Search results for "Random effects"
showing 10 items of 55 documents
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.
Bayesian longitudinal models for paediatric kidney transplant recipients
2015
Chronic kidney disease is a progressive loss of renal function which results in the inability of the kidneys to properly filter waste from the blood. Renal function is usually estimated by the glomerular filtration rate (eGFR), which decreases with the worsening of the disease. Bayesian longitudinal models with covariates, random effects, serial correlation and measurement error are discussed to analyse the progression of eGFR in first transplanted children taken from a study in Valencia, Spain.
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…
On Ignoring the Random Effects Assumption in Multilevel Models: Review, Critique, and Recommendations
2019
Entities such as individuals, teams, or organizations can vary systematically from one another. Researchers typically model such data using multilevel models, assuming that the random effects are uncorrelated with the regressors. Violating this testable assumption, which is often ignored, creates an endogeneity problem thus preventing causal interpretations. Focusing on two-level models, we explain how researchers can avoid this problem by including cluster means of the Level 1 explanatory variables as controls; we explain this point conceptually and with a large-scale simulation. We further show why the common practice of centering the predictor variables is mostly unnecessary. Moreover, …
Bayesian reanalysis of a quantitative trait locus accounting for multiple environments by scaling in broilers1
2006
A Bayesian method was developed to handle QTL analyses of multiple experimental data of outbred populations with heterogeneity of variance between sexes for all random effects. The method employed a scaled reduced animal model with random polygenic and QTL allelic effects. A parsimonious model specification was applied by choosing assumptions regarding the covariance structure to limit the number of parameters to estimate. Markov chain Monte Carlo algorithms were applied to obtain marginal posterior densities. Simulation demonstrated that joint analysis of multiple environments is more powerful than separate single trait analyses of each environment. Measurements on broiler BW obtained from…
How common is bipolar disorder in general primary care attendees? A systematic review and meta-analysis investigating prevalence determined according…
2016
Objective: There are mounting calls for bipolar disorder to be managed in primary care, yet the exact prevalence remains unclear. We conducted a meta-analysis to investigate the prevalence of bipolar disorder in general primary care attendees without other comorbid psychiatric diagnosis. Method: We systematically searched major electronic databases from inception till 03/2015. Articles were included that reported the prevalence of bipolar disorder determined in line with structured clinical assessment in primary care settings. Two independent authors conducted searches, completed methodological appraisal and extracted data. A random effects meta-analysis and meta-regression were performed. …
Mortality associated with cardiovascular disease in patients with COVID-19
2020
Introducción y objetivos: Las enfermedades cardiovasculares (ECV) se han identificado como un factor de riesgo de mal pronóstico en pacientes con infección por COVID-19. Métodos: Se realizó un metanálisis de estudios actualmente disponibles con la prevalencia de ECV en supervivientes frente a no supervivientes en pacientes con infección por COVID-19 hasta el 16 de julio de 2020. Los análisis se realizaron mediante un modelo de efectos aleatorios y sensibilidad. Se realizaron análisis para identificar posibles fuentes de heterogeneidad o evaluar los efectos de los estudios pequeños. Resultados: Se incluyó a 307.596 pacientes de 16 estudios, de los que 46.321 (15,1%) tenían ECV. La tasa de mo…
Effects of motor imagery on strength, range of motion, physical function, and pain intensity in patients with total knee arthroplasty: A systematic r…
2021
Abstract Background In the early stages of total knee arthroplasty (TKA) rehabilitation, in which physical function in general can be affected, motor imagery (MI) might play a relevant role. Objective To assess the impact of MI on strength, active range of motion (ROM), pain intensity, and physical function in patients with TKA. Methods We conducted a systematic review and meta-analysis of randomised controlled trials. Pooled effects were calculated as standardised mean differences (SMDs) and 95% confidence intervals (CIs) for the relevant outcomes using random effects model. The certainty of evidence was assessed with GRADE approach. Results This review included 7 articles. The addition of…
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…
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…