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Mixed Effects (mixed + effects)
Terms modified by Mixed Effects Selected AbstractsSIMULATED MAXIMUM LIKELIHOOD APPLIED TO NON-GAUSSIAN AND NONLINEAR MIXED EFFECTS AND STATE,SPACE MODELSAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 4 2004Russell B. Millar Summary The paper presents an overview of maximum likelihood estimation using simulated likelihood, including the use of antithetic variables and evaluation of the simulation error of the resulting estimates. It gives a general purpose implementation of simulated maximum likelihood and uses it to re-visit four models that have previously appeared in the published literature: a state,space model for count data; a nested random effects model for binomial data; a nonlinear growth model with crossed random effects; and a crossed random effects model for binary salamander-mating data. In the case of the last three examples, this appears to be the first time that maximum likelihood fits of these models have been presented. [source] Global statistical analysis of MISR aerosol data: a massive data product from NASA's Terra satelliteENVIRONMETRICS, Issue 7 2007Tao Shi Abstract In climate models, aerosol forcing is the major source of uncertainty in climate forcing, over the industrial period. To reduce this uncertainty, instruments on satellites have been put in place to collect global data. However, missing and noisy observations impose considerable difficulties for scientists researching the global distribution of aerosols, aerosol transportation, and comparisons between satellite observations and global-climate-model outputs. In this paper, we fit a Spatial Mixed Effects (SME) statistical model to predict the missing values, denoise the observed values, and quantify the spatial-prediction uncertainties. The computations associated with the SME model are linear scalable to the number of data points, which makes it feasible to process massive global satellite data. We apply the methodology, which is called Fixed Rank Kriging (FRK), to the level-3 Aerosol Optical Depth (AOD) dataset collected by NASA's Multi-angle Imaging SpectroRadiometer (MISR) instrument flying on the Terra satellite. Overall, our results were superior to those from non-statistical methods and, importantly, FRK has an uncertainty measure associated with it that can be used for comparisons over different regions or at different time points. Copyright © 2007 John Wiley & Sons, Ltd. [source] Rust severity in bioenergy willow plantations treated with additional nutrientsFOREST PATHOLOGY, Issue 1 2009M. Toome Summary A 3-year field study was carried out to determine the effect of wastewater irrigation and previous differences in mineral fertilization on the occurrence of willow leaf rust (Melampsora epitea). The experiment was conducted in two energy forest plantations: one designed for wastewater purification and the other as a mineral fertilization experiment. The severity of leaf rust on different clones and sites with different treatments was assessed by counting the number of uredinia per leaf unit area. Generally, plants irrigated with wastewater consistently had more leaf rust, irrespective of the study years or willow clones. Previous mineral fertilization had mixed effects on different clones 2 years after the last application. Three years after the last fertilizer application, however, no impact of the treatment on rust disease development was detected. In general, the rust levels differed from year to year probably due to climate. In this study, no correlation was detected between shoot age and rust severity, whereas climate and treatments strongly influenced leaf rust levels on some willow clones. [source] The potential roles of biological soil crusts in dryland hydrologic cyclesHYDROLOGICAL PROCESSES, Issue 15 2006Jayne Belnap Abstract Biological soil crusts (BSCs) are the dominant living cover in many drylands of the world. They possess many features that can influence different aspects of local hydrologic cycles, including soil porosity, absorptivity, roughness, aggregate stability, texture, pore formation, and water retention. The influence of biological soil crusts on these factors depends on their internal and external structure, which varies with climate, soil, and disturbance history. This paper presents the different types of biological soil crusts, discusses how crust type likely influences various aspects of the hydrologic cycle, and reviews what is known and not known about the influence of biological crusts on sediment production and water infiltration versus runoff in various drylands around the world. Most studies examining the effect of biological soil crusts on local hydrology are done by comparing undisturbed sites with those recently disturbed by the researchers. Unfortunately, this greatly complicates interpretation of the results. Applied disturbances alter many soil features such as soil texture, roughness, aggregate stability, physical crusting, porosity, and bulk density in ways that would not necessarily be the same if crusts were not naturally present. Combined, these studies show little agreement on how biological crusts affect water infiltration or runoff. However, when studies are separated by biological crust type and utilize naturally occurring differences among these types, results indicate that biological crusts in hyperarid regions reduce infiltration