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Α Nakagami Dağılımı Için Optimal Asimtotik Testler

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Α Nakagami Dağılımı Için Optimal Asimtotik Testler Süleyman Demirel Üniversitesi Süleyman Demirel University Fen Bilimleri Enstitüsü Dergisi Journal of Natural and Applied Sciences Cilt 22, Özel Sayı, 487-492, 2018 Volume 22, Special Issue, 487-492, 2018 DOI: 10.19113/sdufbed.32458 Optimal Asymptotic Tests for Nakagami Distribution Deniz OZONUR*1, Hatice Tül Kübra AKDUR1, Hülya BAYRAK1 1Gazi Üniversitesi, Fen Fakültesi, İstatistik Bölümü, 06500, Ankara (Alınış / Received: 27.02.2018, Kabul / Accepted: 14.08.2018, Online Yayınlanma / Published Online: 23.09.2018) Keywords Abstract: Nakagami distribution is often used to model positive valued data with Likelihood Ratio test, right skewness. The distribution includes some familiar distributions as special Score test, cases such as Rayleigh and Half-normal distributions. In real life applications, one C ( ) test, of the simpler model may be sufficient to describe data. The aim of this paper is to Rayleigh distribution, adapt tests of goodness of fit of the Rayleigh distribution against Nakagami Nakagami distribution distribution. In this study likelihood ratio, C and score tests are specifically ( ) obtained. These tests are then compared in terms of type I error and power of test by a Monte Carlo simulation study. Nakagami Dağılımı için Optimal Asimtotik Testler Anahtar Kelimeler Özet: Nakagami dağılımı sağa çarpık pozitif değerli verileri modellemek için Olabilirlik Oran testi, sıklıkla kullanılır. Bu dağılım Rayleigh ve Yarı-Normal dağılım gibi bazı bilinen Skor testi, dağılımları içerir. Gerçek hayat uygulamalarında daha basit modellerden biri veriyi testi, tanımlamak için yeterli olabilir. Bu çalışmanın amacı Rayleigh dağılımına karşı Rayleigh dağılımı, Nakagami dağılımına uyum iyiliği testlerini uyarlamaktır. Bu çalışmada özel olarak Nakagami dağılımı olabilirlik oran, ve skor testleri elde edilmiştir. Daha sonra bu testler I. tip hata ve testin gücü bakımından Monte Carlo simülasyon çalışmasıyla karşılaştırılmıştır. 1. Introduction show the usefullness of the Nakagami distribution to deal with high-frequency seismogram envelopes. Characterization of wireless channels plays an Ozonur et al. (9) analyze performance of the important role in designing a reliable wireless goodness of fit tests for Nakagami distribution. communication system. Fading is occured during transmittion of signals from transmitter to receiver. The probability density function of Nakagami In the literature there are many statistical distribution is distribution to determine behavior of fading of m m 2m − x2 signals such as Rician, Rayleigh, lognormal, Weibull f( x; m ,) = x21m− e , x 0 (1) distributions. Nakagami distribution is one of the ()m m most common distribution among these distributions and the distribution was proposed by Nakagami [1] where m 0.5 is the shape parameter and 0 is to model fading of radio signals. the scale parameter. Applications of Nakagami distribution have been The mean and variance of the distribution are given carried out in many scientific fields such as by following equations respectively: engineering, hydrology and medicine. For example, Sarkar et al. [2, 3] use the distribution to derivate unit 12 +(m 0.5) hydrographs for estimating runoff in hydrology. EX( ) = Shankar et al. [4] and Tsui et al. [5] apply the (mm) Nakagami distribution to model ultrasound data in medical imaging studies. Also, the statistical 2 1 +(m 0.5) characteristics of “Moving Pictures Expert Group” VX( ) = 1. − (MPEG) is modelled by Nakagami distribution [6]. m (m) Carcole and Sato [7] and Nakahara and Carcole [8] *Corresponding author: [email protected] 487 D. Ozonur et al. / Optimal Asymptotic Tests for Nakagami Distribution Nakagami distribution includes some not been taken into consideration for Nakagami distributions as special cases. For example, distribution. Goodness of fit problem of the Nakagami distribution becomes Rayleigh distribution is considered in the study due to distribution when m = 1 , and one-sided Gaussian pervasive usage in many scientific areas as distribution when m = 12. Nakagami probability mentioned above. In this context, the main focus of densities are plotted for different/various m and this study is to test goodness of fit of Rayleigh parameter combinations in Figure 1. distribution against Nakagami distribution. 2. Test Statistics In this section asymptotically optimal goodness of fit tests such as likelihood ratio, Neyman’s test and Rao’s score test are obtained to compare Rayleigh distribution against Nakagami distribution. 