 1 (ICAM-1), and, in men, the lowest levels of plasminogen activator inhibitor-1 (PAI-1). Whites and Hispanics tended to have intermediate levels of factors and markers, although they had the highest levels of ICAM-1, and Hispanics had the highest mean levels of fibrinogen and E-selectin (women only). Chinese participants had among the highest levels of PAI-1, but the lowest, or among the lowest, of all other factors and markers. No soluble thrombomodulin differences were observed. Conclusions:,In this large cohort, hemostatic factor and endothelial marker mean levels varied by race/ethnicity, even after adjustment for traditional CVD risk factors. [source] Exercise and dietary change after diagnosis and cancer-related symptoms in long-term survivors of breast cancer: CALGB 79804PSYCHO-ONCOLOGY, Issue 2 2009Catherine M. Alfano Abstract Objective: Improving diet and exercise can reduce survivors' risk of cancer-related fatigue, poor physical functioning, and potential recurrence. A cancer diagnosis can represent a ,teachable moment', leading survivors to make positive changes in diet and exercise behaviors; however, little is known about how often this occurs or about factors that enhance or limit survivors' ability to make these changes. This cross-sectional descriptive study investigated both the prevalence and clustering of self-reported changes in diet and exercise and how these changes related to ongoing cancer-related symptoms, social support, and stressful life events among long-term breast cancer survivors. Methods: Survivors (n=227, response rate=72%) of a prior Cancer and Leukemia Group B treatment trial, on average 12 years post-diagnosis, completed a mailed survey assessing health behavior changes since diagnosis and current symptoms, social support, and stressful life events. Results: Over half of survivors reported making positive exercise or diet changes since diagnosis: over 25% reported making exercise and diet changes. Analyses of covariance models showed that survivors who reported increasing their exercise also reported lower fatigue. Trends were also found between increased fruit and vegetable intake and decreased fatigue and between increased exercise and increased social support. Conclusions: These results underscore the need for health promotion efforts among survivors. Exercise promotion is especially needed since more survivors attempted to change dietary behaviors than exercise on their own. Further, fatigue may limit survivors' ability to change their health behaviors; alternatively, survivors who increase their exercise may experience less fatigue. Copyright © 2008 John Wiley & Sons, Ltd. [source] Quetiapine for the treatment of bipolar mania in older adultsBIPOLAR DISORDERS, Issue 6 2008Martha Sajatovic Objectives:, A post hoc analysis of pooled data from two quetiapine monotherapy clinical trials was conducted to evaluate the efficacy and tolerability of quetiapine therapy (twice daily, 400,800 mg/day) among bipolar manic adults aged 55 years and older. The primary efficacy endpoint was the change from baseline in Young Mania Rating Scale (YMRS) total score at Day 21. A secondary endpoint was change from baseline in YMRS score at Day 84. Methods:, A total of 407 patients made up the safety population, consisting of 59 older adults (aged ,55 years) and 348 younger adults. A total of 403 patients made up the efficacy population, consisting of 59 older adults and 344 younger adults. Efficacy outcomes were analyzed using covariance models (ANCOVA); descriptive statistics are presented for safety outcomes. Results:, Both older and younger individuals treated with quetiapine had significant improvement from baseline on YMRS scores compared with placebo-treated patients. The older adult group demonstrated a sustained reduction in YMRS score compared with placebo that was apparent by Day 4 of treatment. For the quetiapine treatment groups, the most common adverse effects (at a frequency ,10%) were dry mouth, somnolence, postural hypotension, insomnia, weight gain, and dizziness in older adults, and dry mouth, somnolence, and insomnia in younger adults. For the placebo treatment groups, insomnia was the most common adverse event in both older and younger adults. Conclusions:, This secondary analysis suggests that quetiapine represents a potentially useful treatment option among older adults with bipolar I mania. Studies with a primary focus of geriatric bipolar mania, and including larger patient numbers, are needed to confirm these findings. [source] | ||||||||||