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Showing 31 results for Subject:

Mohammad Reza Alavi, Rahim Chinipardaz,
Volume 1, Issue 1 (9-2007)
Abstract

The classical analysis is based on random samples. However, in many situations the observations are recorded according to a nonnegative function of observations. In this case the mechanism of sampling is called weighted sampling. The usual statistical methods based on a weighted sample may be not valid and have to be adjusted. In this paper adjusted methods under some particular weight functions for normal distribution are studied and a new distribution called double normal distribution, is introduced as a weighted normal distribution.
Rahim Chinipardaz, Hoda Kamranfar,
Volume 3, Issue 1 (9-2009)
Abstract

This paper is concerned with the study of the effect of outliers in GARCH models. Four common outliers are considered: additive outliers, innovation outliers, level change and temporary change. Each of the outlier is embedded to a GARCH model and then the effectness of outliers in this model is studied. The residuals of the models have been investigated for both cases, the usual GARCH model and the GARCH model in the present of outliers.
Aref Khanjari Idenak, Mohammadreza Zadkarami, Alireza Daneshkhah,
Volume 5, Issue 2 (2-2012)
Abstract

In this paper a new compounding distribution with increasing, decreasing, bathtub shaped and unimodal-bathtub shaped hazard rate function. The new three-parameters distribution as a generalization of the exponential power distribution is proposed. Maximum likelihood estimation of the parameters, raw-moments, density function of the order statistics, survival function, hazard rate function, mean residual lifetime, reliability function and median are presented. Then the properties of this distribution are illustrated based on a real data set.

Khadijeh Mehri, Rahim Chinipardaz,
Volume 5, Issue 2 (2-2012)
Abstract

This article is concerned with the comparison between posterior probability and p-value in two-parameter exponential distribution when the location parameter is considered as extra (nuisance) parameter. It has been shown that for a fixed p-value the posterior probability is increases as the number of observations gets large value. It means that it may be different results between classical and Bayesian point of view. This irreconcilability between classical evidence and Bayesian evidence is remained if we compare the lower bound of posterior probability under a class of reasonable prior distributions.

Gholam Ali Parham, Parisa Masjedi,
Volume 7, Issue 2 (3-2014)
Abstract

One of the issues in reviewing the performance of a financial market is existence of long-term memory. Since for a financial time series, we may find this feature in the volatility. So reviewing in volatility has been considered by many economists. A common method for identification and modeling of long-term memory in the volatility is to use FIGARCH models. In this paper, we identify and model long-term memory in the data exchange rates volatility (EUR/IRR). According to the statistical properties of skewness, heavy tail and excess kurtosis of data, assuming normal residuals being rejected and therefore cannot identify model by using common methods. The data structure looks NIG distribution is a good choice for the distribution of residuals. Hence with this assumption, we again identify model. The results show a good selection for data is FIGARCH-NIG model.

Forough Hajibagheri, Abdolrahman Rasekh, Mohammad Reza Akhoond,
Volume 8, Issue 1 (9-2014)
Abstract

The instability of the least squares parameter estimates under collinearity, might also causes instability of the residuals. If so, a large residual from a least squares fit might not be indicative of an erratic data point, and conversely. In order to resolve the problem of collinearity in the regression model, biased estimators like the Liu estimator is suggested. In this paper, it is shown that when Liu mean shift regression is used to mitigate the effect of the collinearity, the influence of some observations can be drastically changed and also the appropriate statistic for testing outliers is derived. In order to illustrate the performance of the proposed method, a real example is presented.

Aref Khanjari Idenak, Mohammadreza Zadkarami, Alireza Daneshkhah,
Volume 8, Issue 2 (3-2015)
Abstract

In this paper a new compounding distribution with increasing, decreasing, bathtub shaped and unimodal hazard rate function is proposed. The new four-parameters distribution is a generalization of the complementary exponential power distribution. The raw-moments, density function of the order statistics, survival function, hazard rate function, quantiles, mean residual lifetime and reliability function are presented. The estimation of the new distribution in a special case Poisson complementary exponential power distribution is studied by the method of maximum likelihood and EM algorithm. Expression for asymptotic distribution for the maximum likelihood estimation of the parameters of the PCEP distribution are obtained and for determining the precision of the variance and covariance of the estimations, a simulation is used, Then experimental results are illustrated based on the real data set.

