We consider two approaches for bias evaluation and reduction in the proportional hazards model (PHM) proposed by Cox. The rst one is an analytical approach in which we derive the n ?1 bias term of the maximum partial likelihood estimator. The second approach consists of resampling methods, namely the jackknife and the bootstrap. We compare all methods through a comprehensive set of Monte Carlo ...

Truncated power basis expansions and penalized spline methods are demonstrated for estimating nonlinear exposure-response relationships in the Cox proportional hazards model. R code is provided for fitting models to get point and interval estimates. The method is illustrated using a simulated data set under a known exposure-response relationship and in a data application examining risk of carpa...

lowing 3 groups: any antibiotics; antibiotics for respiratory infections; and antibiotics for urinary tract or skin and soft tissue infections. Asthma diagnosis was defined as having both an asthma diagnosis and receipt of asthma medications. The association between antibiotic exposure and asthmawas investigatedwithmultivariateCox proportional hazard regression models, and a stratified proporti...

Compared to the proportional hazards model and accelerated failure time model, the accelerated hazards model has a unique property in its application, in that it can allow gradual effects of the treatment. However, its application is still very limited, partly due to the complexity of existing semiparametric estimation methods. We propose a new semiparametric estimation method based on the indu...

In survival analysis, proportional hazards model is the most commonly used and the Cox model is the most popular. These models are developed to facilitate statistical analysis frequently encountered in medical research or reliability studies. In analyzing real data sets, checking the validity of the model assumptions is a key component. However, the presence of complicated types of censoring su...

The electoral system adopted by Hungary in 1989 represents a monument to the potential for institutional design through bargaining to produce complex yet stable institutions. The key compromise reached during this bargaining process was the decision to use the mixed member system, electing a roughly even measure of representatives from both majoritarian single-member districts (SMDs) and from m...

OBJECTIVE Little is known about the temporal impact of the rapid scale-up of large antiretroviral therapy (ART) services on programme outcomes. We describe patient outcomes [mortality, loss-to-follow-up (LTFU) and retention] over time in a network of South African ART cohorts. DESIGN Cohort analysis utilizing routinely collected patient data. METHODS Analysis included adults initiating ART ...

" Economic models in Merger Analysis: The analysis of the ATT-DTV Merger before the FCC-Appendix C "

Researchers can rely either on retrospectively reported or on prospectively measured health changes to identify and quantify recent changes in respondents' health status. The two methods typically do not provide the same answers. We compare the validity of prospective versus retrospective measures of health changes by investigating their predictive power for subsequent mortality. Data from a co...

This study investigated whether social modeling of palatable food intake might partially be explained by the direct imitation of a peer reaching for snack food and further, assessed the role of the children's own weight status on their likelihood of imitation during the social interaction. Real-time observations during a 10-min play situation in which 68 participants (27.9% overweight) interact...