
Galarneau [33], Gibbons [34], Ahmad and Aslam
[6] and Newhouse and Oman [35].
The following expression generates the regressors
1
22,1
1
ij ij i p
x z z
,
,
(41)
where
is independent standard normal
pseudorandom numbers,
is the correlation
between two explanatory variables, and p is the
number of explanatory variables. This study
considers the values of ρ to be 0.8, 0.9, 0.95, and
0.99. Also, explanatory variables (p) will be taken
to be three (3) and seven (7), and sample sizes 50
and 100 for the simulation study. The response
variable is defined as:
ippi eXXXY
...
2211
(42)
where
is normally distributed with mean 0 and
variance
. We choose
such that
=1. The
chosen values of
are 3, 5, and 10, and the
replication for the study is 1000 times. The mean
square error is then obtained as:
iij
jiij
MSE
ˆˆ
1000
1
ˆ
1000
1
(43)
4.1 Simulation Result
From Table 1-4, the simulation results presented
show that the proposed estimator outperforms all
other estimators used in this study. The proposed
estimator,
, in this study performs best at the
two different sample sizes considered (n = 50 and
100), four sigma levels (
= 1, 3, 5, and 10), four
different levels of multicollinearity levels (
=
0.8. 0.9, 0.95 and 0.99) and the two different
number of parameters (p=3 and 7). It provides a
smaller MSE compared with other estimators in
the study when the number of parameters is three
and seven. The OLS estimator is the least
performed estimator, which is expected due to the
facts established in the literature. The following
observations were also deduced from the result:
i. An increase in the level of correlation
results in an increase in the MSE for
all the estimators.
ii. The MSE increases for each estimator
as the level of error variances
increases.
iii. An increase in the sample size, n,
decreases the MSE for all the
estimators.
5. Numerical Example
In this section, Portland cement data was used to
demonstrate the performance of the proposed
estimator. The Portland cement data was originally
adopted by Woods et al. [36] and was later
adopted by Li and Yang [37] and then by Ayinde
et al. [38]. The data set is widely known as the
Portland cement dataset. The regression model for
these data is defined as:
1 1 2 2 3 3 4 4ii
y X X X X
(44)
where
= heat evolved after 180 days of curing
measured in calories per gram of cement,
=
tricalcium aluminate,
= tricalcium silicate,
= tetra calcium aluminoferrite, and
=
-
dicalcium silicate. The variance inflation factors
(VIF) are VIF1 = 38.50, VIF2 = 254.42, VIF3 =
46.87, and VIF4 = 282.51. Eigenvalues of
matrix are λ1 = 44676.206, λ2 = 5965.422, λ3 =
809.952, and λ4 = 105.419, and the condition
number of
is approximately 424. The VIFs,
eigenvalues, and condition numbers indicate that
severe multicollinearity exists. The estimated
parameters and the MSE values of the estimators
are presented in Table 5.
From Table 5, the proposed estimator (MLKL)
performs the best among all other estimators
because it gives the smallest MSE value. The OLS
estimator did not perform well in the presence of
multicollinearity, as it has the highest MSE.
6. Conclusions
This paper proposed a new two-parameter
estimator to handle the multicollinearity problem
for the linear regression models. The proposed
estimator was theoretically compared with five
other existing estimators. A simulation study was
then conducted to compare the performance of the
proposed estimator and the five existing
estimators: the OLS, Liu estimator, Ridge
estimator, KL estimator, and Modified One-
Parameter Liu estimator. It is evident from the
theoretical comparison that the proposed estimator
performs best among the existing estimators
considered in this research work.
A simulation study also supports the theoretical
analysis as the proposed estimator performs best
among all the existing estimators used in the study.
A real-life dataset was also analyzed to bolster the
theoretical comparison and simulation study
results. The proposed estimator gives the best
EQUATIONS
DOI: 10.37394/232021.2023.3.10
Olasunkanmi James Oladapo, Janet Iyabo Idowu,
Abiola Timothy Owolabi, Kayode Ayinde