Ali Doostmoradi, Mohammadreza Zadkarami, Mohammadreza Akhoond, Aref Khanjari Idenak,
Volume 8, Issue 2 (3-2015)
Abstract

In this paper a new distribution function based on Weibull distribution is introduced. Then the characteristics of this new distribution are considered and a real data set is used to compare this distribution with some of the generalized Weibull distributions.
Zahra Yazari, Sayed Mohammad Reza Alavi,
Volume 8, Issue 2 (3-2015)
Abstract

The randomized response technique is a procedure for collecting the information on sensitive characteristics without exposing the identity of the respondent. Optional randomized response models are based on the basic premise that a question may be sensitive for one respondent but may not be sensitive for another. In this paper a three stage optional randomized response model is proposed and its properties are discussed using simulation with R package. The mean and sensitivity level of household's income of students of Shahid Chamran University are estimated using this model.

Sayed Mohammad Reza Alavi, Mahboobeh Tajadini,
Volume 9, Issue 2 (2-2016)
Abstract

In survey sampling, the respondents often do not state the actual response to the sensitive questions. Randomized response techniques have been designed to protect the privacy of responses. This paper focused on the randomized response technique for qualitative variables based on Simmons method. Using idea of repeating answer, the new repeated randomized response technique is introduced. Its efficiency is compared with the Simmons technique. Proportion of student cheating in Shahid Chamran University is estimated using the proposed technique.

Mina Godazi, Mohammadreza Akhoond, Abdolrahman Rasekh Rasekh,
Volume 10, Issue 1 (8-2016)
Abstract

One of the methods that in recent years has attracted the attention of many researchers for modeling multivariate mixed outcome data is using the copula function. In this paper a regression model for mixed survival and discrete outcome data based on copula function is proposed. Where the continuous variable was time and could has censored observations. For this task it is assumed that marginal distributions are known and a latent variable was used to transform discrete variable to continuous. Then by using a copula function, the joint distribution of two variables was constructed and finally the obtained model was used to model birth interval data in Ahwaz city in south-west of Iran.


Ali Doostmoradi, Mohammadreza Zadkarami, Aref Khanjari Idenak, Zahara Fereidooni,
Volume 10, Issue 1 (8-2016)
Abstract

In this paper we propose a new distribution based on Weibull distribution. This distribution has three parameters which displays increasing, decreasing, bathtub shaped, unimodal and increasing-decreasing-increasing failure rates. Then consider characteristics of this distribution and a real data set is used to compared proposed distribution whit some of the generalized Weibull distribution.


Mahtab Tarhani, Sayed Mohammad Reaz Alavi,
Volume 10, Issue 2 (2-2017)
Abstract

In weighted sampling as a generalization of random sampling, every observation, y, is recorded with probably proportional to a non-negative function of y. In this paper, the normal regression model is investigated under the weighted sampling for a common weight function. Parameters of the model are estimated for known and unknown weight parameters. Using simulation, efficiency of estimators is studied when they have not closed forms. As an application, the data of number of visited  patients by specialist doctors in Social Security Organization of Ahvaz in Iran (SSOAI) are analyzed.


Sayed Mohammad Reza Alavi, Safura Alibabaie, Rahim Chinipardaz,
Volume 11, Issue 2 (3-2018)
Abstract

The standard Beta distribution is a suitable distribution for modeling the data that include proportions. In many situations which the data of proportions include a considerable number of zeros and ones, the inflated beta distributions are more appropriate. When probabilities of recording such observations are proportional to a nonnegative weight function, the recorded observations distributed as a weighted inflated Beta. This article focuses on the size biased inflated Beta distribution as a special case of weighted inflated Beta distribution with the power weight function. Some properties of this distribution is studied and its parameters are estimated using maximum likelihood and method of moments approaches. The estimators are compared via a simulation study. Finally, the real mortality data set is fitted for this model.


