950 resultados para Mixed models


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The retention and availability of water in the soil vary according to the soil characteristics and determine plant growth. Thus, the aim of this study was to evaluate water retention and availability in the soils of the State of Santa Catarina, Brazil, according to the textural class, soil class and lithology. The surface and subsurface horizons of 44 profiles were sampled in different regions of the State and different cover crops to determine field capacity, permanent wilting point, available water content, particle size, and organic matter content. Water retention and availability between the horizons were compared in a mixed model, considering the textural classes, the soil classes and lithology as fixed factors and profiles as random factors. It may be concluded that water retention is greater in silty or clayey soils and that the organic matter content is higher, especially in Humic Cambisols, Nitisols and Ferralsol developed from igneous or sedimentary rocks. Water availability is greater in loam-textured soils, with high organic matter content, especially in soils of humic character. It is lower in the sandy texture class, especially in Arenosols formed from recent alluvial deposits or in gravelly soils derived from granite. The greater water availability in the surface horizons, with more organic matter than in the subsurface layers, illustrates the importance of organic matter for water retention and availability.

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Many of the most interesting questions ecologists ask lead to analyses of spatial data. Yet, perhaps confused by the large number of statistical models and fitting methods available, many ecologists seem to believe this is best left to specialists. Here, we describe the issues that need consideration when analysing spatial data and illustrate these using simulation studies. Our comparative analysis involves using methods including generalized least squares, spatial filters, wavelet revised models, conditional autoregressive models and generalized additive mixed models to estimate regression coefficients from synthetic but realistic data sets, including some which violate standard regression assumptions. We assess the performance of each method using two measures and using statistical error rates for model selection. Methods that performed well included generalized least squares family of models and a Bayesian implementation of the conditional auto-regressive model. Ordinary least squares also performed adequately in the absence of model selection, but had poorly controlled Type I error rates and so did not show the improvements in performance under model selection when using the above methods. Removing large-scale spatial trends in the response led to poor performance. These are empirical results; hence extrapolation of these findings to other situations should be performed cautiously. Nevertheless, our simulation-based approach provides much stronger evidence for comparative analysis than assessments based on single or small numbers of data sets, and should be considered a necessary foundation for statements of this type in future.

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OBJECTIVE: We aimed to create an index to stratify cryptogenic stroke (CS) patients with patent foramen ovale (PFO) by their likelihood that the stroke was related to their PFO. METHODS: Using data from 12 component studies, we used generalized linear mixed models to predict the presence of PFO among patients with CS, and derive a simple index to stratify patients with CS. We estimated the stratum-specific PFO-attributable fraction and stratum-specific stroke/TIA recurrence rates. RESULTS: Variables associated with a PFO in CS patients included younger age, the presence of a cortical stroke on neuroimaging, and the absence of these factors: diabetes, hypertension, smoking, and prior stroke or TIA. The 10-point Risk of Paradoxical Embolism score is calculated from these variables so that the youngest patients with superficial strokes and without vascular risk factors have the highest score. PFO prevalence increased from 23% (95% confidence interval [CI]: 19%-26%) in those with 0 to 3 points to 73% (95% CI: 66%-79%) in those with 9 or 10 points, corresponding to attributable fraction estimates of approximately 0% to 90%. Kaplan-Meier estimated stroke/TIA 2-year recurrence rates decreased from 20% (95% CI: 12%-28%) in the lowest Risk of Paradoxical Embolism score stratum to 2% (95% CI: 0%-4%) in the highest. CONCLUSION: Clinical characteristics identify CS patients who vary markedly in PFO prevalence, reflecting clinically important variation in the probability that a discovered PFO is likely to be stroke-related vs incidental. Patients in strata more likely to have stroke-related PFOs have lower recurrence risk.

