Mahdi Alimohammadi - Academia.edu (original) (raw)
Papers by Mahdi Alimohammadi
Ricerche Di Matematica, Oct 12, 2022
Probability in the Engineering and Informational Sciences
Let$V_{(r,n,\tilde {m}_n,k)}^{(p)}$and$W_{(r,n,\tilde {m}_n,k)}^{(p)}$be the$p$-spacings of gener... more Let$V_{(r,n,\tilde {m}_n,k)}^{(p)}$and$W_{(r,n,\tilde {m}_n,k)}^{(p)}$be the$p$-spacings of generalized order statistics based on absolutely continuous distribution functions$F$and$G$, respectively. Imposing some conditions on$F$and$G$and assuming that$m_1=\cdots =m_{n-1}$, Hu and Zhuang (2006. Stochastic orderings betweenp-spacings of generalized order statistics from two samples.Probability in the Engineering and Informational Sciences20: 475) established$V_{(r,n,\tilde {m}_n,k)}^{(p)} \leq _{{\rm hr}} W_{(r,n,\tilde {m}_n,k)}^{(p)}$for$p=1$and left the case$p\geq 2$as an open problem. In this article, we not only resolve it but also give the result for unequal$m_i$'s. It is worth mentioning that this problem has not been proved even for ordinary order statistics so far.
Communications in Statistics - Theory and Methods, 2020
In this article, we first study the likelihood ratio ordering of generalized order statistics (GO... more In this article, we first study the likelihood ratio ordering of generalized order statistics (GOS) in both one-sample and two-sample problems. Then, we establish the transmission of the increasing hazard rate and decreasing reversed hazard rate aging properties of GOS. To do this, we extend Karlin's basic composition theorem for the functions of three variables. Then, we settle certain open problems in this regard by providing some counterexamples. We further investigate similar transmission cases which have not been addressed in the literature so far.
Probability in the Engineering and Informational Sciences, 2021
Due to the importance of generalized order statistics (GOS) in many branches of Statistics, a wid... more Due to the importance of generalized order statistics (GOS) in many branches of Statistics, a wide interest has been shown in investigating stochastic comparisons of GOS. In this article, we study the likelihood ratio ordering of ppp -spacings of GOS, establishing some flexible and applicable results. We also settle certain unresolved related problems by providing some useful lemmas. Since we do not impose restrictions on the model parameters (as previous studies did), our findings yield new results for comparison of various useful models of ordered random variables including order statistics, sequential order statistics, kkk -record values, Pfeifer's record values, and progressive Type-II censored order statistics with arbitrary censoring plans. Some results on preservation of logconvexity properties among spacings are provided as well.
Avicenna Journal of Neuro Psycho Physiology, 2018
In today's highly competitive world, organizations are constantly searching for new methods to im... more In today's highly competitive world, organizations are constantly searching for new methods to improve the performance of their staff. Objectives: The primary purpose of this research was to determine the effectiveness of group counseling based on motivational interviewing on employees' organizational citizenship behavior. Materials and Methods: The research method was a pre-test-post-test quasi-experimental design with a control group. The study population comprised all employees of Hadid Sazeh Pishro industrial group, who were working in 2018. To complete the questionnaire, all staff completed the organizational citizenship behavior questionnaire. Then, among those who obtained a lower score than others, 24 subjects were selected and randomly divided into experimental and control groups. Next, group counseling based on motivational interviews was held for the experimental group in 18 sessions, two hours a week, for two sessions. During this period, the control group did not receive any intervention. After completing the counseling, both groups were taken the post-test to measure the effect of the intervention. Two months after the post-test, the groups were reevaluated to assess the impact of intervention during follow-up. The obtained data were analyzed with 1-way multivariate and covariance analysis in SPSS V. 22. Results: Findings of the present study indicated that group counseling based on motivational interviewing had a positive impact on employees' organizational citizenship behavior (P<0.01) so that the mean scores of the staff in the experimental group in the post-test and follow-up were significantly higher compared with the control group. Conclusion: In this research, the effect of group-based motivational interviewing counseling on the promotion of employee's organizational citizenship behavior was confirmed, and this fact can help managers of different organizations to prepare and plan appropriately to improve the organizational citizenship behavior of their staff.
