85 research outputs found
Estimation of COVID-19 spread curves integrating global data and borrowing information
Currently, novel coronavirus disease 2019 (COVID-19) is a big threat to
global health. The rapid spread of the virus has created pandemic, and
countries all over the world are struggling with a surge in COVID-19 infected
cases. There are no drugs or other therapeutics approved by the US Food and
Drug Administration to prevent or treat COVID-19: information on the disease is
very limited and scattered even if it exists. This motivates the use of data
integration, combining data from diverse sources and eliciting useful
information with a unified view of them. In this paper, we propose a Bayesian
hierarchical model that integrates global data for real-time prediction of
infection trajectory for multiple countries. Because the proposed model takes
advantage of borrowing information across multiple countries, it outperforms an
existing individual country-based model. As fully Bayesian way has been
adopted, the model provides a powerful predictive tool endowed with uncertainty
quantification. Additionally, a joint variable selection technique has been
integrated into the proposed modeling scheme, which aimed to identify possible
country-level risk factors for severe disease due to COVID-19
Investigating international new product diffusion speed: A semiparametric approach
Global marketing managers are interested in understanding the speed of the
new product diffusion process and how the speed has changed in our ever more
technologically advanced and global marketplace. Understanding the process
allows firms to forecast the expected rate of return on their new products and
develop effective marketing strategies. The most recent major study on this
topic [Marketing Science 21 (2002) 97--114] investigated new product diffusions
in the United States. We expand upon that study in three important ways. (1)
Van den Bulte notes that a similar study is needed in the international
context, especially in developing countries. Our study covers four new product
diffusions across 31 developed and developing nations from 1980--2004. Our
sample accounts for about 80% of the global economic output and 60% of the
global population, allowing us to examine more general phenomena. (2) His model
contains the implicit assumption that the diffusion speed parameter is constant
throughout the diffusion life cycle of a product. Recognizing the likely
effects on the speed parameter of recent changes in the marketplace, we model
the parameter as a semiparametric function, allowing it the flexibility to
change over time. (3) We perform a variable selection to determine that the
number of internet users and the consumer price index are strongly associated
with the speed of diffusion.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS519 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Bayesian Semiparametric Multivariate Density Deconvolution
We consider the problem of multivariate density deconvolution when the
interest lies in estimating the distribution of a vector-valued random variable
but precise measurements of the variable of interest are not available,
observations being contaminated with additive measurement errors. The existing
sparse literature on the problem assumes the density of the measurement errors
to be completely known. We propose robust Bayesian semiparametric multivariate
deconvolution approaches when the measurement error density is not known but
replicated proxies are available for each unobserved value of the random
vector. Additionally, we allow the variability of the measurement errors to
depend on the associated unobserved value of the vector of interest through
unknown relationships which also automatically includes the case of
multivariate multiplicative measurement errors. Basic properties of finite
mixture models, multivariate normal kernels and exchangeable priors are
exploited in many novel ways to meet the modeling and computational challenges.
Theoretical results that show the flexibility of the proposed methods are
provided. We illustrate the efficiency of the proposed methods in recovering
the true density of interest through simulation experiments. The methodology is
applied to estimate the joint consumption pattern of different dietary
components from contaminated 24 hour recalls
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