Estimation of Gumbel Parameters under Ranked Set Sampling

Transcription

1 Joural of Moder Applied Statistical Methods Volume 13 Issue 2 Article Estimatio of Gumbel Parameters uder Raked Set Samplig Omar M. Yousef Al Balqa' Applied Uiversity, Zarqa, Jorda, abuyaza_o@yahoo.com Sameer A. Al-Subh Mutah Uiversity, Karak, Jorda, salsubh@yahoo.com Follow this ad additioal works at: Part of the Applied Statistics Commos, Social ad Behavioral Scieces Commos, ad the Statistical Theory Commos Recommeded Citatio Yousef, Omar M. ad Al-Subh, Sameer A. (2014) "Estimatio of Gumbel Parameters uder Raked Set Samplig," Joural of Moder Applied Statistical Methods: Vol. 13 : Iss. 2, Article. DOI: /masm/ Available at: This Regular Article is brought to you for free ad ope access by the Ope Access Jourals at DigitalCommos@WayeState. It has bee accepted for iclusio i Joural of Moder Applied Statistical Methods by a authorized editor of DigitalCommos@WayeState.

2 Joural of Moder Applied Statistical Methods November 2014, Vol. 13, No. 2, Copyright 2014 JMASM, Ic. ISSN Estimatio of Gumbel Parameters uder Raked Set Samplig Omar M. Yousef Al Balqa Applied Uiversity Zarqa, Jorda S. A. Al-Subh Mutah Uiversity Karak, Jorda Cosider the MLEs (maximum likelihood estimators) of the parameters of the Gumbel distributio usig SRS (simple radom sample) ad RSS (raked set sample) ad the MOMEs (method of momet estimators) ad REGs (regressio estimators) based o SRS. A compariso betwee these estimators usig bias ad MSE (mea square error) was performed usig simulatio. It appears that the MLE based o RSS ca be a robust competitor to the MLE based o SRS. Keywords: Raked set samplig; simple radom samplig, parameters, Gumbel distributio, maximum likelihood estimator, bias, mea square error, regressio estimator, method of momet estimator. Itroductio There are may areas of applicatio of the Gumbel distributio icludig evirometal scieces, system reliability, ad hydrology. I hydrology, for example, the Gumbel distributio may be used to represet the distributio of the miimum level of a river i a particular year based o miimum values for the past few years. It is useful for predictig the occurrece of extreme earthquakes, floods, ad other atural disasters. The potetial applicability of the Gumbel distributio to represet the distributio of miima relates to extreme value theory, which idicates that it is likely to be useful if the distributio of the uderlyig sample data is of the ormal or expoetial type. The problem of estimatio of the ukow parameters of the Gumbel distributio is cosidered by may authors uder simple radom samplig. Maciuas et al. (1979) cosidered the estimates of the parameters of the Gumbel distributio by the methods of probability weighted momets, momets, ad Omar M. Yousef is a lecturer i the Basic Scieces Departmet. him at abuyaza_o@yahoo.com. Sameer A. Al-Subh is a assistat professor i the Departmet of Mathematics ad Statistics. him at salsubh@yahoo.com. 432

3 YOUSEF & AL-SUBH maximum likelihood. They used both idepedet ad serially correlated Gumbel umbers to derive the results from Mote Carlo experimets. They foud the method of probability weighted momets estimator is more efficiet tha the estimators. Leese (1973), derived the MLE (maximum likelihood estimator) of Gumbel distributio parameters i case of cesored samples ad he gave expressios for their large-sample stadard errors. Fioretio ad Gabriele (1984), give some modificatios of the MLE the Gumbel distributio parameters to reduce the bias of the estimators. Phie (1987) estimated the parameters of the Gumbel distributio by momets, MLE, maximum etropy ad probability weighted momets. He derived the asymptotic variace-covariace matrix of the MLEs ad used simulatio to compare betwee the various estimators. He foud that the MLE is best i terms of the root MSE (mea square error). Corsii et al. (1995), discussed the MLE ad Cramer-Rao (CR) bouds for the locatio ad scale parameters of the Gumbel distributio. Mousa et al. (2002), foud the Bayesia estimatio for the two parameters of the Gumbel distributio based o record values. RSS as itroduced by McItyre (1952) is a igeious samplig techique for selectig a sample which is more iformative tha a SRS to estimate the populatio mea. He used of RSS techique to estimate the mea pasture ad forage yields. RSS techique is very useful whe visual rakig of populatio uits is less expesive tha their actual quatificatios. Therefore, selectig a sample based o RSS ca reduce the cost ad icrease the efficiecy of estimatio. The basic idea behid selectig a sample uder RSS ca be described as follows: Select m radom samples each of size m, usig a visual ispectio or ay cheap method to rak the uits withi each sample with respect to the variable of iterest. The select, for actual measuremet, the i th smallest uit from the i th sample, i = 1,, m. I this way, a total of m measured uits are obtaied, oe from each sample. The procedure could be repeated r times util a sample of = mr measuremets are obtaied. These mr measuremets form RSS. Takahasi ad Wakimoto (1968) gave the theoretical backgroud for RSS. They showed that the mea of a RSS is a ubiased estimator of the populatio mea with variace smaller tha that of the mea of a SRS. Dell ad Clutter (1972) showed that the RSS mea remais ubiased ad more efficiet tha the SRS mea for estimatig the populatio eve if rakig is ot perfect. A comprehesive survey about developmets i RSS ca be foud i Che (2000) ad Muttlak ad Al-Saleh (2000). Because there are may attractive applicatios of Gumbel distributio, it is of iterest to coduct a statistical iferece for the Gumbel distributio. The statistical iferece icludes the study of some properties of Gumbel distributio, 433

