scholarly journals A hybrid approach for the stratified mark‐specific proportional hazards model with missing covariates and missing marks, with application to vaccine efficacy trials

2020 ◽  
Vol 69 (4) ◽  
pp. 791-814
Author(s):  
Yanqing Sun ◽  
Li Qi ◽  
Fei Heng ◽  
Peter B. Gilbert
Keyword(s):  
Vaccine Efficacy ◽  
Proportional Hazards ◽  
Proportional Hazards Model ◽  
Hybrid Approach ◽  
Missing Covariates ◽  
Efficacy Trials ◽  
Hazards Model

Wind turbine prognostics and maintenance management based on a hybrid approach of neural networks and a proportional hazards model

2017 ◽  
Vol 231 (2) ◽  
pp. 121-129 ◽  
Author(s):  
Peyman Mazidi ◽  
Lina Bertling Tjernberg ◽  
Miguel A Sanz Bobi
Keyword(s):  
Condition Monitoring ◽  
Wind Farm ◽  
Stress Condition ◽  
Proportional Hazards ◽  
Proportional Hazards Model ◽  
Hybrid Approach ◽  
Principal Component ◽  
Mathematical Form ◽  
Hazards Model ◽  
Normal Behavior

This paper proposes an approach for stress condition monitoring and maintenance assessment in wind turbines (WTs) through large amounts of collected data from the supervisory control and data acquisition (SCADA) system. The objectives of the proposed approach are to provide a stress condition model for health monitoring, to assess the WT’s maintenance strategies, and to provide recommendations on current maintenance schemes for future operations of the wind farm. At first, several statistical techniques, namely principal component analysis, Pearson, Spearman and Kendall correlations, mutual information, regressional ReliefF and decision trees are used and compared to assess the data for dimensionality reduction and parameter selection. Next, a normal behavior model is constructed by an artificial neural network which performs condition monitoring analysis. Then, a model based on the mathematical form of a proportional hazards model is developed where it represents the stress condition of the WT. Finally, those two models are jointly employed in order to analyze the overall performance of the WT over the study period. Several cases are analyzed with five-year SCADA data and maintenance information is utilized to develop and validate the proposed approach.

scholarly journals Vaccine Efficacy at a Point in Time

2021 ◽  
Author(s):  
Dean Follmann ◽  
Michael Fay
Keyword(s):  
Vaccine Efficacy ◽  
Proportional Hazards ◽  
Proportional Hazards Model ◽  
Vaccine Trial ◽  
Phase Iii ◽  
Cross Sectional ◽  
Transmission Potential ◽  
Viral Loads ◽  
Hazards Model ◽  
Vaccine Effect

AbstractVaccine trials are generally designed to assess efficacy on clinical disease. The vaccine effect on infection, while important both as a proxy for transmission and to describe a vaccine’s total effects, requires frequent longitudinal sampling to capture all infections. Such sampling may not always be feasible. A logistically easy approach is to collect a sample to test for infection at a regularly scheduled visit. Such point or cross-sectional sampling does not permit estimation of classic vaccine effiacy on infection, as long duration infections are sampled with higher probability. Building on work by Rinta-Kokko and others (2009) we evaluate proxies of the vaccine effect on transmission at a point in time; the vaccine efficacy on prevalent infection and on prevalent viral load, VEPI and VEPV L, respectively. Longer infections with higher viral loads should have more transmission potential and prevalent vaccine efficacy naturally captures this aspect. We apply a proportional hazards model for infection risk and show how these metrics can be estimated using longitudinal or cross-sectional sampling. We also introduce regression models for designs with multiple cross-sectional sampling. The methods are evaluated by simulation and a phase III vaccine trial with PCR cross-sectional sampling for subclinical infection is analyzed.

The Paradoxical Nature of The Proportional Hazards Model of Random Censorship

Statistics ◽  
1999 ◽  
Vol 31 (1) ◽  
pp. 67-78
Author(s):  
Sándor Csörgő ◽  
Julian J. Faraway
Keyword(s):  
Proportional Hazards ◽  
Proportional Hazards Model ◽  
Random Censorship ◽  
Hazards Model

HRA Model for Hypercholesterolemia Based on a Longitudinal Health Database

1998 ◽  
Vol 37 (02) ◽  
pp. 130-133
Author(s):  
T. Kishimoto ◽  
Y. Iida ◽  
K. Yoshida ◽  
M. Miyakawa ◽  
H. Sugimori ◽  
...  
Keyword(s):  
Total Cholesterol ◽  
Proportional Hazards ◽  
Proportional Hazards Model ◽  
Model Analysis ◽  
Serum Total Cholesterol ◽  
Hazards Model ◽  
The Mean ◽  
Health Database ◽  
Observation Period

AbstractTo evaluate the risk factors for hypercholesterolemia, we examined 4,371 subjects (3,207 males and 1,164 females) who received medical checkups more than twice at an AMHTS in Tokyo during the period from 1976 through 1991; and whose serum total cholesterol was under 250 mg/dl. The mean follow-up duration was 6.6 years. A self-registering questionnaire was administered at the time of the health checkup. The endpoint of this study was the onset of hypercholesterolemia when the level of serum total cholesterol was 250 mg/dl and over. We compared two prognosis groups (normal and hypercholesterol) in terms of age, examination findings and lifestyle. After assessing each variable, we employed Cox's proportional hazards model analysis to determine the factors related to the occurrence of hypercholesterolemia. According to proportional hazards model analysis, total cholesterol, triglyceride and smoking at the beginning, and hypertension during the observation period were selected in males; and total cholesterol at the beginning and age were selected in females to determine the factors related to the occurrence of hypercholesterolemia.

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