1,721,252 research outputs found
Modelling normative kinetic perimetry isopters using mixed-effects quantile regression
Get PDFKinetic perimetry is used to quantify visual field size/sensitivity. Clinically, perimetry can be used to diagnose and monitor ophthalmic and neuro-ophthalmic disease. Normative data are integral to the interpretation of these findings. However, there are few computational developments that allow clinicians to collect and analyze normative data from kinetic perimeters. In this article we describe an approach to fitting kinetic responses using linear quantile mixed models. Analogously to traditional linear mixed-effects models for the mean, linear quantile mixed models account for repeated measurements taken from the same individual, but differently from linear mixed-effects models, they are more flexible as they require weaker distributional assumptions and allow for quantile-specific inference. Our approach improves on parametric alternatives based on normal assumptions. We introduce the R package kineticF, a freely available and open-access resource for the analysis of perimetry data. Our proposed approach can be used to analyze normative data from further studies
Aranda-Ordaz quantile regression for student performance assessment
No full textIn education research, normal regression models may not be appropriate due to the presence of boundedvariables, which may exhibit a large variety of distributional shapes and present floor and ceiling effects.In this article a class of quantile regression models for bounded response variables is developed. The one-parameter Aranda-Ordaz symmetric and asymmetric families of transformations are applied to addressmodelling issues that arise when estimating conditional quantiles of a bounded response variable whoserelationship with the covariates is possibly nonlinear. This approach exploits the equivariance property ofquantiles and aims at achieving linearity of the predictor. This offers a flexible model-based alternativeto nonparametric estimation of the quantile function. Since the transformation is quantile-specific, themodelling takes into account the local features of the conditional distribution of the response variable.Our study is motivated by the analysis of reading performance in seven-year old children part of theMillennium Cohort Study
Time to undetectable viral load after highly active antiretroviral therapy initiation among HIV-infected pregnant women
No full textAbstract: Background. There have been no clinical trials in resource-rich regions that have addressed the question of which highly active antiretroviral therapy (HAART) regimens are more effective for optimal viral response in antiretroviral-naive, human immunodeficiency virus (HIV)-infected pregnant women.
Methods. Data on 240 HIV-1-infected women starting HAART during pregnancy who were enrolled in the prospective European Collaborative Study from 1997 through 2004 were analyzed. An interval-censored survival model was used to assess whether factors, including type of HAART regimen, race, region of birth, and baseline immunological and virological status, were associated with the duration of time necessary to suppress viral load below undetectable levels before delivery of a newborn.
Results. Protease inhibitor-based HAART was initiated in 156 women (65%), 125 (80%) of whom received nelfinavir, and a nevirapine-based regimen was initiated in the remaining 84 women (35%). Undetectable viral loads were achieved by 73% of the women by the time of delivery. Relative hazards of time to achieving viral suppression were 1.54 (95% confidence interval, 1.05-2.26) for nevirapine-based HAART versus PI-based regimens and 1.90 (95% confidence interval, 1.16-3.12) for western African versus non-African women. The median duration of time from HAART initiation to achievement of an undetectable viral load was estimated to be 1.4 times greater in women receiving PI-based HAART, compared with women receiving nevirapine-based HAART. Baseline HIV RNA load was also a significant predictor of the rapidity of achieving viral suppression by delivery, but baseline immune status was not.
Conclusions. In this study, nevirapine-based HAART (compared with PI [mainly nelfinavir]-based HAART), western African origin, and lower baseline viral load were associated with shorter time to achieving viral suppression
Using functional data analysis to understand daily activity levels and patterns in primary school-aged children: Cross-sectional analysis of a UK-wide study
Get PDFTemporal characterisation of physical activity in children is require df oreffectivs strategie sto increase physical activity(PA)
Time to undetectable viral load after highly active antiretroviral therapy initiation among HIV-infected pregnant women.
No full text(BUFFOLANO W, COLLABORATOR
Modelling accelerometer data from 7-year old British children using functional analysis of variance
No full textImprovements in virological control among women conceiving on combination antiretroviral therapy in Western Europe.
No full textInsufficient antiretroviral therapy in pregnancy: missed opportunities for prevention of mother-to-child transmission of HIV in Europe.
No full text- …