Statistics & Probability Letters, 2021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Naval Research Logistics (NRL), 2016
Additive convolution of unimodal and α‐unimodal random variables are known as an old classic prob... more Additive convolution of unimodal and α‐unimodal random variables are known as an old classic problem which has attracted the attention of many authors in theory and applied fields. Another type of convolution, called multiplicative convolution, is rather younger. In this article, we first focus on this newer concept and obtain several useful results in which the most important ones is that if fˆϕ is logconcave then so are Fˆϕ and F¯ˆϕ for some suitable increasing functions ϕ. This result contains ϕ(x)=x and ϕ(x)=ex as two more important special cases. Furthermore, one table including more applied distributions comparing logconcavity of f(x) and f(ex) and two comprehensive implications charts are provided. Then, these fundamental results are applied to aging properties, existence of moments and several kinds of ordered random variables. Multiplicative strong unimodality in the discrete case is also introduced and its properties are investigated. In the second part of the article, some refinements are made for additive convolutions. A remaining open problem is completed and a conjecture concerning convolution of discrete α‐unimodal distributions is settled. Then, we shall show that an existing result regarding convolution of symmetric discrete unimodal distributions is not correct and an easy alternative proof is presented. © 2016 Wiley Periodicals, Inc. Naval Research Logistics 63: 109–123, 2016
Statistics & Probability Letters, 2015
We show that discrete logconcavity of probability mass functions implies logconcavity of their di... more We show that discrete logconcavity of probability mass functions implies logconcavity of their distribution and survival functions. Applications are obtained and discrete strong unimodality of order statistics (OSs) is established. Illustrative examples are provided and finally discrete logconvexity of OSs is discussed.
Statistics & Probability Letters, 2011
Because of the importance of ordered random variables and, in general, generalized order statisti... more Because of the importance of ordered random variables and, in general, generalized order statistics (GOSs), in many branches of Statistics, a wide interest has been shown in investigating unimodality and strong unimodality of such random variables. Assuming certain restrictions on the model parameters and distributions, some authors have shown unimodality of GOSs. In this article, we shall provide some new
Probability in the Engineering and Informational Sciences, 2014
Unimodality and strong unimodality of the distribution of ascendingly ordered random variables ha... more Unimodality and strong unimodality of the distribution of ascendingly ordered random variables have been extensively studied in the literature, whereas these properties have not received much attention in the case of descendingly ordered random variates. In this paper, we show that log concavity of the reversed hazard rate implies that of the density function. Using this fundamental result, we establish some convexity properties of such random variables. To do this, we first provide a counterexample showing that a claim of Basak & Basak [7] about the lower record values is not valid. Then, we provide conditions under which unimodality properties of the distribution of lower k-record values would hold. Finally, some extensions to dual generalized order statistics in both univariate and multivariate cases are discussed.
Journal of Applied Sciences, 2007
Ricerche Di Matematica, Oct 12, 2022
Probability in the Engineering and Informational Sciences
Let$V_{(r,n,\tilde {m}_n,k)}^{(p)}$and$W_{(r,n,\tilde {m}_n,k)}^{(p)}$be the$p$-spacings of gener... more Let$V_{(r,n,\tilde {m}_n,k)}^{(p)}$and$W_{(r,n,\tilde {m}_n,k)}^{(p)}$be the$p$-spacings of generalized order statistics based on absolutely continuous distribution functions$F$and$G$, respectively. Imposing some conditions on$F$and$G$and assuming that$m_1=\cdots =m_{n-1}$, Hu and Zhuang (2006. Stochastic orderings betweenp-spacings of generalized order statistics from two samples.Probability in the Engineering and Informational Sciences20: 475) established$V_{(r,n,\tilde {m}_n,k)}^{(p)} \leq _{{\rm hr}} W_{(r,n,\tilde {m}_n,k)}^{(p)}$for$p=1$and left the case$p\geq 2$as an open problem. In this article, we not only resolve it but also give the result for unequal$m_i$'s. It is worth mentioning that this problem has not been proved even for ordinary order statistics so far.
Communications in Statistics - Theory and Methods, 2020
In this article, we first study the likelihood ratio ordering of generalized order statistics (GO... more In this article, we first study the likelihood ratio ordering of generalized order statistics (GOS) in both one-sample and two-sample problems. Then, we establish the transmission of the increasing hazard rate and decreasing reversed hazard rate aging properties of GOS. To do this, we extend Karlin's basic composition theorem for the functions of three variables. Then, we settle certain open problems in this regard by providing some counterexamples. We further investigate similar transmission cases which have not been addressed in the literature so far.
Probability in the Engineering and Informational Sciences, 2021
Due to the importance of generalized order statistics (GOS) in many branches of Statistics, a wid... more Due to the importance of generalized order statistics (GOS) in many branches of Statistics, a wide interest has been shown in investigating stochastic comparisons of GOS. In this article, we study the likelihood ratio ordering of ppp -spacings of GOS, establishing some flexible and applicable results. We also settle certain unresolved related problems by providing some useful lemmas. Since we do not impose restrictions on the model parameters (as previous studies did), our findings yield new results for comparison of various useful models of ordered random variables including order statistics, sequential order statistics, kkk -record values, Pfeifer's record values, and progressive Type-II censored order statistics with arbitrary censoring plans. Some results on preservation of logconvexity properties among spacings are provided as well.
