50 research outputs found
Normalized Power Prior Bayesian Analysis
The elicitation of power prior distributions is based on the availability of historical data, and is realized by raising the likelihood function of the historical data to a fractional power. However, an arbitrary positive constant before the like- lihood function of the historical data could change the inferential results when one uses the original power prior. This raises a question that which likelihood function should be used, one from raw data, or one from a su±cient-statistics. We propose a normalized power prior that can better utilize the power parameter in quantifying the heterogeneity between current and historical data. Furthermore, when the power parameter is random, the optimality of the normalized power priors is shown in the sense of maximizing Shannon's mutual information. Some comparisons between the original and the normalized power prior approaches are made and a water-quality monitoring data is used to show that the normalized power prior is more sensible.Bayesian analysis, historical data, normalized power prior, power prior, prior elicitation, Shannon's mutual information.
Objective Bayesian analysis for the generalized exponential distribution
In this paper, we consider objective Bayesian inference of the generalized
exponential distribution using the independence Jeffreys prior and validate the
propriety of the posterior distribution under a family of structured priors. We
propose an efficient sampling algorithm via the generalized ratio-of-uniforms
method to draw samples for making posterior inference. We carry out simulation
studies to assess the finite-sample performance of the proposed Bayesian
approach. Finally, a real-data application is provided for illustrative
purposes.Comment: 13 pages, 5 figures, 2 table
PPG-based Heart Rate Estimation with Efficient Sensor Sampling and Learning Models
Recent studies showed that Photoplethysmography (PPG) sensors embedded in
wearable devices can estimate heart rate (HR) with high accuracy. However,
despite of prior research efforts, applying PPG sensor based HR estimation to
embedded devices still faces challenges due to the energy-intensive
high-frequency PPG sampling and the resource-intensive machine-learning models.
In this work, we aim to explore HR estimation techniques that are more suitable
for lower-power and resource-constrained embedded devices. More specifically,
we seek to design techniques that could provide high-accuracy HR estimation
with low-frequency PPG sampling, small model size, and fast inference time.
First, we show that by combining signal processing and ML, it is possible to
reduce the PPG sampling frequency from 125 Hz to only 25 Hz while providing
higher HR estimation accuracy. This combination also helps to reduce the ML
model feature size, leading to smaller models. Additionally, we present a
comprehensive analysis on different ML models and feature sizes to compare
their accuracy, model size, and inference time. The models explored include
Decision Tree (DT), Random Forest (RF), K-nearest neighbor (KNN), Support
vector machines (SVM), and Multi-layer perceptron (MLP). Experiments were
conducted using both a widely-utilized dataset and our self-collected dataset.
The experimental results show that our method by combining signal processing
and ML had only 5% error for HR estimation using low-frequency PPG data.
Moreover, our analysis showed that DT models with 10 to 20 input features
usually have good accuracy, while are several magnitude smaller in model sizes
and faster in inference time
Relations of Change in Plasma Levels of LDLâC, NonâHDLâC and apoB With Risk Reduction From Statin Therapy: A MetaâAnalysis of Randomized Trials
Background: Identifying the best markers to judge the adequacy of lipidâlowering treatment is increasingly important for coronary heart disease (CHD) prevention given that several novel, potent lipidâlowering therapies are in development. Reductions in LDLâC, nonâHDLâC, or apoB can all be used but which most closely relates to benefit, as defined by the reduction in events on statin treatment, is not established. Methods and Results: We performed a randomâeffects frequentist and Bayesian metaâanalysis of 7 placeboâcontrolled statin trials in which LDLâC, nonâHDLâC, and apoB values were available at baseline and at 1âyear followâup. Summary level data for change in LDLâC, nonâHDLâC, and apoB were related to the relative risk reduction from statin therapy in each trial. In frequentist metaâanalyses, the mean CHD risk reduction (95% CI) per standard deviation decrease in each marker across these 7 trials were 20.1% (15.6%, 24.3%) for LDLâC; 20.0% (15.2%, 24.7%) for nonâHDLâC; and 24.4% (19.2%, 29.2%) for apoB. Compared within each trial, risk reduction per change in apoB averaged 21.6% (12.0%, 31.2%) greater than changes in LDLâC (P<0.001) and 24.3% (22.4%, 26.2%) greater than changes in nonâHDLâC (P<0.001). Similarly, in Bayesian metaâanalyses using various prior distributions, Bayes factors (BFs) favored reduction in apoB as more closely related to risk reduction from statins compared with LDLâC or nonâHDLâC (BFs ranging from 484 to 2380). Conclusions: Using both a frequentist and Bayesian approach, relative risk reduction across 7 major placeboâcontrolled statin trials was more closely related to reductions in apoB than to reductions in either nonâHDLâC or LDLâC
Noninformative priors in Bayesian analysis
The reference priors, introduced by Bernardo (1979) and as further developed in Berger and Bernardo (1989a,b,c), are studied in several situations. These include nonlinear regression, sequential problems, and the unbalanced variance components problem. For nonlinear regression problems, there is a long history of the difficulties (such as impropriety of the posterior) resulting from common noninformative priors. The new group-ordered reference priors of Berger and Bernardo (1990b) are derived and shown to overcome the difficulties. Bayesian inferences under these priors are compared to each other and also compared to frequentist inference using the MLE. The results indicate considerable success for the preferred reference prior. In sequential experiments, where a stopping time is used, the Jeffreys noninformative prior for a multidimensional parameter is obtained as well as the reference prior. These noninformative priors depend on the expected stopping time. It is demonstrated that the Jeffreys prior depends on the stopping time in an inappropriate fashion for a multiparameter problem, while the reference prior does not. Some results on the admissibility of the resulting generalized Bayes rules are also developed. Finally, reference priors for the unbalanced variance components problem are derived and studied with respect to risk performance
A Bayesian hierarchical approach to dual response surface modelling
In modern quality engineering, dual response surface methodology is a powerful tool to model an industrial process by using both the mean and the standard deviation of the measurements as the responses. The least squares method in regression is often used to estimate the coefficients in the mean and standard deviation models, and various decision criteria are proposed by researchers to find the optimal conditions. Based on the inherent hierarchical structure of the dual response problems, we propose a Bayesian hierarchical approach to model dual response surfaces. Such an approach is compared with two frequentist least squares methods by using two real data sets and simulated data.