and increase runoff, have mixed effects in arid regions, and increase infiltration and reduce runoff in semiarid cool and cold drylands. However, more studies are needed before broad generalizations can be made on how biological crusts affect infiltration and runoff. We especially need studies that control for sub-surface soil features such as bulk density, micro- and macropores, and biological crust structure. Unlike the mixed effects of biological crusts on infiltration and runoff among regions, almost all studies show that biological crusts reduce sediment production, regardless of crust or dryland type.Copyright © 2006 John Wiley & Sons, Ltd. [source] Trade and agroindustrialization in developing countries: trends and policy impactsAGRICULTURAL ECONOMICS, Issue 3 2000Eugenio Díaz-Bonilla Abstract There have been important changes in the international trade of processed and high-value added food products from developing countries over the past several decades. One of them has been the emergence of oilseeds and fruits and vegetables, replacing traditional products such as sugar, coffee, and cocoa as the main exports from developing countries. Another trend has been the collapse of African agroindustrial exports and the increase of exports from Asia. The paper highlights key trends, and explores possible reasons for the trends, focusing on trade policies in less-developed countries (LDCs) and developed countries (DCs). The paper argues that national trade policies and other economic policies appear to have been relatively supportive of agroindustrial production and exports in Asia. In contrast, policies have had more mixed effects in Latin America and the Caribbean (LAC), and seem to have been just one component in a larger array of forces inhibiting economic development in Africa. The performance of agroindustrial production and exports from LDCs may be now more dependent than ever on the completion of reforms in the agricultural trade policies of DCs. For Africa, however, a more supportive international environment and better macroeconomic and trade policies will not be enough to ensure a thriving agroindustrial sector within a broader process of economic development until military confrontations stop. [source] Regulation of Eukaryotic Initiation Factor 4E Phosphorylation in the Nervous System of Aplysia californicaJOURNAL OF NEUROCHEMISTRY, Issue 2 2000John R Dyer We have used an antibody that specifically recognizes eukaryotic initiation factor 4E (eIF4E) when it is phosphorylated at Ser207 to characterize eIF4E phosphorylation in the nervous system of Aplysia. The level of phosphorylated eIF4E, but not the level of total eIF4E, was significantly correlated with the basal rate of translation measured from different animals. Serotonin (5-HT), a transmitter that regulates the rate of translation in Aplysia neurons, had mixed effects on eIF4E phosphorylation. 5-HT decreased eIF4E phosphorylation in sensory cell clusters through activation of protein kinase C. 5-HT increased eIF4E phosphorylation in the whole pleural ganglia. In the Aplysia nervous system, eIF4E phosphorylation correlated with phosphorylation of the p38 MAP kinase, but not the p42 MAP kinase (ERK). Furthermore, an inhibitor of the p38 MAP kinase significantly decreased basal eIF4E phosphorylation, but an inhibitor of the MAP or ERK kinase (MEK) did not. Despite the correlation of eIF4E phosphorylation with the basal rate of translation, inhibition of eIF4E phosphorylation by an inhibitor of the p38 MAP kinase did not significantly decrease the rate of translation. [source] Serum 6-Beta-Naltrexol Levels Are Related to Alcohol Responses in Heavy DrinkersALCOHOLISM, Issue 9 2000Mary E. McCaul Background: There is strong evidence for the role of the endogenous opioid system in alcohol reinforcement and consumption; however, recent human laboratory studies and clinical trials have reported mixed effects of naltrexone (a nonselective opioid antagonist) on alcohol-related behaviors. This paper reports a secondary data analysis of a human laboratory study that examines the relationship between serum levels of 6-beta-naltrexol, the major, biologically active metabolite of naltrexone, and subjective effects of alcohol. Methods: The study used a within-subjects design to examine the effects of naltrexone (0, 50, and 100 mg/day) on subjective responses to alcohol (none, moderate, and high dose) in heavy drinkers (n= 23). Each subject received three doses of naltrexone in random order; each naltrexone dose was administered over an 8 day period on an inpatient unit, with a 1 week outpatient washout between doses. After stabilization at each of the naltrexone doses, subjects participated in three alcohol challenge sessions (none, moderate, and high dose) in random order; thus, each subject participated in a total of nine alcohol administration sessions. Results: Doubling the naltrexone dose (50 vs. 100 mg/day) doubled the mean serum 6-beta-naltrexol levels. At each naltrexone dose, there was a 4-fold range in 6-beta-naltrexol levels across subjects. Before alcohol administration, higher 6-beta-naltrexol levels were associated with higher ratings of sedation. After high-dose alcohol administration, higher 6-beta-naltrexol levels were associated with significantly lower ratings of liking and best effects. Conclusions: These findings provide further evidence of the involvement of the opioid system in the modulation