Page 302 - Contributed Paper Session (CPS) - Volume 2

CPS1871 Natividad J.M. et al.
Bayesian conditional autoregressive model for
mapping human immunodeficiency virus
incidence in the national capital region of the
Philippines
Natividad Jochelle Maan, Necesito Reinna Mae, Ocampo Shirlee, Leong
Robert Neil
Mathematics and Statistics Department, De La Salle University, Philippines

Abstract
Human Immunodeficiency Virus (HIV) infection continues to increase
in the Philippines and exhibit public health threat in contrast to the worldwide
trend that new HIV cases had gone down. New HIV cases in the Philippines
had surged by 3,147% from 2007 to 2017. The concentration of such increase
of HIV cases is in the National Capital Region (NCR) composed of sixteen cities
and 1 municipality which are considered as spatial units in this study. The aim
of this study is to provide a Bayesian spatial Conditional Autoregressive (CAR)
model that gives shrinkage and spatial smoothing of the raw relative risk
estimates of HIV in NCR. Using Moran’s I, results showed that sexually active
male population of NCR exhibits significant spatial autocorrelation. It was
observed that percentage of sexually active male individuals (15-85 years of
age) is found to be correlated to the incidence of HIV in NCR. Bayesian CAR
model that takes spatial autocorrelation into account was then used. In line
with this, Poisson-Gamma model with covariate was also used, together with
the Bayesian CAR, to identify the best fitted model for the estimated HIV
relative risk. Results revealed that Bayesian CAR was the best model as it
involves spatial autocorrelation and has the lowest value of DIC compared to
the Poisson-Gamma model. It was found out that in Bayesian CAR, eight areas
in NCR have high relative risk estimates namely Mandaluyong, Makati, Manila,
Marikina, Pasay, Pasig, Pateros, and San Juan. It would be best for health public
officials to provide health programs and to allocate funds in the said areas to
reduce the incidence of HIV cases.

Keywords
HIV relative risk, Bayesian CAR mapping; spatial autocorrelation; Poisson-
Gamma model; Moran’s I

1. Introduction
The Human Immunodeficiency Virus (HIV) that slowly attacks the immune
system which serves as defense against illness has become a public threat to
people. Acquired Immune Deficiency Syndrome (AIDS) is a syndrome caused
by HIV and such illness alters the immune system, making people much more
vulnerable to infections and diseases. This susceptibility worsens as the

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