Bayesian Estimation of Inequality and Poverty Indices in Case of Pareto Distribution Using Different Priors under LINEX Loss Function
Abstract
Bayesian estimators of Gini index and a Poverty measure are obtained in case of Pareto distribution under censored and complete setup. The said estimators are obtained using two noninformative priors, namely, uniform prior and Jeffreys’ prior, and one conjugate prior under the assumption of Linear Exponential (LINEX) loss function. Using simulation techniques, the relative efficiency of proposed estimators using different priors and loss functions is obtained. The performances of the proposed estimators have been compared on the basis of their simulated risks obtained under LINEX loss function.
1. Introduction
Thus, w0 is per capita annual income representing a minimum acceptable standard of living and P0 represents the proportion of population having income equal to or less than w0.
The estimation of Gini index (G) and Poverty measure (P0) and the associated inference using classical approach (parametric and nonparametric) is available in literature [5–8]. However, in the Bayesian setup, this has not evoked the interest of many researchers [9, 10]. In the present paper, our focus will be on the estimation of inequality and poverty indices in the Bayesian setup.
When the Bayesian method is used, the choice of appropriate prior distribution plays an important role, which may be categorized as informative, noninformative, and conjugate priors [11, 12]. In the present paper, three priors (two noninformative priors and one conjugate prior) are used to estimate shape parameter, Gini index, Average income, and Poverty measure. The two noninformative priors are Uniform prior and Jeffreys’ prior, while conjugate prior is chosen as Truncated Erlang distribution.
In Figures 1(a) and 1(b), values of L(θ) are plotted for the selected values of θ for b = 1 and b = −1. It is seen that, for b = 1, the function is quite asymmetric with a value exceeding the target being more serious than a value below the target. But, for b = −1, the function is also quite asymmetric with a value below the target value being more serious than a value exceeding the target.



This loss function has been considered by Zellner [17], Basu and Ebrahimi [19], and Afify [20] for different distributions.
In the present study, LINEX loss function is used for estimating the shape parameter, Gini index, Mean income, and a Poverty measure in the context of Pareto distribution using noninformative priors (Uniform prior and Jeffreys’ prior) and one conjugate prior (Truncated Erlang distribution) along with some assumptions regarding the sampled population. Bayesian approach with prior and posterior distributions along with sampling schemes in the context of Pareto distribution is given in Section 2. In Section 3, Bayesian estimators of shape parameter, Gini index, Mean income, and Poverty measure using different priors under the assumption of LINEX loss function are obtained. Finally, in Section 4, simulation is done to compare the efficiency of three different approaches using three priors and loss functions. The robustness of the hyperparameters is given in Section 4.1 through simulation study. Section 5 presents the conclusion of the study.
2. Preliminary about Sampling Scheme, Priors, and Posterior Densities
The Bayesian analysis of the Pareto distribution (2) is based on the following censored sampling scheme on personal income data. It is assumed that annual incomes of the n persons are under study but exact figures x1, x2, x3, … , xr are available only for those r individuals whose annual income does not exceed a prescribed annual income w0(>m), and for the remaining (n − r) individuals, the exact income figures are unknown but we do know that their annual income exceed the prescribed figure w0. Before the arrival of the sample data on personal incomes, n is predetermined but not r, which is a random. This censoring scheme used is referred as right censored sampling scheme.
Bayes estimators of Gini index and Average income will not be convergent in the interval [0,1/2] and [0,1], respectively, and the method will fail to work. Hence, this difficulty is removed by assuming δ > 1, to obtain different Bayes estimators.
The prior and posterior densities for noninformative priors (Uniform prior and Jeffreys’ prior) and conjugate prior are explained below.
(i) Uniform Prior. In practice, the informative priors are not always available; for such situations, the use of noninformative priors is recommended. One of the most widely used noninformative prior, due to Laplace [23], is a uniform prior. Therefore, the uniform prior has been assumed for the estimation of the shape parameter of the Pareto distribution.
(iii) Conjugate Prior. The conjugate prior was introduced by Raiffa and Schlaifer [26], where the prior and posterior distributions are from the same family, that is, the form of the posterior density has the same distributional form as the prior distribution. For the existence of Gini index and Mean income for the Pareto distribution, we must take into account a truncated prior distribution since the random variable α is defined in (δ, ∞), where the constant δ > 1 is assumed to be known.