of alcohol effects and suggest that serum 6-beta-naltrexol concentrations may be important in predicting therapeutic response to naltrexone. [source] Competitive displacement or biotic resistance?JOURNAL OF VEGETATION SCIENCE, Issue 2 2010Disentangling relationships between community diversity, invasion success of tall herbs, shrubs Abstract Questions: Are negative invasion,diversity relationships due to biotic resistance of the invaded plant community or to post-invasion displacement of less competitive species? Do invasion,diversity relationships change with habitat type or resident traits? Location/species: Lowlands and uplands of western and southern Germany, Heracleum mantegazzianum; mountain range in central Germany, Lupinus polyphyllus; and coastal dunes of northwest Germany, Rosa rugosa. Methods: We tested the significance and estimated regression slopes of invasion,diversity relationships using generalized linear (mixed effects) models relating invader cover and habitat type to species richness in different plant groups, stratified based on size, life cycle and community association. Results: We found negative, positive and neutral relationships between invader cover and species richness. There were negative linear correlations of invader cover with small plant species throughout, but no negative linear correlation with tall species. Invasion,diversity relationships tended to be more negative in early-successional habitats, such as dunes or abandoned grasslands, than in late-successional habitats. Conclusions: Invasion diversity,relationships are complex; they vary among habitat types and among different groups of resident species. Negative invasion,diversity relationships are due to asymmetric competitive displacement of inferior species and not due to biotic resistance. Small species are displaced in early-successional habitats, while there is little effect on persistence of tall species. [source] The Indian Movement and Political Democracy in EcuadorLATIN AMERICAN POLITICS AND SOCIETY, Issue 3 2007Leon Zamosc ABSTRACT This article examines the implications of the Ecuadorian Indian movement for democratic politics. During the 1990s, the movement successfully fostered indigenous and popular participation in public life, influenced government policies, and became a contender in power struggles. But in the institutional domain, the participatory breakthrough had mixed effects. While the movement fulfilled functions of interest representation and control of state power, its involvement in a coup attempt demonstrated that its political socialization had not nurtured a sense of commitment to democracy. The evidence is discussed by reference to the proposition that civil society actors may or may not contribute to democracy. The article argues that the study of the democratic spinoffs of civil activism requires a context-specific approach that considers the particularistic orientations of civil associations and pays attention to their definition of means and ends, the institutional responses evoked by their initiatives, and the unintended consequences of their actions. [source] A unified approach to estimation of nonlinear mixed effects and Berkson measurement error modelsTHE CANADIAN JOURNAL OF STATISTICS, Issue 2 2007Liqun Wang Abstract Mixed effects models and Berkson measurement error models are widely used. They share features which the author uses to develop a unified estimation framework. He deals with models in which the random effects (or measurement errors) have a general parametric distribution, whereas the random regression coefficients (or unobserved predictor variables) and error terms have nonparametric distributions. He proposes a second-order least squares estimator and a simulation-based estimator based on the first two moments of the conditional response variable given the observed covariates. He shows that both estimators are consistent and asymptotically normally distributed under fairly general conditions. The author also reports Monte Carlo simulation studies showing that the proposed estimators perform satisfactorily for relatively small sample sizes. Compared to the likelihood approach, the proposed methods are computationally feasible and do not rely on the normality assumption for random effects or other variables in the model. Une stratégie d'estimation commune pour les modèles non linéaires à effets mixtes et les modèles d'erreur de mesure de Berkson Les modèles à effets mixtes et les modèles d'erreur de mesure de Berkson sont très usités. Ils par-tagent certaines caractéristiques que l'auteur met à profit pour élaborer une stratégie d'estimation commune. II considère des modèles dans lesquels la loi des effets aléatoires (ou des erreurs de mesure) est paramé-trique tandis que celles des coefficients de régression aléatoires (ou de variables exogènes non observées) et des termes d'erreur ne le sont pas. II propose une estimation des moindres carrés au second ordre et une approche par simulation fondées sur les deux premiers moments conditionnels de la variable endogène, sachant les variables exogènes observées. Les deux estimateurs s'avèrent convergents et asymptotiquement gaussiens sous des conditions assez générales. L'auteur fait aussi état d'études de Monte-Carlo attestant du bon comportement des deux estimations dans des échantillons relativement petits. Les méthodes proposées ne posent aucune difficulté particulière au plan