Search results for "random effects"
showing 10 items of 55 documents
Bayesian joint ordinal and survival modeling for breast cancer risk assessment
2016
We propose a joint model to analyze the structure and intensity of the association between longitudinal measurements of an ordinal marker and time to a relevant event. The longitudinal process is defined in terms of a proportional-odds cumulative logit model. Time-to-event is modeled through a left-truncated proportionalhazards model, which incorporates information of the longitudinal marker as well as baseline covariates. Both longitudinal and survival processes are connected by means of a common vector of random effects. General inferences are discussed under the Bayesian approach and include the posterior distribution of the probabilities associated to each longitudinal category and the …
Long-term experiments and strip plot designs
2015
In a long-term experiment usually the experimenter needs to know whether the effect of a treatment varies over time. But time usually has both a fixed and a random effects over the output and the difficulty in the analysis depends on the particular design considered and the availability of covariates. Actually, as shown in the paper, the presence of covariates can be very useful to model the random effect of time. In this paper a model to analyze data from a long-term strip plot design with covariates is proposed. Its effectiveness will be tested using both simulated and real data from a crop rotation experiment.
Even a low-dose of moderate-to-vigorous physical activity reduces mortality by 22% in adults aged ≥60 years: a systematic review and meta-analysis
2015
Type de document : revue de littérature; International audience; Background The health benefits of 150 min a week of moderate-to-vigorous-intensity physical activity (MVPA) in older adults, as currently recommended, are well established, but the suggested dose in older adults is often not reached.Objectives We aimed to determine whether a lower dose of MVPA was effective in reducing mortality, in participants older than 60 years.Methods The PubMed and Embase databases were searched from inception to February 2015. Only prospective cohorts were included. Risk ratios of death were established into four doses based on weekly Metabolic Equivalent of Task (MET)-minutes, defined as inactive (refe…
Determinantes de la estructura de vencimiento de la deuda en las empresas no cotizadas de los sectores industrial y de la construcción en Colombia de…
2017
Este artículo de reflexión explora, analiza y formula evidencias empíricas en torno a las variables determinantes del plazo del endeudamiento (corto plazo) de las empresas no cotizadas de los sectores industrial y de la construcción en Colombia para el periodo de 2008 a 2014. De acuerdo con el procesamiento de la información contable y financiera anual de las empresas de estos sectores que están reportadas en el Sistema de Información y Reporte Empresarial (Sirem) de la Superintendencia de Sociedades, se construye una base de datos con dos paneles desbalanceados para cada sector. Posteriormente, dicha información es modelada estocásticamente, estimándose las variables para cada sector por m…
Preemptive analgesia in dental implant surgery: A systematic review and meta-analysis of randomized controlled trials
2021
Background To assess the effectiveness of preemptive analgesia in dental implant surgery in randomized controlled trials (RCTs). Material and Methods The present study was conducted in accordance with the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement and registered in PROSPERO database CRD42020168757. A search without restrictions regarding language or date of publication was conducted in six databases and gray literature. A random effect meta-analysis compared the efficacy of preemptive analgesia compared to placebo through pooled OR and 95%CI. The interpretation of results followed the certainty of evidence using the Grading of Rec…
University student talent: the real driver for performance?
2017
Investigation about the university student performance, and its measurement, are very crucial issues for any policy maker. Since the economic crisis, jobs market requires even higher skills and competences. Literature offers a lot of papers about the university student quality and performance, in order to identify the main determinants of them. Often, results are very different, and they seems to hold just in a specific context. This paper aims to investigate the role of a latent variable that can take into account the student motivation, aptitude, and abilities, here conveniently called talent. A random effect Quantile Regression on a new measure of Italian student performance has been ado…
A decade of trials of interferon-alpha for chronic hepatitis C. A meta-regression analysis
2003
The most relevant randomized controlled trials of interferon-alpha (IFN) for naive patients with chronic hepatitis C (CHC) published in a decade, just before appearance of pegylated IFN trials in 2000, were included in this paper. Its purpose is to review the relationship between sustained biochemical response in active versus control group versus usual clinical variables as IFN regimens, cirrhosis, genotype and versus less frequently addressed variables as funding, methodological quality or location of principal author. Meta-analysis estimates of global treatment effect varied according to trial design: group 1=IFN versus placebo/no treatment, 32 RCTs, 2499 pts, OR 9.5 (6.3-14.2); group 2a…
Bayesian hierarchical nonlinear modelling of intra-abdominal volume during pneumoperitoneum for laparoscopic surgery
2021
Laparoscopy is an operation carried out in the abdomen or pelvis through small incisions with external visual control by a camera. This technique needs the abdomen to be insufflated with carbon dioxide to obtain a working space for surgical instruments' manipulation. Identifying the critical point at which insufflation should be limited is crucial to maximizing surgical working space and minimizing injurious effects. Bayesian nonlinear growth mixed-effects models are applied to data coming from a repeated measures design. This study allows to assess the relationship between the insufflation pressure and the intra--abdominal volume.
A new approach for estimating a nonlinear growth component in multilevel modeling
2011
This study presents a new approach to estimation of a nonlinear growth curve component with fixed and random effects in multilevel modeling. This approach can be used to estimate change in longitudinal data, such as day-of-the-week fluctuation. The motivation of the new approach is to avoid spurious estimates in a random coefficient regression model due to the synchronized periodical effect (e.g., day-of-the-week fluctuation) appearing both in independent and dependent variables. First, the new approach is introduced. Second, a Monte Carlo simulation study is carried out to examine the functioning of the proposed new approach in the case of small sample sizes. Third, the use of the approac…
Time-to-event analysis of mastitis at first-lactation in Valle del Belice ewes
2007
A time-to-event study for mastitis at first-lactation in Valle del Belice ewes was conducted, using survival analysis with an animal model. The goals were to evaluate the effect of lambing season and level of milk production on the time from lambing to the day when a ewe experienced a test-day with a recorded SCC greater than or equal to 750,000 cells/ml, and to estimate, for this trait, its heritability and the percentage of variation explained by the flock-year of lambing effect. A dataset with 2468 first-lactation records, collected from 1998 to 2003 in Valle del Belice ewes allocated in 17 flocks, was used. The Cox model used included lambing season and total milk yield adjusted for lac…