4 ESTIMATION OF GUMBEL PARAMETERS emphasizig o estimatio of Gumbel parameters. The estimatio of the locatio ad scale parameters, deoted as α ad β respectively, of the Gumbel distributio uder SRS ad RSS is studied. The Gumbel parameters were estimated by usig several methods of estimatio i both cases of SRS ad RSS such as maximum likelihood, momets ad regressio. Furthermore, the performace of these estimators is ivestigated ad compared through simulatio. Bias, mea square error (MSE) ad efficiecy of these estimators were used for compariso. Parameter Estimatio Usig SRS The cdf ad pdf of the radom variable X which has a Gumbel distributio with parameters α ad β are give respectively by x Fx ( ;, ) exp exp, 1 x x f( x;, ) exp exp, (1) (2) where α is the locatio parameter ad β is the scale parameter, β > 0, x ad α (, ). Let X1, X2,, X be a radom sample from X. The MLEs, MOMEs (method of momet estimators) ad REGs (regressio estimators) will be examied i case of both parameters are ukow based o X1, X2,, X. MLEs Let X1, X2,, X be a radom sample from (2). The log-likelihood fuctio is give by xi xi l(, ) log exp. i1 i1 (3) 434

5 YOUSEF & AL-SUBH After takig the derivatives with respect to α ad β equatig to 0, the MLEs are obtaied as ˆ ad ˆ log. (4) ˆ x x w z MLE, S i i MLE, S MLE, S i1 where x i 1 zi zi exp, z zi ad wi. ˆ mle, S i1 z MOMEs The mea ad variace for Gumbel distributio are give by ad. (5) 6 The momet estimators of the two parameters are ˆMOME, S 6 s ad ˆ ˆ MOME, S x MOME, S (6) where s, x are the sample stadard deviatio ad mea, respectively, ad γ = is Euler s costat. REGs x x Let y Fx ( ;, ) exp exp l y= exp x x l y= exp t=l -l y = t a x b 1 where a ad b. 435

6 ESTIMATION OF GUMBEL PARAMETERS The regressio estimators of the two parameters are ˆ 1, ad ˆ ˆ,, ˆ REG S REG S REG S t ax (7) aˆ x x t t i i i1 where aˆ. 2 i1 x i x Parameter Estimatio Uder RSS MLEs Let X(i:m), i = 1,, m ad = 1,, r deote the i th order statistics from the i th set of size m of the th cycle be the RSS data for X with sample size = mr. Usig (1) ad (2), the pdf of X(i:m) is give by (Arold et al.,1992) i-1 m-i 1 fi : m( X ) cf( X ) 1- F( X ) f ( X ), where c B( i, m -i 1), 1 X X f( X ) exp exp ad F X by X ( ) exp exp. r l(, ) f ( X ) m i1 1 r m i1 1 i: m i r m i i1 1 The the likelihood fuctio is give -1 m-i = c F( X ) 1- F( X ) f ( X ) mr -1 m-i c F( X ) 1- F( X ) f ( X ). 436

7 YOUSEF & AL-SUBH The log-likelihood fuctio is give by r L(, ) mr log c ( i 1)log F( X ) m 1 i1 r m r m ( m i)log(1 F( X )) log f ( X ). 1 i1 1 i1 (8) Takig the derivatives of (8) with respect to α ad β respectively, ad equatig the resultig quatities to zero. Because there is o explicit solutio for (8), the equatios eed to be solved umerically to fid ˆ ˆ MLE, R ad MLE, R. Ad-hoc Estimators These are the same as the estimators i (6) ad (7) with SRS replaced by RSS Estimator Compariso A compariso betwee all above estimators for both parameters of the Gumbel distributio was carried out uder SRS ad RSS usig simulatio. The package R has bee used to coduct the simulatio. The followig values of the parameters ad sample sizes have bee cosidered: α = 0.5, β = 1; α = 1, β = 0.5; α = 1, β = 1; α = 1, β = 2; α = 2, β = 1, = ad =. For each, a set (m;r) is decided such that = mr. The bias ad the MSE are computed for all the estimators uder cosideratio. The efficiecy betwee all estimators with respect to the MLE based o SRS are calculated where the efficiecy of the estimator is defied as where If ˆ ˆ 2 1 ˆ ˆ ˆ MSE( 1) eff ( 2, 1) MSE( ˆ ) 10,000 ˆ 1 2 ˆ 2t 2 MSE. 10, 000 eff, 1 the ˆ 2 is better tha ˆ 1. The bias of the estimators is reported i Tables 1 ad 3 ad the efficiecies of the estimators is reported i Tables 2 ad 4. t