numérique et au contraire de l'approche par vraisemblance, ne supposent ni la normalité des effets aléatoires, ni celle des autres variables du modèle. [source] THE GLOBAL BANK MERGER WAVE: IMPLICATIONS FOR DEVELOPING COUNTRIESTHE DEVELOPING ECONOMIES, Issue 4 2002GARY A. DYMSKI This paper reconsiders causes and implications of the global bank merger wave, especially for developing economies. Previous studies of the global bank mergers,that is, mergers between banks from different nations,had assumed that these combinations are efficiency-driven, and that the U.S. case defines the paradigm for all other nations' banking systems. This paper argues that the U.S. experience is unique, not paradigmatic, and that bank mergers are not efficiency-driven; instead, this merger wave has arisen because of macrostructural circumstances and because of shifts over time in banks' strategic motives. This paper argues that large, offshore banks often engage in cross-border mergers because they want to provide financial services to households and firms that have reached minimal threshold wealth levels. For developing economies, this suggests that cross-border acquisitions of local banks by offshore banks will have mixed effects; and it cannot be assumed that the net social impact is positive. [source] Evidence-Based Strategies for Reducing Cesarean Section Rates: A Meta-AnalysisBIRTH, Issue 1 2007Nils Chaillet PhD ABSTRACT: Background: Canada's cesarean section rate reached an all-time high of 22.5 percent of in-hospital deliveries in 2002 and was associated with potential maternal and neonatal complications. Clinical practice guidelines represent an appropriate mean for reducing cesarean section rates. The challenge now lies in implementing these guidelines. Objectives of this meta-analysis were to assess the effectiveness of interventions for reducing the cesarean section rate and to assess the impact of this reduction on maternal and perinatal mortality and morbidity. Methods: The Cochrane Library, EMBASE, and MEDLINE were consulted from January 1990 to June 2005. Additional studies were identified by screening reference lists from identified studies and expert suggestions. Studies involving rigorous evaluation of a strategy for reducing overall cesarean section rates were identified. Randomized controlled trials, controlled before-and-after studies, and interrupted time series studies were evaluated according to Effective Practice and Organisation of Care Group criteria. Results: Among the 10 included studies, a significant reduction of cesarean section rate was found by random meta-analysis (pooled RR = 0.81 [0.75, 0.87]). No evidence of publication bias was identified. Audit and feedback (pooled RR = 0.87 [0.81, 0.93]), quality improvement (pooled RR = 0.74 [0.70, 0.77]), and multifaceted strategies (pooled RR=0.73 [0.68, 0.79]) were effective for reducing the cesarean section rate. However, quality improvement based on active management of labor showed mixed effects. Design of studies showed a higher effect for noncontrolled studies than for controlled studies (pooled RR = 0.76 [0.72, 0.81] vs 0.92 [0.88, 0.96]). Studies including an identification of barriers to change were more effective than other interventions for reducing the cesarean section rate (pooled RR = 0.74 [0.71, 0.78] vs 0.88 [0.82, 0.94]). Among included studies, no significant differences were found for perinatal and neonatal mortality and perinatal and maternal morbidity with respect to the mode of delivery. Only 1 study showed a significant reduction of neonatal and perinatal mortality (p < 0.001). Conclusions: The cesarean section rate can be safely reduced by interventions that involve health workers in analyzing and modifying their practice. Our results suggest that multifaceted strategies, based on audit and detailed feedback, are advised to improve clinical practice and effectively reduce cesarean section rates. Moreover, these findings support the assumption that identification of barriers to change is a major key to success. (BIRTH 34:1 March 2007) [source] New Contractual Relationships in the Agency Worker Market: The Case of the UK's National Health ServiceBRITISH JOURNAL OF INDUSTRIAL RELATIONS, Issue 3 2008Kim Hoque In recent years, there has been a trend towards the negotiation of closer contractual relationships between employers and employment agencies. However, little is known about this change or its likely consequences. In theory, such relationships can benefit employers by lowering fees and also reducing many of the hidden costs associated with the use of agency staff by improving the effectiveness of placement matching. Against this is the suggestion that formal partnerships are unlikely to have a positive impact given the uncertainty of demand for temporary labour and broader tendencies for risk displacement in buyer,supplier networks. In this article, our aim is to explore this matter focusing on recent developments in the UK's National Health Service. We find that new contractual relationships such as framework agreements and master vendor contracts are having mixed effects. While they serve to reduce direct costs for employers in the short term, this has been at the expense of relationship building and improvements in placement matching. These developments are also found to have some potentially negative consequences for the agency workforce itself. [source] | ||||||||||||||||||||||