Multilevel model with random effects for clustered survival data with multiple failure outcomes.

We present a multilevel frailty model for handling serial dependence and simultaneous heterogeneity in survival data with a multilevel structure attributed to clustering of subjects and the presence of multiple failure outcomes. One commonly observes such data, for example, in multi-institutional, randomized placebo-controlled trials in which patients suffer repeated episodes (eg, recurrent migraines) of the disease outcome being measured. The model extends the proportional hazards model by incorporating a random covariate and unobservable random institution effect to respectively account for treatment-by-institution interaction and institutional variation in the baseline risk.

Consumption of dietary supplements by Chinese women during pregnancy and postpartum: A prospective cohort study.

The objectives of this study were to investigate usage patterns and factors associated with maternal dietary supplementation by Chinese women. A prospective cohort study of 695 mothers, who gave birth to a singleton baby, was conducted in Jiangyou, Sichuan Province of China. Information on dietary supplement use was collected from participants by personal interview at hospital discharge and followed up by telephone at 1, 3, and 6 months postpartum.

Consumption of Chinese herbal medicines during pregnancy and postpartum: A prospective cohort study in China.

Objective: to investigate usage patterns and factors associated with maternal consumption of Chinese herbal medicines in China.

Design: prospective cohort study. Information on the use of Chinese herbal medicines was collected from mothers by personal interview at hospital discharge and followed up by telephone at one, three and six months postpartum.

Traffic accidents involving fatigue driving and their extent of casualties.

The rapid progress of motorization has increased the number of traffic-related casualties. Although fatigue driving is a major cause of traffic accidents, the public remains not rather aware of its potential harmfulness. Fatigue driving has been termed as a "silent killer.

Effective time window in reducing pituitary adenoma size by gamma knife radiosurgery.

Objectives: Although the effectiveness of gamma knife radiosurgery (GKRS) in controlling the size of pituitary adenomas has been well demonstrated in many studies, the time period in which significant changes in tumor size occurs has been investigated in a limited fashion. It is important to determine the therapeutic window of GKRS in treating pituitary adenomas, i.e.

Analyzing fault and severity in pedestrian-motor vehicle accidents in China.

The number of pedestrian-motor vehicle accidents and pedestrian deaths in China surged in recent years. However, a large scale empirical research on pedestrian traffic crashes in China is lacking. In this study, we identify significant risk factors associated with fault and severity in pedestrian-motor vehicle accidents.

Improvement in institutional protocols leads to decreased mortality in patients with haemodynamically unstable pelvic fractures.

Background: The mortality rate in patients with haemodynamically unstable pelvic fractures is as high as 40-60%. In recent years, angioembolisation and pelvic packing have been introduced as part of a multimodality treatment for these patients. Protocol-driven management has been shown to improve outcomes.

Traffic violations in Guangdong Province of China: speeding and drunk driving.

The number of speeding- and drunk driving-related injuries in China surged in the years immediately preceding 2004 and then began to decline. However, the percent decrease in the number of speeding and drunk driving incidents (decrease by 22%) is not proportional to the corresponding percent decrease in number of automobile accident-related injuries (decrease by 47%) from the year 2004 to 2010 (Traffic Management Bureau, Ministry of Public Security, Annual Statistical Reports on Road Traffic Accidents). Earlier studies have established traffic violations as one of the major risks threatening road safety.

Risk factors associated with traffic violations and accident severity in China.

With the recent economic boom in China, vehicle volume and the number of traffic accident fatalities have become the highest in the world. Meanwhile, traffic accidents have become the leading cause of death in China. Systematically analyzing road safety data from different perspectives and applying empirical methods/implementing proper measures to reduce the fatality rate will be an urgent and challenging task for China in the coming years.

Trauma survival prediction in Asian population: a modification of TRISS to improve accuracy.

Unlabelled: The probability of survival (PS) in blunt trauma as calculated by Trauma and Injury Severity Score (TRISS) has been an indispensable tool in trauma audit. The aim of this study is to explore the predictive performance of the latest updated TRISS model by investigating the Age variable recategorisations and application of local Injury Severity Score (ISS) and Revised Trauma Score (RTS) coefficients in a logistic model using a level I trauma centre database involving Asian population.

Methods: Prospectively and consecutively collected 5684 trauma patients' data over a 10-year period at a regional level I trauma centre were reviewed.

Robust REML estimation for k-component Poisson mixture with random effects: application to the epilepsy seizure count data and urinary tract infections data.

A robust version of residual maximum likelihood estimation for Poisson log-linear mixed model is developed, and the method is extended to k-component Poisson mixture with random effects. The method not only provides the robust estimators for the fixed effects and variance component parameters but also gives the robust prediction of random effects. Simulation results show that the proposed method is effective in limiting the impact of outliers under different data contamination schemes.

Quantitative assessment of cerebral hemodynamic parameters by QUASAR arterial spin labeling in Alzheimer's disease and cognitively normal Elderly adults at 3-tesla.

QUASAR arterial spin labeling (ASL) was used to investigate the role of vascular impairment in Alzheimer's disease (AD). We hypothesized that the hemodynamic parameters monitoring cerebrovascular integrity, i.e.

Mixture cure model with random effects for clustered interval-censored survival data.