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Intake of caffeinated beverages might be associated with reduced cardiovascular mortality possibly via the lowering of blood pressure. We estimated the association of ambulatory blood pressure with urinary caffeine and caffeine metabolites in a population-based sample. Families were randomly selected from the general population of Swiss cities. Ambulatory blood pressure monitoring was conducted using validated devices. Urinary caffeine, paraxanthine, theophylline, and theobromine excretions were measured in 24 hours urine using ultrahigh performance liquid chromatography tandem mass spectrometry. We used mixed models to explore the associations of urinary excretions with blood pressure although adjusting for major confounders. The 836 participants (48.9% men) included in this analysis had mean age of 47.8 and mean 24-hour systolic and diastolic blood pressure of 120.1 and 78.0 mm Hg. For each doubling of caffeine excretion, 24-hour and night-time systolic blood pressure decreased by 0.642 and 1.107 mm Hg (both P values <0.040). Similar inverse associations were observed for paraxanthine and theophylline. Adjusted night-time systolic blood pressure in the first (lowest), second, third, and fourth (highest) quartile of paraxanthine urinary excretions were 110.3, 107.3, 107.3, and 105.1 mm Hg, respectively (P trend <0.05). No associations of urinary excretions with diastolic blood pressure were generally found, and theobromine excretion was not associated with blood pressure. Anti-hypertensive therapy, diabetes mellitus, and alcohol consumption modify the association of caffeine urinary excretion with systolic blood pressure. Ambulatory systolic blood pressure was inversely associated with urinary excretions of caffeine and other caffeine metabolites. Our results are compatible with a potential protective effect of caffeine on blood pressure.

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Background: Maturation of amplitude-integrated electroencephalogram (aEEG) activity is influenced by both gestational age (GA) and postmenstrual age. It is not fully known how this process is influenced by cerebral lesions. Objective: To compare early aEEG developmental changes between preterm newborns with different degrees of cerebral lesions on cranial ultrasound (cUS). Methods: Prospective cohort study on preterm newborns with GA <32.0 weeks, undergoing continuous aEEG recording during the first 84 h after birth. aEEG characteristics were qualitatively and quantitatively evaluated using pre-established criteria. Based on cUS findings three groups were formed: normal (n = 78), mild (n = 20), and severe cerebral lesions (n = 6). Linear mixed models for repeated measures were used to analyze aEEG maturational trajectories. Results: 104 newborns with a mean GA (range) 29.5 (24.4-31.7) weeks, and birth weight 1,220 (580-2,020) g were recruited. Newborns with severe brain lesions started with similar aEEG scores and tendentially lower aEEG amplitudes than newborns without brain lesions, and showed a slower development of the cyclic activity (p < 0.001), but a more rapid increase of the maximum and minimum aEEG amplitudes (p = 0.002 and p = 0.04). Conclusions: Preterm infants with severe cerebral lesions manifest a maturational delay in the aEEG cyclic activity already early after birth, but show a catch-up of aEEG amplitudes to that of newborns without cerebral lesions. Changes in the maturational aEEG pattern may be a marker of severe neurological lesions in the preterm infant.

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Exposure to fine airborne particulate matter (PM(2.5)) is associated with cardiovascular events and mortality in older and cardiac patients. Potential physiologic effects of in-vehicle, roadside, and ambient PM(2.5) were investigated in young, healthy, nonsmoking, male North Carolina Highway Patrol troopers. Nine troopers (age 23 to 30) were monitored on 4 successive days while working a 3 P.M. to midnight shift. Each patrol car was equipped with air-quality monitors. Blood was drawn 14 hours after each shift, and ambulatory monitors recorded the electrocardiogram throughout the shift and until the next morning. Data were analyzed using mixed models. In-vehicle PM(2.5) (average of 24 microg/m(3)) was associated with decreased lymphocytes (-11% per 10 microg/m(3)) and increased red blood cell indices (1% mean corpuscular volume), neutrophils (6%), C-reactive protein (32%), von Willebrand factor (12%), next-morning heart beat cycle length (6%), next-morning heart rate variability parameters, and ectopic beats throughout the recording (20%). Controlling for potential confounders had little impact on the effect estimates. The associations of these health endpoints with ambient and roadside PM(2.5) were smaller and less significant. The observations in these healthy young men suggest that in-vehicle exposure to PM(2.5) may cause pathophysiologic changes that involve inflammation, coagulation, and cardiac rhythm.