8 ESTIMATION OF GUMBEL PARAMETERS Table 1. The bias ad MSE of estimators of α Bias MSE (α, b) =mr ˆ mle,s ˆ moe,s ˆ reg,s ˆ mle,r ˆ moe,r ˆ mle,s ˆ moe,s ˆ reg,s ˆ mle,r ˆ moe,r (1,1) (1,2) (2,1) (0.5,1) (1,0.5) m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r=

9 YOUSEF & AL-SUBH Table 2. The efficiecy of estimators of α (α, b) =mr ˆ mle,s ˆ moe,s ˆ reg,s ˆ mle,r ˆ moe,r (1,1) (1,2) (2,1) (0.5,1) (1,0.5) m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r=

10 ESTIMATION OF GUMBEL PARAMETERS Table 3. The bias ad MSE of estimators of β Bias MSE (α, b) =mr ˆ mle,s ˆ moe,s ˆ reg,s ˆ mle,r ˆ moe,r ˆ mle,s ˆ moe,s ˆ reg,s ˆ mle,r ˆ moe,r (1,1) (1,2) (2,1) (0.5,1) (1,0.5) m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r=

11 YOUSEF & AL-SUBH Table 4. The efficiecy of estimators of β (α, b) =mr ˆ mle,s ˆ moe,s ˆ reg,s ˆ mle,r ˆ moe,r (1,1) (1,2) (2,1) (0.5,1) (1,0.5) m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= m=3, r= m=4, r= m=2, r= m=3, r= m=4, r= From Tables 1 to 4, the followig coclusios are put forth i) I geeral, the bias is large for all estimators. Therefore, all the estimators are cosidered as biased estimators for α. ii) From Table 1, it ca be oticed that the REG uder SRS has the smallest bias as compared to the other estimators cosidered i most cases. I geeral, for all estimators of α uder RSS, the bias is less tha the case uder SRS. iii) For fixed α, the MSE of ˆ decreases as the sample size icreases. iv) It is oticed that from Table 2 that MLE uder RSS is the most efficiet tha the MLE based o SRS. 441

12 ESTIMATION OF GUMBEL PARAMETERS v) The efficiecy of the other estimators (MOMEs ad REGs based o SRS ad RSS) are ot cosistet, sometimes less oe ad other times greater tha 1. Similar remarks ca be oticed for the case of β. Coclusio Based o this study, it may be cocluded that all estimators are biased. Because the MLEs uder RSS are more efficiet tha the MLE uder SRS, RSS is recommeded i case orderig ca be doe visually or by a iexpesive method. The other estimators are ot recommeded because they are ot cosistet. Refereces Arold, B. C., Balakrisha, N., & Nagaraa, H. N. (1992). A First Course i Order Statistics. New York: Joh Wiley ad Sos. Che, Z. (2000). O raked-set sample quatiles ad their applicatios. Joural of Statistical Plaig ad Iferece, 83, Corsii, G., Gii, F., Greco, M. V., & Verrazzai, L. (1995). Cramer-Rao bouds ad estimatio of the parameters of the Gumbel distributio. Aerospace ad Electroic Systems, 31(3), Dell, D. R., & Clutter, J. L. (1972). Raked set samplig theory with order statistics backgroud. Biometrics, 28, Fioretio, M., & Gabriele, S. (1984). A correctio for the bias of maximum-likelihood estimators of Gumbel parameters. Joural of Hydrology, 73(1-2), Gumbel, E. J. (1958). Statistics of Extremes. New York: Columbia Uiversity Press. Leese, M. N. (1973). Use of cesored data i the estimatio of Gumbel distributio parameters for aual maximum flood series. Water Resources Research, 9(6), doi: /WR009i006p01534 Maciuas, J., Matalas, N. C., & Wallis, J. R. (1979). Probability weighted momets compared with some traditioal techiques i estimatig Gumbel Parameters ad quatiles. Water Resources Research, 15(5), doi: /WR015i005p

13 YOUSEF & AL-SUBH McItyre, G. A. (1952). A method of ubiased selective samplig usig raked sets. Australia Joural of Agricultural Research, 3, Mousa, M. A. M., Jahee, Z. F., & Ahmad, A. A. (2002). Bayesia Estimatio, Predictio ad Characterizatio for the Gumbel Model Based o Records. A Joural of Theoretical ad Applied Statistics, 36(1), Muttlak, H. A., & Al-Saleh, M. F Recet developmets i raked set samplig, Pakista Joural of Statistics, 16, Phie, H. N. (1987). A review of methods of parameter estimatio for the extreme value type-1 distributio. Joural of Hydrology, 90(3 4), Takahasi, K., & Wakitmoto, K. (1968). O ubiased estimates of the populatio mea based o the sample stratified by meas of orderig. Aals of the Istitute of Statistical Mathematics, 20,