Research Article
An Improved Estimation for Heterogeneous Datasets with Lower
Detection Limits regarding Environmental Health
Navid Feroze ,
1
Ali Akgul,
2
Taghreed M. Jawa ,
3
Neveen Sayed-Ahmed,
3
and Rashid Ali
4
1
Department of Statistics, The University of Azad Jammu and Kashmir, Muzaffarabad, Pakistan
2
Department of Mathematics, Siirt University, Art and Science Faculty, 56100 Siirt, Turkey
3
Department of Mathematics, College of Science, Taif University, Taif 21944, Saudi Arabia
4
School of Mathematics and Statistics, Central South University, Changsha, 410083 Hunan, China
Correspondence should be addressed to Navid Feroze; navidferoz@gmail.com
Received 28 April 2022; Accepted 7 June 2022; Published 12 July 2022
Academic Editor: Sania Qureshi
Copyright © 2022 Navid Feroze et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Analysis of environmental data with lower detection limits (LDL) using mixture models has recently gained importance. However,
only a particular type of mixture models under classical estimation methods have been used in the literature. We have proposed
the Bayesian analysis for the said data using mixture models. In addition, an optimal mixture distribution to model such data has
been explored. The sensitivity of the proposed estimators with respect to LDL, model parameters, hyperparameters, mixing
weights, loss functions, sample size, and Bayesian estimation methods has also been proposed. The optimal number of
components for the mixture has also been explored. As a practical example, we analyzed two environmental datasets involving
LDL. We also compared the proposed estimators with existing estimators, based on different goodness of fit criteria. The
results under the proposed estimators were more convincing as compared to those using existing estimators.
1. Introduction
The environmental studies often encounter the exposure
measurements falling below the LDL. These nondetectable
observations are considered left censored observations [1,
2]. Hughes [3] discussed that the difficulty in modeling the
environmental concentration datasets arises when some of
the measurements are below the LDL. As the proportion of
censored observations may not be trivial, failure to adjust
the censoring in the analysis can produce seriously biased
results with inflated variances. The most convenient method
to adjust the censoring is to replace the censored observation
by the detection limit. However, statistical properties of such
methods are obscured. As an improvement, Paxton et al. [4]
proposed the iterative imputation technique to settle the
censoring issue, but this method did not consider the corre-
lated structure of the data and parametric estimates.
Some authors have proposed the standard statistical dis-
tributions to model the left censored datasets. For example,
Mitra and Kundu [5] used generalized exponential distribu-
tion, Bhaumik et al. [6] employed normal distribution, Leith
et al. [7] and Jin et al. [8] used log-normal distribution, and
Asgharzadeh et al. [9] considered Weibull model to model
the left censored data from different situations. However,
varying modeling capabilities of these models to model the
left censored data has been reported by Vizard et al. [10].
Further, Moulton and Halsey [11] raised several concerns
over using a standard statistical model to deal with such
data. They argued that these datasets may be highly skewed
to make most of the standard models inappropriate for anal-
ysis. Further, there may exist an additional subpopulation of
the observations falling below the detection limit making the
data heterogeneous or multimodal. Following these argu-
ments, Moulton and Halsey [11] suggested the use of
gamma mixture model (in their case) to model the left cen-
sored HIV RNA dataset. Taylor et al. [12] also emphasized
that in case of larger proportion of nondetectable observa-
tions, a suitable model for analysis should be explored. They
Hindawi
Computational and Mathematical Methods in Medicine
Volume 2022, Article ID 4414582, 15 pages
https://doi.org/10.1155/2022/4414582