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The objective of this work was to propose a new selection strategy for the initial stages of sugarcane improvement, based on the methodology 'simulated individual BLUP (BLUPIS)', which promotes a dynamic allocation of individuals selected in each full-sib family, using BLUP as a base for both the genotypic effects of the referred families and plot effects. The method proposed applies to single full-sib families or those obtained from unbalanced or balanced diallel crosses, half-sib families and self-pollinated families. BLUPIS indicates the number of individuals to be selected within each family, the total number of clones to be advanced, and the number of families to contribute with selected individuals. Correlation between BLUPIS and true BLUP was 0.96, by method validation. Additionally, BLUPIS allows the identification of which replication contains the best individuals of each family.

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BACKGROUND: The epidemiology of respiratory viruses and their potential clinical impact when recovered in lower respiratory specimens has not been established in the hospital setting. A study was performed to investigate the association between positive viral detection and respiratory infection in an at-risk population. METHODS: 299 adult patients who underwent bronchoalveolar lavage (BAL) procedures were enrolled in a hospital-based prospective cohort study. Descriptive epidemiology is presented of 17 different respiratory viruses detected by reverse transcription-polymerase chain reaction assays in BAL fluid specimens. Multivariate analysis was conducted to identify the clinical characteristics independently associated with the presence of virus. RESULTS: Of 522 BAL fluid specimens analysed, 81% were collected in adult transplant recipients or other immunocompromised patients. Overall, PCR assays identified viral nucleic acid in 91 BAL fluid samples (17.4%). Similar rates of virus-positive BAL fluid were found in the different subpopulations studied (p = 0.113). Coronaviruses were the most frequent (32.3%), followed by rhinovirus (22.6%), parainfluenza (19.5%), influenza (9.7%), respiratory synctial virus (8.6%), human metapneumovirus (4.2%) and bocavirus (3.1%). Multivariate analysis using mixed models showed that respiratory viral infections were associated with a lack of antibiotic treatment response (OR 2.2, 95% CI 1.2 to 4.1) and the absence of radiological infiltrate (OR 0.3, 95% CI 0.2 to 0.8). In lung transplant recipients in whom a respiratory infection was suspected, the respiratory viral detection rate was 24.4% compared with 13.8% overall in other patients (p = 0.02). CONCLUSIONS: In this cohort of hospitalised adults, respiratory viruses detected in BAL fluid specimens were associated with respiratory symptoms, absence of radiological infiltrates and a poor response to antibiotic therapy.

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In a system where tens of thousands of words are made up of a limited number of phonemes, many words are bound to sound alike. This similarity of the words in the lexicon as characterized by phonological neighbourhood density (PhND) has been shown to affect speed and accuracy of word comprehension and production. Whereas there is a consensus about the interfering nature of neighbourhood effects in comprehension, the language production literature offers a more contradictory picture with mainly facilitatory but also interfering effects reported on word production. Here we report both of these two types of effects in the same study. Multiple regression mixed models analyses were conducted on PhND effects on errors produced in a naming task by a group of 21 participants with aphasia. These participants produced more formal errors (interfering effect) for words in dense phonological neighbourhoods, but produced fewer nonwords and semantic errors (a facilitatory effect) with increasing density. In order to investigate the nature of these opposite effects of PhND, we further analysed a subset of formal errors and nonword errors by distinguishing errors differing on a single phoneme from the target (corresponding to the definition of phonological neighbours) from those differing on two or more phonemes. This analysis confirmed that only formal errors that were phonological neighbours of the target increased in dense neighbourhoods, while all other errors decreased. Based on additional observations favouring a lexical origin of these formal errors (they exceeded the probability of producing a real-word error by chance, were of a higher frequency, and preserved the grammatical category of the targets), we suggest that the interfering effect of PhND is due to competition between lexical neighbours and target words in dense neighbourhoods.