Reza Zabihi Moghadam, Rahim Chinipardaz, Gholamali Parham,
Volume 12, Issue 1 (9-2018)
Abstract

In this paper a method has been given to detect the shocks in structural time series using Kalman filter algorithm. As the Kalman filter algorithm is used for state space forms which include ARMA models as an especial case, the suggested method can be used for more general time series than linear models. Five shocks; additive outlier, level change, seasonal change, periodic change and slope change have been reviewed with this method. The performance of suggested method has been shown via a simulation study. The marriage data set from England has been considered as a real data set to study.


Behzad Mansouri, Rahim Chinipardaz,
Volume 12, Issue 2 (3-2019)
Abstract

In this paper, using Band matrix, a method has been proposed to estimating the covariance matrix of the ARMA model and the likelihood function of the ARMA model with diagonal covariance matrix has been obtained and approximations for Kullback-Leibler and Chernoff criteria were presented. In addition, two rules for discriminating the ARMA models has been proposed. A simulation and real data sets are used to illustrate the performance of the proposed rules. Significant reduction of the calculations for large time series and low discrimination error rate are two characteristics of the proposed rules. In addition no need to normal assumption is showed in a theorem.


Mohammad Reza Yeganegi, Rahim Chinipardaz,
Volume 13, Issue 1 (9-2019)
Abstract

‎This paper is investigating the mixture autoregressive model with constant mixing weights in state space form and generalization to ARMA mixture model‎. ‎Using a sequential Monte Carlo method‎, ‎the forecasting‎, ‎filtering and smoothing distributions are approximated and parameters f the model is estimated via the EM algorithm‎. ‎The results show the dimension of parameter vector in state space representation reduces‎. ‎The results of the simulation study show that the proposed filtering algorithm has a steady state close to the real values of the state vector‎. ‎Moreover‎, ‎according to simulation results‎, ‎the mean vectors of filtering and smoothing distribution converges to state vector quickly‎.


Ghasem Rekabdar, Rahim Chinipardaz, Behzad Mansouri,
Volume 13, Issue 1 (9-2019)
Abstract

‎In this study‎, ‎the multi-parameter exponential family of distribution has been used to approximate the distribution of indefinite quadratic forms in normal random vectors‎. ‎Moments of quadratic forms can be obtained in any orders in terms of representation of the quadratic forms as weighted sum of non-central chi-square random variables‎. ‎By Stein's identity in exponential family‎, ‎we estimated parameters of probability density function‎. ‎The method handled in some examples and we indicated this method suitable for approximating the quadratic form distribution.

Vahid Tadayon, Abdolrahman Rasekh,
Volume 13, Issue 1 (9-2019)
Abstract

Uncertainty is an inherent characteristic of biological and geospatial data which is almost made by measurement error in the observed values of the quantity of interest. Ignoring measurement error can lead to biased estimates and inflated variances and so an inappropriate inference. In this paper, the Gaussian spatial model is fitted based on covariate measurement error. For this purpose, we adopt the Bayesian approach and utilize the Markov chain Monte Carlo algorithms and data augmentations to carry out calculations. The methodology is illustrated using simulated data.


Mozhgan Dehghani, Mohammad Reza Zadkarami, Mohammad Reza Akhoond,
Volume 13, Issue 1 (9-2019)
Abstract

In the last decade, Poisson regression has been used for modeling count response variables. Poisson regression is not a suitable choice when count data bears superfluity of zero numbers. In this article, two models zero-inflated Poisson regression and bivariate zero-inflated Poisson regression with random effect are used to modeling count responses with a superfluity of zero numbers. Usually, distribution of the random effect is considered normal, but we intend to employ more flexible skew-normal distribution for the distribution of the random effect. Finally, the purpose model is applied to data which as obtained from the Shahid Chamran University of Ahvaz concerning the number of failed courses and fail grade point average semesters. we used a simulation method to verify parameter estimations. 



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مجله علوم آماری – نشریه علمی پژوهشی انجمن آمار ایران Journal of Statistical Sciences

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