Search results for "Covariate"
showing 10 items of 110 documents
The effect of peer socioeconomic status on student achievement: a meta-analysis
2010
Previous studies on the effects on students’ test scores of their peers’ socioeconomic status (SES) have reported varying results. In order to understand why researchers have alternately found small effects, large effects, or no effects at all, a meta-regression analysis including an extensive database of 30 studies on the topic was conducted. Results show that the size of the compositional effect that researchers find is strongly related to how they measure SES and to their choice of model. Measuring SES dichotomously (e.g. free lunch eligibility) or including several average SES variables in one model leads to smaller effect estimates than using a thoroughly constructed composite that inc…
Transforming RNA-Seq Data to Improve the Performance of Prognostic Gene Signatures
2014
Gene expression measurements have successfully been used for building prognostic signatures, i.e for identifying a short list of important genes that can predict patient outcome. Mostly microarray measurements have been considered, and there is little advice available for building multivariable risk prediction models from RNA-Seq data. We specifically consider penalized regression techniques, such as the lasso and componentwise boosting, which can simultaneously consider all measurements and provide both, multivariable regression models for prediction and automated variable selection. However, they might be affected by the typical skewness, mean-variance-dependency or extreme values of RNA-…
Self-rated health and mortality in older men and women: A time-dependent covariate analysis
2007
Although the relation between self-rated health (SRH) and mortality is widely known, most of the studies have relied in baseline measurements unheeding the dynamics of the phenomenon. Our aim was to analyze how SRH both as a constant and as a time-dependent covariate predicts mortality in older men and women and to compare these different approaches. Subjects consisted of 110 male and 208 female (n = 318) residents in the city of Jyvaskyla, central Finland, aged 75 years at the baseline in 1989. The follow-up data was gathered in 1994 and mortality was followed for 10 years. Results showed that poor SRH was strongly associated with higher mortality risk in women in all models. In men, the a…
Customized and non-customized live-born birth-weight curves of single and uncomplicated pregnancies from the Burgundy perinatal network. Part I – met…
2017
International audience; Objectives: To establish non-customized and customized birth-weight curves of single and uncomplicated pregnancies according to gestational age.Materials and methods: We used data for 64,173 mother-infants pairs from the Burgundy perinatal network database (France) over the period 2005-2013. A validated procedure was used to link mothers with their newborns, and maternal and fetal pathologies likely to affect birth weight were excluded. Multiple regression analysis with covariate selection was used to build a customized growth curve with maternal and fetal parameters.Results: Using this methodology, three different curves were generated: an unadjusted curve for birth…
Empirical study of the dependence of the results of multivariable flexible survival analyses on model selection strategy
2008
Flexible survival models, which avoid assumptions about hazards proportionality (PH) or linearity of continuous covariates effects, bring the issues of model selection to a new level of complexity. Each ‘candidate covariate’ requires inter-dependent decisions regarding (i) its inclusion in the model, and representation of its effects on the log hazard as (ii) either constant over time or time-dependent (TD) and, for continuous covariates, (iii) either loglinear or non-loglinear (NL). Moreover, ‘optimal’ decisions for one covariate depend on the decisions regarding others. Thus, some efficient model-building strategy is necessary. We carried out an empirical study of the impact of the model …
Spatial Interaction between Neighbouring Counties: Cancer Mortality Data in Valencia (Spain)
1995
The statistical analysis of geographical mortality data has usually been approached via regression models that include appropriate covariates. These models assume stochastic independence of mortality counts for neighbouring sites, a questionable assumption that spatial automodels (Besag, 1974, Journal of the Royal Statistical Society, Series B 36, 192-236) make unnecessary. This paper presents the use of the autopoisson distribution in order to detect spatial interaction between neighbouring sites. If this interaction results in being nonsignificant, the auto-Poisson distribution reduces to a usual Poisson regression model, a particular case of generalized linear models (McCullagh and Nelde…
Comparing cetacean abundance estimates derived from spatial models and design-based line transect methods
2007
Spatial modelling is increasingly being used as an alternative to conventional design- based line transect sampling to estimate cetacean abundance. This new method combines line transect sampling with spatial analysis to predict animal abundance based on the relationship of ani- mals observed to environmental factors. It presents several advantages including: (1) the ability to use data collected from 'platforms of opportunity', (2) the ability to estimate abundance for any defined subarea within the study area, and (3) the possibility for increased precision if covariates explain sufficient variability in the data. One study has been conducted to compare spatial modelling with conventional…
Population pharmacokinetic model of lithium and drug compliance assessment.
2016
Population pharmacokinetic analysis of lithium during therapeutic drug monitoring and drug compliance assessment was performed in 54 patients and 246 plasma concentrations levels were included in this study. Patients received several treatment cycles (1-9) and one plasma concentration measurement for each patient was obtained always before starting next cycle (pre-dose) at steady state. Data were analysed using the population approach with NONMEM version 7.2. Lithium measurements were described using a two-compartment model (CL/F=0.41Lh-1, V1/F=15.3L, Q/F=0.61Lh-1, and V2/F = 15.8L) and the most significant covariate on lithium CL was found to be creatinine clearance (reference model). Lith…
An Ordinal Joint Model for Breast Cancer
2017
We propose a Bayesian joint model to analyze 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 and the time-to-event process through a left-truncated Cox proportional hazards model with information of the longitudinal marker and baseline covariates. Both longitudinal and survival processes are connected by a common vector of random effects.
Individual participant data systematic reviews with meta-analyses of psychotherapies for borderline personality disorder: A protocol
2020
AbstractIntroductionThe heterogeneity in people with BPD and the range of specialised psychotherapies means that people with certain BPD characteristics might benefit more or less from different types of psychotherapy. Identifying moderating characteristics of individuals is a key to refine and tailor standard treatments so they match the specificities of the individual patient. The objective of this is to improve the quality of care and the individual outcomes. Thus, the aim of the current reviews is to investigate potential predictors and moderating patient characteristics on treatment outcomes for patients with BPD.Methods and analysisOur primary meta-analytic method will be the one-stag…