3. Bayesian Estimation under Linear Exponential (LINEX) Loss Function Using Different Priors
3.1. Bayesian Estimators Using Uniform Prior
3.2. Bayesian Estimators Using Jeffreys’ Prior
3.3. Bayesian Estimators Using Conjugate Prior
Note: Case of Complete Sample. The Bayesian estimators for complete sample can be obtained using noninformative priors and conjugate prior by simply substituting r = n in the above estimators.
4. Simulation Study
In order to assess the statistical performance of these estimators of shape parameter, Gini index, Mean income, and Poverty measure using LINEX loss function, a simulation study is conduced. The estimated losses are computed using generated random samples from Pareto distribution of different sizes. These estimated losses are computed for sample sizes n = 20 (20) 100, α = 2.5 (1) 4.5, b = 1, δ = 1.5, and m = 450. The value of w0 = 859.6 should be taken from Poverty line given by the Government of India in 2009-10 for urban people. For the conjugate prior, the values of hyperparameter are taken as β = 0.5, l = 2; β = 2, and l = 2. The estimated losses of α, G, M, and P0 with LINEX loss function by using noninformative (Uniform prior and Jeffreys’ prior) and conjugate priors are tabulated in Tables 1, 2, 3, and 4, respectively.
n | α | Uniform prior | Jeffrey’s prior | Conjugate prior | |
---|---|---|---|---|---|
β = 0.5 l = 2 |
β = 2 l = 2 |
||||
20 | 2.5 | 0.200543 | 0.173893 | 0.112013 | 0.113299 |
3.5 | 0.423936 | 0.357678 | 0.281125 | 0.371823 | |
4.5 | 0.719781 | 0.456351 | 0.311154 | 0.710794 | |
40 | 2.5 | 0.110843 | 0.077269 | 0.050112 | 0.072872 |
3.5 | 0.207535 | 0.204212 | 0.145707 | 0.174398 | |
4.5 | 0.324085 | 0.228739 | 0.207738 | 0.344289 | |
60 | 2.5 | 0.065696 | 0.061891 | 0.058858 | 0.059336 |
3.5 | 0.135812 | 0.104322 | 0.102511 | 0.123564 | |
4.5 | 0.283127 | 0.211419 | 0.149228 | 0.224148 | |
80 | 2.5 | 0.048582 | 0.052477 | 0.044407 | 0.045243 |
3.5 | 0.094729 | 0.094126 | 0.081215 | 0.089861 | |
4.5 | 0.146575 | 0.140906 | 0.126948 | 0.163061 | |
100 | 2.5 | 0.047068 | 0.040324 | 0.034990 | 0.038336 |
3.5 | 0.072414 | 0.071366 | 0.065080 | 0.070502 | |
4.5 | 0.112283 | 0.104459 | 0.099383 | 0.131260 |
n | α | Uniform prior | Jeffrey’s prior | Conjugate prior | |
---|---|---|---|---|---|
β = 0.5 l = 2 |
β = 2 l = 2 |
||||
20 | 2.5 | 0.003944 | 0.0031157 | 0.002672 | 0.057322 |
3.5 | 0.000849 | 0.0007378 | 0.000700 | 0.016733 | |
4.5 | 0.000671 | 0.0005303 | 0.000463 | 0.009637 | |
40 | 2.5 | 0.001503 | 0.0011873 | 0.000963 | 0.008362 |
3.5 | 0.000642 | 0.0005590 | 0.000516 | 0.003782 | |
4.5 | 0.000314 | 0.0002975 | 0.000197 | 0.002782 | |
60 | 2.5 | 0.000811 | 0.0007397 | 0.000692 | 0.006373 |
3.5 | 0.000415 | 0.0003852 | 0.000319 | 0.001783 | |