The mixture cure model is an effective tool for analysis of survival data with a cure fraction. This approach integrates the logistic regression model for the proportion of cured subjects and the survival model (either the Cox proportional hazards or accelerated failure time model) for uncured subjects. Methods based on the mixture cure model have been extensively investigated in the literature for data with exact failure/censoring times.

How to analyze longitudinal multilevel physical activity data with many zeros?

Background: Physical activity (PA) is a modifiable lifestyle factor for many chronic diseases with established health benefits. PA outcomes are measured and assessed in many longitudinal studies, but their analyses often pose difficulties due to the presence of many zeros, extreme skewness, and lack of independence, which render standard regression methods inappropriate.

Methods: A two-part multilevel modeling approach is used to analyze the heterogeneous and correlated PA data.

A score test for assessing the cured proportion in the long-term survivor mixture model.

The long-term survivor mixture model is commonly applied to analyse survival data when some individuals may never experience the failure event of interest. A score test is presented to assess whether the cured proportion is significant to justify the long-term survivor mixture model. Sampling distribution and power of the test statistic are evaluated by simulation studies.

Multilevel mixture cure models with random effects.

This paper extends the multilevel survival model by allowing the existence of cured fraction in the model. Random effects induced by the multilevel clustering structure are specified in the linear predictors in both hazard function and cured probability parts. Adopting the generalized linear mixed model (GLMM) approach to formulate the problem, parameter estimation is achieved by maximizing a best linear unbiased prediction (BLUP) type log-likelihood at the initial step of estimation, and is then extended to obtain residual maximum likelihood (REML) estimators of the variance component.

A computer graphical user interface for survival mixture modelling of recurrent infections.

Recurrent infections data are commonly encountered in medical research, where the recurrent events are characterised by an acute phase followed by a stable phase after the index episode. Two-component survival mixture models, in both proportional hazards and accelerated failure time settings, are presented as a flexible method of analysing such data. To account for the inherent dependency of the recurrent observations, random effects are incorporated within the conditional hazard function, in the manner of generalised linear mixed models.

Long-term survivor model with bivariate random effects: applications to bone marrow transplant and carcinoma study data.

Cured patients (or the so-called long-term survivors) are increasingly being observed in clinical trial studies. As exemplified in two data sets, the bone marrow transplantation study for leukaemia patients and the multi-centre study for patients with carcinoma in the oropharynx, a considerable portion of the patients in these studies are deemed to be cured. With the presence of random hospital/centre effects, a long-term survivor model with bivariate random effects is proposed to analyse clustered survival data with a possible portion of cured patients.

Minimum Hellinger distance estimation for k-component poisson mixture with random effects.

The k-component Poisson regression mixture with random effects is an effective model in describing the heterogeneity for clustered count data arising from several latent subpopulations. However, the residual maximum likelihood estimation (REML) of regression coefficients and variance component parameters tend to be unstable and may result in misleading inferences in the presence of outliers or extreme contamination. In the literature, the minimum Hellinger distance (MHD) estimation has been investigated to obtain robust estimation for finite Poisson mixtures.

Maternity length of stay modelling by gamma mixture regression with random effects.

Maternity length of stay (LOS) is an important measure of hospital activity, but its empirical distribution is often positively skewed. A two-component gamma mixture regression model has been proposed to analyze the heterogeneous maternity LOS. The problem is that observations collected from the same hospital are often correlated, which can lead to spurious associations and misleading inferences.

Multilevel survival modelling of recurrent urinary tract infections.

A multilevel survival frailty model is presented for analyzing clustered and recurrent urinary tract infections among elderly women residing in aged-care institutions. At the subject level, serial dependence is expected between recurrent events recorded on the same individual. At the cluster level, correlations of observations within the same institution are present due to the inherent residential environment and hierarchical setting.

Assessing local influence in principal component analysis with application to haematology study data.

In many medical and health studies, high-dimensional data are often encountered. Principal component analysis (PCA) is a commonly used technique to reduce such data to a few components that includes most of the information provided by the original data. However, PCA is known to be very sensitive to some abnormal observations.

Under-nutrition affects time to recurrence of gastroenteritis among Aboriginal and non-Aboriginal children.

This study investigated whether under-nutrition affected time to hospitalization for recurrence of gastroenteritis in Australian children. Linked hospitalization records of all infants, born in 1995 and 1996 in Western Australia, who were admitted for gastroenteritis during their first year of life (n=1001), were retrieved. A survival frailty model was used for determining the factors influencing the recurrent times over the subsequent seven years.

A score test for overdispersion in zero-inflated poisson mixed regression model.

Count data with extra zeros are common in many medical applications. The zero-inflated Poisson (ZIP) regression model is useful to analyse such data. For hierarchical or correlated count data where the observations are either clustered or represent repeated outcomes from individual subjects, a class of ZIP mixed regression models may be appropriate.

Multiple-vehicle traffic accidents in Hong Kong.

'Multiple-vehicle traffic accident' refers to a crash between two or more moving objects. Unlike single-vehicle accidents, not all drivers involving in a multiple-vehicle accident are responsible for the occurrence of the event. Accordingly, variables such as road type, speed limit and number of vehicles involved in the accident are expected to play a much more important role in association with injury severity in multiple-vehicle accidents.