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PURPOSE: Diisononyl phthalate (DiNP) is primarily used as a plasticizer in polyvinyl chloride (PVC) materials. While information is available on general population exposure to DiNP, occupational exposure data are lacking. We present DiNP metabolite urinary concentrations in PVC processing workers, estimate DiNP daily intake for these workers, and compare worker estimates to other populations. METHODS: We assessed DiNP exposure in participants from two companies that manufactured PVC materials, a PVC film manufacturer (n = 25) and a PVC custom compounder (n = 12). A mid-shift and end-shift urine sample was collected from each participant and analyzed for the DiNP metabolite mono(carboxy-isooctyl) phthalate (MCiOP). Mixed models were used to assess the effect on MCiOP concentrations of a worker being assigned to (1) a task using DiNP and (2) a shift where DiNP was used. A simple pharmacokinetic model was used to estimate DiNP daily intake from the MCiOP concentrations. RESULTS: Creatinine-adjusted MCiOP urinary concentrations ranged from 0.42-80 μg/g in PVC film and from 1.11-13.4 μg/g in PVC compounding. PVC film participants who worked on a task using DiNP (n = 7) had the highest MCiOP geometric mean (GM) end-shift concentration (25.2 μg/g), followed by participants who worked on a shift where DiNP was used (n = 11) (17.7 μg/g) as compared to participants with no task (2.92 μg/g) or shift (2.08 μg/g) exposure to DiNP. The GM end-shift MCiOP concentration in PVC compounding participants (4.80 μg/g) was comparable to PVC film participants with no task or shift exposure to DiNP. Because no PVC compounding participants were assigned to tasks using DINP on the day sampled, DiNP exposure in this company may be underestimated. The highest DiNP intake estimate was 26 μg/kg/day. CONCLUSION: Occupational exposure to DiNP associated with PVC film manufacturing tasks were substantially higher (sixfold to tenfold) than adult general population exposures; however, all daily intake estimates were less than 25% of current United States or European acceptable or tolerable daily intake estimates. Further characterization of DiNP occupational exposures in other industries is recommended.

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The objetive of this work was to evaluate the influence of intergenotypic competition in open-pollinated families of Eucalyptus and its effects on early selection efficiency. Two experiments were carried out, in which the timber volume was evaluated at three ages, in a randomized complete block design. Data from the three years of evaluation (experiment 1, at 2, 4, and 7 years; and experiment 2, at 2, 5, and 7 years) were analyzed using mixed models. The following were estimated: variance components, genetic parameters, selection gains, effective number, early selection efficiency, selection gain per unit time, and coincidence of selection with and without the use of competition covariates. Competition effect was nonsignificant for ages under three years, and adjustment using competition covariates was unnecessary. Early selection for families is effective; families that have a late growth spurt are more vulnerable to competition, which markedly impairs ranking at the end of the cycle. Early selection is efficient according to all adopted criteria, and the age of around three years is the most recommended, given the high efficiency and accuracy rate in the indication of trees and families. The addition of competition covariates at the end of the cycle improves early selection efficiency for almost all studied criteria.

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Alteration of natural habitats as a result of agricultural intensification is detrimental for wildlife. There is, however, growing evidence that land use and management can be wildlife friendly. In Europe, agricultural areas cover two-thirds of the land and therefore play a major role in maintaining biodiversity. Agricultural land use is very intense in vineyard-dominated landscapes but there are no refuges for wildlife in the form of ecological compensation areas. In our study, we assessed spatial variation in abundance of salamander (Salamandra salamandra) larvae in relation to land use and stream characteristics in vineyard-dominated landscapes. Abundance of larval salamanders depended positively on weirs, amount of riparian vegetation along the streams and environment-friendly agricultural practice in the vineyards. Surprisingly, road density also had positive effects, presumably through indirect effects (stone walls along roads may serve as refugia). Thus, abundance is determined by characteristics of both the aquatic and terrestrial habitats. Our results suggest that fire salamanders can persist in landscapes dominated by intensive agriculture like viticulture, indicate wildlife-friendly management options and highlight that man-made habitat can be valuable for wildlife.