4.5 | 0.000200 | 0.0001726 | 0.000159 | 0.000873 | |
80 | 2.5 | 0.000687 | 0.0006286 | 0.000586 | 0.002637 |
3.5 | 0.000298 | 0.0002746 | 0.000189 | 0.000978 | |
4.5 | 0.000141 | 0.0001403 | 0.000116 | 0.000512 | |
100 | 2.5 | 0.000611 | 0.0005395 | 0.000483 | 0.001032 |
3.5 | 0.000231 | 0.0002250 | 0.000102 | 0.000822 | |
4.5 | 0.000115 | 0.0001073 | 0.000083 | 0.000421 |
n | α | Uniform prior | Jeffrey’s prior | Conjugate prior | |
---|---|---|---|---|---|
β = 0.5 l = 2 |
β = 2 l = 2 |
||||
20 | 2.5 | 0.073957 | 0.0657402 | 0.026145 | 0.056465 |
3.5 | 0.061835 | 0.0558135 | 0.015994 | 0.046743 | |
4.5 | 0.056649 | 0.0418561 | 0.012289 | 0.035673 | |
40 | 2.5 | 0.073204 | 0.0555914 | 0.025888 | 0.043674 |
3.5 | 0.060616 | 0.0466542 | 0.016802 | 0.040301 | |
4.5 | 0.055089 | 0.0435518 | 0.013802 | 0.031533 | |
60 | 2.5 | 0.072393 | 0.0458580 | 0.026035 | 0.039373 |
3.5 | 0.059386 | 0.0376830 | 0.017845 | 0.036373 | |
4.5 | 0.053528 | 0.0352241 | 0.015377 | 0.025377 | |
80 | 2.5 | 0.071778 | 0.0360502 | 0.026361 | 0.030012 |
3.5 | 0.058222 | 0.0286558 | 0.018818 | 0.029733 | |
4.5 | 0.051894 | 0.0267040 | 0.016845 | 0.020345 | |
100 | 2.5 | 0.071070 | 0.0263228 | 0.020575 | 0.027973 |
3.5 | 0.057185 | 0.0196096 | 0.019812 | 0.028732 | |
4.5 | 0.030343 | 0.0183061 | 0.018161 | 0.019637 |
n | α | Uniform prior | Jeffrey’s prior | Conjugate prior | |
---|---|---|---|---|---|
β = 0.5 l = 2 |
β = 2 l = 2 |
||||
20 | 2.5 | 0.003918 | 0.0016639 | 0.0015042 | 0.0037360 |
3.5 | 0.007714 | 0.0012619 | 0.0011718 | 0.0033510 | |
4.5 | 0.006892 | 0.0006375 | 0.0006100 | 0.0033324 | |
40 | 2.5 | 0.003030 | 0.0012092 | 0.0011452 | 0.0013573 |
3.5 | 0.001033 | 0.0007198 | 0.0007159 | 0.0016299 | |
4.5 | 0.001099 | 0.0003325 | 0.0003235 | 0.0011149 | |
60 | 2.5 | 0.002237 | 0.0009517 | 0.0008915 | 0.0011249 |
3.5 | 0.001652 | 0.0004774 | 0.0004483 | 0.0008925 | |
4.5 | 0.001019 | 0.0002165 | 0.0002040 | 0.0005813 | |
80 | 2.5 | 0.001769 | 0.0007372 | 0.0007191 | 0.0009047 |
3.5 | 0.001163 | 0.0003889 | 0.0003795 | 0.0006315 | |
4.5 | 0.000659 | 0.0001677 | 0.0001622 | 0.0003924 | |
100 | 2.5 | 0.001009 | 0.0006512 | 0.0005704 | 0.0007186 |
3.5 | 0.000465 | 0.0002854 | 0.0002770 | 0.0004269 | |
4.5 | 0.000287 | 0.0001354 | 0.0001240 | 0.0002843 |
- (i)
Bayesian estimators with conjugate prior (hyperparameter β = 0.5, l = 2) perform better as compared to noninformative priors as it has smaller estimated loss for α, G, M, and P0;
- (ii)
in case of noninformative priors, Jeffreys’ prior has less estimated loss than uniform prior, which implies that Bayesian methods with Jeffreys’ prior are better;
- (iii)
a change in the value of β on higher side does result in an increase in the loss; the loss remains unaffected by the change in the value of l.