Avicenna Journal of Neuro Psycho Physiology, 2018
In today's highly competitive world, organizations are constantly searching for new methods to im... more In today's highly competitive world, organizations are constantly searching for new methods to improve the performance of their staff. Objectives: The primary purpose of this research was to determine the effectiveness of group counseling based on motivational interviewing on employees' organizational citizenship behavior. Materials and Methods: The research method was a pre-test-post-test quasi-experimental design with a control group. The study population comprised all employees of Hadid Sazeh Pishro industrial group, who were working in 2018. To complete the questionnaire, all staff completed the organizational citizenship behavior questionnaire. Then, among those who obtained a lower score than others, 24 subjects were selected and randomly divided into experimental and control groups. Next, group counseling based on motivational interviews was held for the experimental group in 18 sessions, two hours a week, for two sessions. During this period, the control group did not receive any intervention. After completing the counseling, both groups were taken the post-test to measure the effect of the intervention. Two months after the post-test, the groups were reevaluated to assess the impact of intervention during follow-up. The obtained data were analyzed with 1-way multivariate and covariance analysis in SPSS V. 22. Results: Findings of the present study indicated that group counseling based on motivational interviewing had a positive impact on employees' organizational citizenship behavior (P<0.01) so that the mean scores of the staff in the experimental group in the post-test and follow-up were significantly higher compared with the control group. Conclusion: In this research, the effect of group-based motivational interviewing counseling on the promotion of employee's organizational citizenship behavior was confirmed, and this fact can help managers of different organizations to prepare and plan appropriately to improve the organizational citizenship behavior of their staff.
Statistics & Probability Letters, 2021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Naval Research Logistics (NRL), 2016
Additive convolution of unimodal and α‐unimodal random variables are known as an old classic prob... more Additive convolution of unimodal and α‐unimodal random variables are known as an old classic problem which has attracted the attention of many authors in theory and applied fields. Another type of convolution, called multiplicative convolution, is rather younger. In this article, we first focus on this newer concept and obtain several useful results in which the most important ones is that if fˆϕ is logconcave then so are Fˆϕ and F¯ˆϕ for some suitable increasing functions ϕ. This result contains ϕ(x)=x and ϕ(x)=ex as two more important special cases. Furthermore, one table including more applied distributions comparing logconcavity of f(x) and f(ex) and two comprehensive implications charts are provided. Then, these fundamental results are applied to aging properties, existence of moments and several kinds of ordered random variables. Multiplicative strong unimodality in the discrete case is also introduced and its properties are investigated. In the second part of the article, some refinements are made for additive convolutions. A remaining open problem is completed and a conjecture concerning convolution of discrete α‐unimodal distributions is settled. Then, we shall show that an existing result regarding convolution of symmetric discrete unimodal distributions is not correct and an easy alternative proof is presented. © 2016 Wiley Periodicals, Inc. Naval Research Logistics 63: 109–123, 2016
Statistics & Probability Letters, 2015
We show that discrete logconcavity of probability mass functions implies logconcavity of their di... more We show that discrete logconcavity of probability mass functions implies logconcavity of their distribution and survival functions. Applications are obtained and discrete strong unimodality of order statistics (OSs) is established. Illustrative examples are provided and finally discrete logconvexity of OSs is discussed.
Statistics & Probability Letters, 2011
Because of the importance of ordered random variables and, in general, generalized order statisti... more Because of the importance of ordered random variables and, in general, generalized order statistics (GOSs), in many branches of Statistics, a wide interest has been shown in investigating unimodality and strong unimodality of such random variables. Assuming certain restrictions on the model parameters and distributions, some authors have shown unimodality of GOSs. In this article, we shall provide some new
Probability in the Engineering and Informational Sciences, 2014
Unimodality and strong unimodality of the distribution of ascendingly ordered random variables ha... more Unimodality and strong unimodality of the distribution of ascendingly ordered random variables have been extensively studied in the literature, whereas these properties have not received much attention in the case of descendingly ordered random variates. In this paper, we show that log concavity of the reversed hazard rate implies that of the density function. Using this fundamental result, we establish some convexity properties of such random variables. To do this, we first provide a counterexample showing that a claim of Basak & Basak [7] about the lower record values is not valid. Then, we provide conditions under which unimodality properties of the distribution of lower k-record values would hold. Finally, some extensions to dual generalized order statistics in both univariate and multivariate cases are discussed.
Journal of Applied Sciences, 2007