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OBJECTIVE: To evaluate the variability of bond strength test results of adhesive systems (AS) and to correlate the results with clinical parameters of clinical studies investigating cervical restorations. MATERIALS AND METHODS: Regarding the clinical studies, the internal database which had previously been used for a meta-analysis on cervical restorations was updated with clinical studies published between 2008 and 2012 by searching the PubMed and SCOPUS databases. PubMed and the International Association for Dental Research abstracts online were searched for laboratory studies on microtensile, macrotensile and macroshear bond strength tests. The inclusion criteria were (1) dentin, (2) testing of at least four adhesive systems, (3) same diameter of composite and (4) 24h of water storage prior to testing. The clinical outcome variables were retention loss, marginal discoloration, detectable margins, and a clinical index comprising the three parameters by weighing them. Linear mixed models which included a random study effect were calculated for both, the laboratory and the clinical studies. The variability was assessed by calculating a ratio of variances, dividing the variance among the estimated bonding effects obtained in the linear mixed models by the sum of all variance components estimated in these models. RESULTS: Thirty-two laboratory studies fulfilled the inclusion criteria comprising 183 experiments. Of those, 86 used the microtensile test evaluating 22 adhesive systems (AS). Twenty-seven used the macrotensile test with 17 AS, and 70 used the macroshear test with 24 AS. For 28 AS the results from clinical studies were available. Microtensile and macrotensile (Spearman rho=0.66, p=0.007) were moderately correlated and also microtensile and macroshear (Spearman rho=0.51, p=0.03) but not macroshear and macrotensile (Spearman rho=0.34, p=0.22). The effect of the adhesive system was significant for microtensile and macroshear (p<0.001) but not for macrotensile. The effect of the adhesive system could explain 36% of the variability of the microtensile test, 27% of the macrotensile and 33% of the macroshear test. For the clinical trials, about 49% of the variability of retained restorations could be explained by the adhesive system. With respect to the correlation between bond strength tests and clinical parameters, only a moderate correlation between micro- and macrotensile test results and marginal discoloration was demonstrated. However, no correlation between these tests and a retention loss or marginal integrity was shown. The correlation improved when more studies were included compared to assessing only one study. SIGNIFICANCE: The high variability of bond strength test results highlights the need to establish individual acceptance levels for a given test institute. The weak correlation of bond-strength test results with clinical parameters leads to the conclusion that one should not rely solely on bond strength tests to predict the clinical performance of an adhesive system but one should conduct other laboratory tests like tests on the marginal adaptation of fillings in extracted teeth and the retention loss of restorations in non-retentive cavities after artificial aging.

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AIM: Longitudinal studies that have examined cognitive performance in children with intellectual disability more than twice over the course of their development are scarce. We assessed population and individual stability of cognitive performance in a clinical sample of children with borderline to mild non-syndromic intellectual disability. METHOD: Thirty-six children (28 males, eight females; age range 3-19y) with borderline to mild intellectual disability (Full-scale IQ [FSIQ] 50-85) of unknown origin were examined in a retrospective clinical case series using linear mixed models including at least three assessments with standardized intelligence tests. RESULTS: Average cognitive performance remained remarkably stable over time (high population stability, drop of only 0.38 IQ points per year, standard error=0.39, p=0.325) whereas individual stability was at best moderate (intraclass correlation of 0.58), indicating that about 60% of the residual variation in FSIQ scores can be attributed to between-child variability. Neither sex nor socio-economic status had a statistically significant impact on FSIQ. INTERPRETATION: Although intellectual disability during childhood is a relatively stable phenomenon, individual stability of IQ is only moderate, likely to be caused by test-to-test reliability (e.g. level of child's cooperation, motivation, and attention). Therefore, clinical decisions and predictions should not rely on single IQ assessments, but should also consider adaptive functioning and previous developmental history.

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The Spanish Barley Breeding Program is carried out by four public research organizations, located at the most representative barley growing regions of Spain. The aim of this study is to evaluate the program retrospectively, attending to: i) the progress achieved in grain yield, and ii) the extent and impact of genotype-by-environment interaction of grain yield. Grain yields and flowering dates of 349 advanced lines in generations F8, F9 and F10, plus checks, tested at 163 trials over 11 years were analized. The locations are in the provinces of Albacete, Lleida, Valladolid and Zaragoza. The data are highly unbalanced because the lines stayed at the program for a maximum of three years. Progress was estimated using relative grain yield and mixed models (REML) to homogenize the results among years and locations. There was evident progress in the program over the period studied, with increasing relative yields in each generation, and with advanced lines surpassing the checks in the last two generations, although the rate of progress was uneven across locations. The genetic gain was greater from F8 to F9 than from F9 to F10. The largest non-purely environmental component of variance was genotype-by-location-by-year, meaning that the genotype-by-location pattern was highly unpredictable. The relationship between yield and flowering time overall was weak in the locations under study at this advanced stage of the program. The program can be continued with the same structure, although measures should be taken to explore the causes of slower progress at certain locations.