n | α | Uniform prior | Jeffrey’s prior | Conjugate prior | ||
---|---|---|---|---|---|---|
β = 0.5 l = 2 |
β = 2 l = 2 |
|||||
For α | 40 | 2.5 | 0.198417 | 0.188773 | 0.105229 | 0.149043 |
3.5 | 0.545553 | 0.315654 | 0.301779 | 0.303094 | ||
4.5 | 0.636095 | 0.546807 | 0.511984 | 0.662855 | ||
100 | 2.5 | 0.081056 | 0.080694 | 0.065290 | 0.072233 | |
3.5 | 0.178339 | 0.192881 | 0.138684 | 0.139510 | ||
4.5 | 0.261753 | 0.299142 | 0.231038 | 0.215135 | ||
For G | 40 | 2.5 | 0.002541 | 0.002135 | 0.001879 | 0.053437 |
3.5 | 0.001215 | 0.001071 | 0.001055 | 0.033683 | ||
4.5 | 0.000989 | 0.000629 | 0.000222 | 0.026677 | ||
100 | 2.5 | 0.001347 | 0.001311 | 0.001054 | 0.011318 | |
3.5 | 0.000604 | 0.000408 | 0.000407 | 0.006967 | ||
4.5 | 0.000228 | 0.000236 | 0.000165 | 0.005405 | ||
For M | 40 | 2.5 | 0.085215 | 0.075152 | 0.061571 | 0.097215 |
3.5 | 0.092519 | 0.085051 | 0.070570 | 0.102310 | ||
4.5 | 0.157210 | 0.115720 | 0.095721 | 0.105721 | ||
100 | 2.5 | 0.105721 | 0.097121 | 0.050712 | 0.098721 | |
3.5 | 0.097215 | 0.070125 | 0.033710 | 0.059713 | ||
4.5 | 0.080712 | 0.052325 | 0.092530 | 0.082173 | ||
For P0 | 40 | 2.5 | 0.003513 | 0.004420 | 0.003916 | 0.005192 |
3.5 | 0.001382 | 0.003596 | 0.002156 | 0.004921 | ||
4.5 | 0.001224 | 0.001993 | 0.001057 | 0.003051 | ||
100 | 2.5 | 0.001152 | 0.001907 | 0.001805 | 0.001982 | |
3.5 | 0.000538 | 0.000914 | 0.000705 | 0.001572 | ||
4.5 | 0.000260 | 0.000896 | 0.000679 | 0.000971 |
From Table 5 and its comparison with LINEX loss function (ref. Tables 1, 2, 3, and 4), it is observed that LINEX loss function gives smaller loss in comparison with SELF for noninformative priors and conjugate prior for small as well as large sample sizes. When sample size increases estimated loss decreases in all cases.
4.1. Choice of Hyperparameters
Sinha and Howlader [28] suggested that a Bayes estimate is robust with respect to its hyperparameter if it leads to a high (min/max) index of the estimate for the varying values of those hyperparameter. To check results, simulations are done by taking different values of hyperparameter and keeping α and n fixed (ref. Tables 6 and 7).
β | l | (Min/Max) | β | ||||
---|---|---|---|---|---|---|
1 | 2 | 3 | 4 | 5 | ||
0.5 | 0.21247 | 0.22623 | 0.24944 | 0.23980 | 0.24143 | 0.853 |
1 | 0.23816 | 0.25030 | 0.22015 | 0.25817 | 0.23342 | 0.852 |
1.5 | 0.20394 | 0.22034 | 0.21269 | 0.23569 | 0.22392 | 0.865 |
2 | 0.22687 | 0.24029 | 0.22722 | 0.26901 | 0.25348 | 0.843 |
2.5 | 0.21976 | 0.23529 | 0.25022 | 0.24789 | 0.26048 | 0.845 |
(Min/Max) | l | 0.856 | 0.880 | 0.850 | 0.879 | 0.859 |
β | l | (Min/Max) | β | ||||
---|---|---|---|---|---|---|
1 | 2 | 3 | 4 | 5 | ||
0.5 | 0.89102 | 0.89271 | 0.89536 | 0.89844 | 0.89987 | 0.998 |
1 | 0.88525 | 0.88800 | 0.89170 | 0.89269 | 0.89549 | 0.989 |
1.5 | 0.88163 | 0.88560 | 0.88582 | 0.88885 | 0.89141 | 0.989 |
2 | 0.87639 | 0.87720 | 0.88162 | 0.88555 | 0.88619 | 0.988 |
2.5 | 0.87005 | 0.87451 | 0.87786 | 0.87947 | 0.88246 | 0.985 |
(Min/Max) | l | 0.976 | 0.979 | 0.980 | 0.978 | 0.980 |
The ratio (min/max) in case of both Gini index and Poverty measure is close to 1 for different combinations of l and β indicating thereby the Bayes estimates are robust with respect to hyperparameters, which justifies the use of hyperparameters in simulation study.
5. Conclusion
The simulation study as carried out in Section 4 suggests that Bayesian estimators using conjugate prior (hyperparameter β = 0.5, l = 2) perform better than two noninformative priors (Uniform prior and Jeffreys’ prior) in general. It is also observed that LINEX loss function results in smaller loss than the SELF for both small and large samples irrespective of the choice of the priors taken for the Bayesian estimators. Hence, the combinations of conjugate prior and LINEX loss results in smaller loss than the choice of other two priors and squared error loss function. One can further infer that as sample size increases the expected loss function decreases for all cases.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgments
The authors are thankful to the anonymous referees and the editor for their valuable suggestions and comments.