Pub Date : 2016-12-27DOI: 10.6092/ISSN.1973-2201/6140
Nathan Bennett, Srikanth K. Iyer, S. Jammalamadaka
We are interested in estimating the distribution of lifetimes, also called survival times, subject to a general censoring scheme called ``middle censoring'' (see Jammalamadaka and Mangalam (2003)). Both the Cox proportional hazards (Cox PH) and accelerated failure time (AFT) models are considered since each model has a baseline distribution function that is modified by the presence of covariates. The key contribution presented is the estimation of the effect of the covariate as well as the baseline distribution function. We conclude with an application to a contingent valuation study.
{"title":"Semiparametric Models with Covariates for Lifetime Data under a General Censoring Scheme with an Application to Contingent Valuation","authors":"Nathan Bennett, Srikanth K. Iyer, S. Jammalamadaka","doi":"10.6092/ISSN.1973-2201/6140","DOIUrl":"https://doi.org/10.6092/ISSN.1973-2201/6140","url":null,"abstract":"We are interested in estimating the distribution of lifetimes, also called survival times, subject to a general censoring scheme called ``middle censoring'' (see Jammalamadaka and Mangalam (2003)). Both the Cox proportional hazards (Cox PH) and accelerated failure time (AFT) models are considered since each model has a baseline distribution function that is modified by the presence of covariates. The key contribution presented is the estimation of the effect of the covariate as well as the baseline distribution function. We conclude with an application to a contingent valuation study.","PeriodicalId":45117,"journal":{"name":"Statistica","volume":"99 1","pages":"327-339"},"PeriodicalIF":1.9,"publicationDate":"2016-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71251084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2016-12-27DOI: 10.6092/ISSN.1973-2201/6439
D. Marasini, P. Quatto, E. Ripamonti
In this paper we consider a controversy on the use and interpretation of p-values in applied research. In recent years several applied and theoretical journals have started to discuss on the appropriate use of p-values in research fields such as Psychology, Ecology, and Medicine. First, the notion of p-value has some intrinsic limitations, which have been already highlighted in the statistical literature, but are far from being recognized in applied research. Second, it has emerged the so-called practice of p-hacking, which consists in analyzing and re-analyzing data until obtaining a significant result in terms of a p-value less than 0.05. In the light of these problems, we review two alternative theoretical frameworks, given by the use of Bayes factor and a recent proposal that leads to evaluate statistical hypotheses in terms of a priori and a posteriori odds ratios.
{"title":"The use of p-values in applied research: Interpretation and new trends","authors":"D. Marasini, P. Quatto, E. Ripamonti","doi":"10.6092/ISSN.1973-2201/6439","DOIUrl":"https://doi.org/10.6092/ISSN.1973-2201/6439","url":null,"abstract":"In this paper we consider a controversy on the use and interpretation of p-values in applied research. In recent years several applied and theoretical journals have started to discuss on the appropriate use of p-values in research fields such as Psychology, Ecology, and Medicine. First, the notion of p-value has some intrinsic limitations, which have been already highlighted in the statistical literature, but are far from being recognized in applied research. Second, it has emerged the so-called practice of p-hacking, which consists in analyzing and re-analyzing data until obtaining a significant result in terms of a p-value less than 0.05. In the light of these problems, we review two alternative theoretical frameworks, given by the use of Bayes factor and a recent proposal that leads to evaluate statistical hypotheses in terms of a priori and a posteriori odds ratios.","PeriodicalId":45117,"journal":{"name":"Statistica","volume":"76 1","pages":"315-325"},"PeriodicalIF":1.9,"publicationDate":"2016-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71251391","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2016-12-27DOI: 10.6092/ISSN.1973-2201/6520
A. M. Fares, V. Gopal
A new probability distribution from the polynomial family has been proposed for modeling heavy-tailed data that are continuous on the whole real line. we have derived some general properties of this distribution and applied it on several data sets of U.S stock market daily returns. The introduced model is symmetric and leptokurtic, it outperforms the peer distributions used for the given data from perspective of information criteria suggesting a new potential candidate for modeling data exhibiting heavy tails.
