Naijun Sha

Naijun Sha

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Research Focus & Metrics

Academic Career Length

16Years (2011-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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1 February 2011 in Statistical Science
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TSTerrance Savitsky
Terrance Savitsky
MVMarina Vannucci
Marina Vannucci
NSNaijun Sha
Naijun Sha
This paper presents a unified treatment of Gaussian process models that extends to data from the exponential dispersion family and to survival data. Our specific interest is in the analysis of data sets with predictors that have an a priori unknown form of possibly nonlinear associations to the response. The modeling approach we describe incorporates Gaussian processes in a generalized linear model framework to obtain a class of nonparametric regression models where the covariance matrix depends on the predictors. We consider, in particular, continuous, categorical and count responses. We also look into models that account for survival outcomes. We explore alternative covariance formulations for the Gaussian process prior and demonstrate the flexibility of the construction. Next, we focus on the important problem of selecting variables from the set of possible predictors and describe a general framework that employs mixture priors. We compare alternative MCMC strategies for posterior inference and achieve a computationally efficient and practical approach. We demonstrate performances on simulated and benchmark data sets.


27 March 2015 in IEEE Transactions on Reliability
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Journal Article
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RWRonghua Wang
Ronghua Wang
NSNaijun Sha
Naijun Sha
BGBeiqing Gu
Beiqing Gu
XXXiaoling Xu
Xiaoling Xu
We consider statistical inference for two fundamental hybrid systems based on masked data: series-parallel, and parallel-series. Under constant, and linear hazard functions for component life, we present the maximum likelihood, and interval estimation of parameters of interest. Simulation studies are performed to demonstrate the efficiency of the methods.

16 June 2019 in Stats
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NSNaijun Sha
Naijun Sha
BDBenard Owusu Dechi
Benard Owusu Dechi
In this paper, we propose a Bayesian model for the analysis of categorical data with an ordered outcome. The method provides a latent variable approach with an informative prior transformed from a Dirichlet distribution for the boundary parameters. A simulation study is carried out to assess the performance of the methods under various settings of the data structure. Our method produces predictive accuracy over the conventional classification procedures. Real data are analyzed to demonstrate the efficiency of the proposed method.

27 October 2014 in Advances in Statistics
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RWRonghua Wang
Ronghua Wang
NSNaijun Sha
Naijun Sha
BGBeiqing Gu
Beiqing Gu
XXXiaoling Xu
Xiaoling Xu
We consider the parameter inference for a two-parameter life distribution with bathtub-shaped or increasing failure rate function. We present the point and interval estimations for the parameter of interest based on type-II censored samples. Through intensive Monte-Carlo simulations, we assess the performance of the proposed estimation methods by a comparison of precision. Example applications are demonstrated for the efficiency of the methods.

12 December 2018 in Stats
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Journal Article
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NSNaijun Sha
Naijun Sha
As a result of the two-parameter Birnbaum–Saunders (BS) distribution being successful in modelling fatigue failure times, several extensions of this model have been explored from different aspects. In this article, we consider a progressive stress accelerated life testing for the BS model to introduce a generalized Birnbaum–Saunders (we call it Type-II GBS) distribution on the lifetime of products in the test. We outline some interesting properties of this highly flexible distribution, present the Fisher’s information in the maximum likelihood estimation method, and propose a new Bayesian approach for inference. Simulation studies are carried out to assess the performance of the methods under various settings of parameter values and sample sizes. Real data are analyzed for illustrative purposes to demonstrate the efficiency and accuracy of the proposed Bayesian method over the likelihood-based procedure.