617 research outputs found
Modelling normative kinetic perimetry isopters using mixed-effects quantile regression
No full textKinetic 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
Antenatal atazanavir: a retrospective analysis of pregnancies exposed to atazanavir.
No full textINTRODUCTION: There are few data regarding the tolerability, safety, or efficacy of antenatal atazanavir. We report our clinical experience of atazanavir use in pregnancy.
METHODS: A retrospective medical records review of atazanavir-exposed pregnancies in 12 London centres between 2004 and 2010.
RESULTS: There were 145 pregnancies in 135 women: 89 conceived whilst taking atazanavir-based combination antiretroviral therapy (cART), "preconception" atazanavir exposure; 27 started atazanavir-based cART as "first-line" during the pregnancy; and 29 "switched" to an atazanavir-based regimen from another cART regimen during pregnancy. Gastrointestinal intolerance requiring atazanavir cessation occurred in five pregnancies. Self-limiting, new-onset transaminitis was most common in first-line use, occurring in 11.0%. Atazanavir was commenced in five switch pregnancies in the presence of transaminitis, two of which discontinued atazanavir with persistent transaminitis. HIV-VL < 50 copies/mL was achieved in 89.3% preconception, 56.5% first-line, and 72.0% switch exposures. Singleton preterm delivery (<37 weeks) occurred in 11.7% preconception, 9.1% first-line, and 7.7% switch exposures. Four infants required phototherapy. There was one mother-to-child transmission in a poorly adherent woman.
CONCLUSIONS: These data suggest that atazanavir is well tolerated and can be safely prescribed as a component of combination antiretroviral therapy in pregnancy
Julian Stander, Katerina Tzioli and Mario Cortina Borja: 200 years of Greek independence… and PMs
No full textQuality Control Methods in Accelerometer Data Processing: Defining Minimum Wear Time
No full textWhen using accelerometers to measure physical activity, researchers need to determine whether subjects have worn their device for a sufficient period to be included in analyses. We propose a minimum wear criterion using population-based accelerometer data, and explore the influence of gender and the purposeful inclusion of children with weekend data on reliability. of 0.8 is often regarded as acceptable reliability. Analyses were repeated on data from children who met different minimum daily wear times (one to 10 hours) and wear days (one to seven days). Analyses were conducted for all children, separately for boys and girls, and separately for children with and without weekend data. = 6,528) was achieved when children with ≥ two days lasting ≥10 hours/day were included in analyses. Reliability coefficients were similar for both genders. Purposeful sampling of children with weekend data resulted in comparable reliabilities to those calculated independent of weekend wear.Quality control procedures should be undertaken before analysing accelerometer data in large-scale studies. Using data from children with ≥ two days lasting ≥10 hours/day should provide reliable estimates of physical activity. It’s unnecessary to include only children with accelerometer data collected during weekends in analyses
Age related standards for total lymphocyte, CD4+ and CD8+ cell counts in children born in europe
No full textOBJECTIVE: Currently used reference values for immunologic markers in children are largely derived from cross-sectional data from historic, small sample size studies in predominantly white children. There is a lack of reliable age-related standards for immunologic markers, such as CD4+ cell counts, in particular in black children whose values according to recent reports may differ from those in white children. Standards are essential for diagnosing and monitoring childhood diseases such as pediatric human immunodeficiency virus (HIV) infection. DESIGN: Prospective cohort study with data on 1781 uninfected children born to HIV-infected mothers in the European Collaborative Study. METHODS: Age-related standards (centiles) for immunologic markers (CD4+ and CD8+ cell counts and total lymphocyte counts) up to 5 years in black and up to 10 years in white children were constructed using Generalized Additive Models for Location, Scale and Shape method, which allows for variability and skewness of the data. The optimal model was chosen according to the Akaike Information Criterion. RESULTS: Patterns and values of total lymphocyte, CD4+ and CD8+ cell counts varied with age, especially in the first 3 years of life, but less so thereafter. Values of all 3 immunologic markers were substantially and significantly lower in black than in white children of the same age. CONCLUSIONS: We present age-related standards separately for black and white children to aid clinicians in the monitoring of childhood diseases. These standards may also contribute to the decision on an accurate cutoff for CD4+ cell counts for initiating treatment of HIV-infected children
Using functional data analysis to understand daily activity levels and patterns in primary school-aged children: Cross-sectional analysis of a UK-wide study
No full textTemporal characterisation of physical activity in children is require df oreffectivs strategie sto increase physical activity(PA)
Modelling accelerometer data from 7-year old British children using functional analysis of variance
No full textEnvironmental influences on children’s physical activity
No full textThis paper aims to assess whether7-year-olds’physical activity is associated with familyand area-level measures of the physical andsocioeconomic environments.MethodsWe analysed the association of environmentswith physical activity in 6497 singleton children from theUK Millennium Cohort Study with reliable accelerometerdata (≥2 days and≥10 h/day). Activity levels wereassessed as counts per minute; minutes of moderate tovigorous activity (MVPA); and whether meetingrecommended guidelines (≥60 min/day MVPA).ResultsHigher levels of children’s physical activity wereassociated with households without use of a car andwith having a television in a child’s bedroom (for countsper minute only). Aspects of the home socioeconomicenvironment that were associated with more children’sphysical activity were lone motherhood, lower maternalsocioeconomic position and education, family incomebelow 60% national median, and not owning the home.Children’s activity levels were higher when parentsperceived their neighbourhood as poor for bringing upchildren and also when families were living in the mostdeprived areas. Relationships were independent ofcharacteristics such as child’s body mass index andethnic group. When adjusted for physical andsocioeconomic correlates, the factors remainingsignificant in all outcomes were: household car usageand maternal education.ConclusionsAlthough physical and socioeconomicenvironments are associated with children’s physicalactivity, much of the variation appears to be determinedby the child’s home socioeconomic circumstances ratherthan the wider environment where they live
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