2.1. Likelihood Ratio Test XX,, is a random sample from a Nakagami 1 n C distribution with (probability) density function given in Equation (1) with the parameter vector T =(m,.) Our interest is to test Hm0 :1= against the alternative Hm1 :1 . The log-likelihood function under the model (1) is given by Figure 1. Nakagami densities for various parameter combinations. l( ; x) = n( log( 2 mm ) − log ( m) − m log( )) In real applications, a one-parameter distribution nn m 2 may be sufficient to analyze data avoiding +(2m − 1) log xii − x . (2) unnecessary complications. Aim of the study is to ii==11 adapt tests of goodness of fit of the Rayleigh distribution against Nakagami distribution. The likelihood ratio test (LR) for testing H 0 against Specifically we adapt likelihood ratio test, Neyman’s H 1 is given as follows: test and Rao’s score test in the study. Monte Carlo simulation study is conducted to compare these ˆˆ (3) LR=−2 l( ; X) l( 0 ; X ) tests in terms of empirical size and power and ( ) concluding remarks are given. T T ˆ ˆ ˆ ˆ ˆ where =(m, ) and 00=(m =1, ) are the test is developed by regressing the residuals of maximum likelihood estimators of under the full the score function for the parameters of interest on model and under the null hypothesis respectively. By the score function for the nuisance parameters. The solving the following equations nuisance parameters are then replaced by some n nn consistent estimates ( n is number of observations). 1 2 nlog( m) + n − n ( m) − n log + 2 log xii − x = 0 statistic reduces to the score statistic, when ii==11 maximum likelihood estimators of nuisance n 2 parameters, which are consistent, are used [10]. mx −nm i +=i=1 0 Many authors have shown that the or score test 2 is asymptotically equivalent to the likelihood ratio the maximum likelihood estimates of parameters test [11, 12]. or score tests have some under alternative hypothesis are obtained as advantages such as maintaining a preassigned level of n x 2 significance approximately [13], requiring estimates i 1++ 1 4A /3 of the parameters only under the null hypothesis. =ˆ i =1 and mˆ = where n 4A Also, the tests often are calculated easily [14]. n 2 x These tests are all asymptotically optimal. They i 2 n =−i =1 Axlog log(i ) . provide tests with good properties in large samples nni =1 [15]. Although there are various studies including these goodness of fit tests [16, 17], these tests have 488 D. Ozonur et al. / Optimal Asymptotic Tests for Nakagami Distribution Here the notation m is digamma function, i.e., ( ) is the asymptotic covariance matrix of S m ( ) −1 (mm) =log ( ) . The statistic LR asymptotically and that is the asymptotic covariance matrix m ( ) follows a chi-square distribution with one degree of of mˆ [11]. The Rao’s score statistic is as follows: freedom under the null hypothesis. 2 ˆ S m ( 0 ) 2.2. C (α) and Score Tests T = (4) S ˆ ( 0 ) Rao [10] introduced score test as an alternative to which has an asymptotic Chi-square distribution with likelihood ratio test. Neyman [18] proposed 1 degree of freedom. test as a generalization of Rao’s score test. The and score test statistics are based on score functions. Neyman’s statistic is given by Score function and information matrix are given 2 lX( ; ) SIIS− −1 respectively by S = and ( mm( 0) ( 0) ( 0) ( 0 )) ( ) (5) TC = . i ˆ C () ( 0 ) 2 lX( ; ) IE( ) =− . Score function can be If the parameter , under null hypothesis, is ij replaced by its moment estimate =ˆ 4x 2 , which partitioned as mm are consistent, the distribution of TC is also Sm ( ) asymptotically Chi-square distribution with 1 degree S ( ) = of freedom. On the other hand, if is replaced by its S ( ) n ˆ 2 maximum likelihood estimate =mlxn i , the i=1 where S and S represent the first m ( ) ( ) statistic becomes the score statistic. derivative of log-likelihood function with respect to the parameter m and respectively. Similarly, 3. Simulation Study information matrix is obtained as follows: In this section, we compare performance of the test II mm( ) m ( ) statistics TC ,TS , LR in terms of Type I errors and I( ) = , IIm () ( ) powers of tests by using statistical software R 3.4.1. where elemets of I( ) denote the minus expected Firstly, critical values of the goodness of fit tests are obtained by simulating 10000 samples of size n from value of the second derivatives of the log-likelihood Nakagami distribution with m = 1. Using critical with respect to parameters. We obtained elements of values, type I errors are calculated by generating information matrix as 5000 random samples from Nakagami distribution n with m = 1 for various combinations of levels, 2 lX( ; ) sample sizes and scale parameters. In the simulation I= − E = n ' m − n m , mm 2 ( ) study, we consider sample sizes n = 20,30,50 and m scale parameters =0.3, 0.5,1,1.5, 3, 5 . Type I errors 2lX( ; ) of test statistis are summarized in Table 1. On the IIEmm= = − = 0, other hand, we obtain powers of test statistics based m on 10000 replicated samples of size from Nakagami distribution with different and m parameters. 2 In power study we only consider nominal level 0.05. lX( ; ) 2 I = − E2 = nm , Powers of test statistics are given in Table 2-4. As seen in Table 1, type I errors of all the three tests where trigamma function '(m) is derivative of close to nominal levels irrespective of values of scale parameter and sample size.
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