https://rivista-statistica.unibo.it/issue/feed Statistica 2022-07-12T13:45:11+02:00 Simone Giannerini stat.journal@unibo.it Open Journal Systems <strong>STATISTICA – ISSN 1973-2201</strong> is a quarterly journal, founded by Paolo Fortunati. Statistica accepts original papers dealing with methodological and technical aspects of statistics and statistical analyses in the various scientific fields. It publishes also book reviews and announcements. Full texts are available since 2002. https://rivista-statistica.unibo.it/article/view/13609 Comparison Between the Exact Likelihood and Whittle Likelihood for Moving Average Processes 2022-01-17T12:38:13+01:00 Xiaofei Xu xu.xiaofei@aoni.waseda.jp Zhengze Li 96lzz@akane.waseda.jp Masanobu Taniguchi taniguchi@waseda.jp <p>For Gaussian stationary processes, the likelihood functions include the inverse and determinant of the covariance matrices, and Whittle likelihood is considered as a standard technique to avoid expensive matrix determinant and inversions under large sample size. In this paper, we investigate the difference between the exact likelihood and Whittle likelihood with finite sample size for moving average processes of order one. We elucidate the theoretical expressions of two likelihood functions and their expectations and evaluate the performance between exact likelihood and Whittle likelihood numerically. We find that the exact likelihood and Whittle likelihood perform similarly when the true value of parameter is close to zero, while the difference becomes large and Whittle estimator performs poorly when absolute value of parameter gets close to one. This is an important warning when we use the Whittle likelihood and estimator if the parameter of moving average process nears the boundary of parameter space.</p> 2022-07-12T00:00:00+02:00 Copyright (c) 2022 Statistica https://rivista-statistica.unibo.it/article/view/12293 On a Bivariate XGamma Distribution Derived from Copula 2021-06-10T23:38:37+02:00 Mohammed Abulebda lebda86stat@gmail.com Ashok Kumar Pathak ashokiitb09@gmail.com Arvind Pandey arvindmzu@gmail.com Shikhar Tyagi shikhar1093tyagi@gmail.com <p>In this paper, a new bivariate XGamma (BXG) distribution is presented using Farlie-Gumbel-Morgenstern (FGM) copula. We derive the expressions for conditional distribution, regression function and product moments for the BXG distribution. Concept of reliability and various measures of local dependence are also studied for the proposed model. Furthermore, estimation of the parameters of the BXG distribution is obtained through maximum likelihood estimation and inference function of margin estimation procedures. Finally, an application of the same is also demonstrated to a real data set.</p> 2022-07-12T00:00:00+02:00 Copyright (c) 2022 Statistica https://rivista-statistica.unibo.it/article/view/13354 A Note on Fibonacci Sequences of Random Variables 2022-01-09T13:21:45+01:00 Ismihan Bayramoğlu ismihan.bayramoglu@ieu.edu.tr <p>The aim of this paper is to introduce and investigate the newrandom sequence in the form{<em>X</em><sub>0</sub>, <em>X</em><sub>1</sub>, <em>X<sub>n</sub></em> = <em>X</em><sub><em>n</em>−2</sub> +<em>X</em><sub><em>n</em>−1</sub>, <em>n</em> = 2, 3, ..˙} , referred to as Fibonacci Sequence of Random Variables (FSRV). The initial random variables <em>X</em><sub>0</sub> and <em>X</em><sub>1</sub> are assumed to be absolutely continuous with joint probability density function (pdf) <em>f</em><sub><em>X</em>0,<em>X</em>1</sub> . The FSRV is completely determined by <em>X</em><sub>0</sub> and <em>X</em><sub>1</sub> and the members of Fibonacci sequence F ≡ {0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ...}. We examine the distributional and limit properties of the random sequence <em>X</em><sub>n</sub>, <em>n</em> = 0, 1, 2, ... .</p> 2022-07-12T00:00:00+02:00 Copyright (c) 2022 Statistica https://rivista-statistica.unibo.it/article/view/9557 A Note on Estimation of Stress-Strength Reliability under Generalized Uniform Distribution when Strength Stochastically Dominates Stress 2021-11-07T15:14:11+01:00 Manisha Pal manishapal2@gmail.com <p>In this note we find the UMVUE and a consistent estimator of the stress strength reliability of a system, whose strength stochastically dominates the stress. Strength of the system and the stress on it are assumed to be independently distributed, each having a generalized uniformdistribution. Simulation study has been carried out, and an application to real life data has also been cited.</p> 2022-07-12T00:00:00+02:00 Copyright (c) 2022 Statistica https://rivista-statistica.unibo.it/article/view/13650 Comments on Irshad et al. (2021) “The Zografos-Balakrishnan Lindley Distribution: Properties and Applications” 2021-12-29T11:26:19+01:00 Hamid Ghorbani hamidghorbani@kashanu.ac.ir Muhammed Rasheed Irshad irshadmr@cusat.ac.in <p>This paper corrects and updates Irshad et al. (2021) by some technical comments. The original paperwas inadvertently published with some errors, mainly the computational ones regarding the maximum likelihood (ML) estimate of the parameters of the fitted models which will be addressed and corrected in this paper. Furthermore, the standard errors of the ML estimates of different fitted models, as an important indicator of the accuracy of estimates and particularly are necessary for making the statistical inference for the population parameters, have been added.</p> 2022-07-12T00:00:00+02:00 Copyright (c) 2022 Statistica