{"title":"The generalized double Lomax distribution with applications","authors":"A. M. Fares, V. Gopal","doi":"10.6092/ISSN.1973-2201/6520","DOIUrl":"https://doi.org/10.6092/ISSN.1973-2201/6520","url":null,"abstract":"A new probability distribution from the polynomial family has been proposed for modeling heavy-tailed data that are continuous on the whole real line. we have derived some general properties of this distribution and applied it on several data sets of U.S stock market daily returns. The introduced model is symmetric and leptokurtic, it outperforms the peer distributions used for the given data from perspective of information criteria suggesting a new potential candidate for modeling data exhibiting heavy tails.","PeriodicalId":45117,"journal":{"name":"Statistica","volume":"76 1","pages":"341-352"},"PeriodicalIF":1.9,"publicationDate":"2016-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71251687","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2016-12-27DOI: 10.6092/ISSN.1973-2201/6622
M. Scagliarini, A. Belluzzi, E. Scaioli, C. Cardamone
In Crohn’s Disease it is extremely important to detect the presence of symptomless mucosal inflammation in such a way as to prevent the evolution of the disease. The aim of this study is to identify predictor variables for estimating the risk of the presence of mucosal inflammation. The results show that the estimated model provides a clear picture of the relationship among the selected predictors and the outcome of interest and has a very appreciable ability for identifying patients at high risk of symptomless but persistent inflammation.
{"title":"Probabilistic assessment of symptomless inflammation in Crohn's Disease patients","authors":"M. Scagliarini, A. Belluzzi, E. Scaioli, C. Cardamone","doi":"10.6092/ISSN.1973-2201/6622","DOIUrl":"https://doi.org/10.6092/ISSN.1973-2201/6622","url":null,"abstract":"In Crohn’s Disease it is extremely important to detect the presence of symptomless mucosal inflammation in such a way as to prevent the evolution of the disease. The aim of this study is to identify predictor variables for estimating the risk of the presence of mucosal inflammation. The results show that the estimated model provides a clear picture of the relationship among the selected predictors and the outcome of interest and has a very appreciable ability for identifying patients at high risk of symptomless but persistent inflammation.","PeriodicalId":45117,"journal":{"name":"Statistica","volume":"76 1","pages":"301-314"},"PeriodicalIF":1.9,"publicationDate":"2016-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71251244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2016-09-30DOI: 10.6092/ISSN.1973-2201/6194
H. A. Noughabi
In this article, we propose a new approach to testing exponentiality for Type-II censored samples. Our method converts the original observations into transformed data which follow from a special distribution. It is shown that the proposed tests do not depend on the scale parameter of the exponential distribution and hence the tests are exact. Power performance of the proposed tests is compared with the existing tests against various alternatives. The results are impressive and the proposed tests have higher power than the competing tests. Finally, two real data from reliability literature as illustrate examples are presented.
{"title":"Testing the Validity of the Exponential Model Based on Type II Censored Data Using Transformed Sample Data","authors":"H. A. Noughabi","doi":"10.6092/ISSN.1973-2201/6194","DOIUrl":"https://doi.org/10.6092/ISSN.1973-2201/6194","url":null,"abstract":"In this article, we propose a new approach to testing exponentiality for Type-II censored samples. Our method converts the original observations into transformed data which follow from a special distribution. It is shown that the proposed tests do not depend on the scale parameter of the exponential distribution and hence the tests are exact. Power performance of the proposed tests is compared with the existing tests against various alternatives. The results are impressive and the proposed tests have higher power than the competing tests. Finally, two real data from reliability literature as illustrate examples are presented.","PeriodicalId":45117,"journal":{"name":"Statistica","volume":"76 1","pages":"221-232"},"PeriodicalIF":1.9,"publicationDate":"2016-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71251160","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2016-09-30DOI: 10.6092/ISSN.1973-2201/6620
B. D. Finetti
As it has been already done for the Corrado Gini's works, STATISTICA has accepted the invitation of some researchers who asked to republish the English translation of some fundamental De Finetti's papers. These works were translated into English and published in the volume: Bruno De Finetti, Induction and Probability, Biblioteca di Statistica, eds. P. Monari, D. Cocchi, Clueb, Bologna, 1993. On the Probability Concept is one of the first fundamental philosophical papers in which we can find the essential basis of De Finetti's subjective approach to the Theory of probability.
正如已经为Corrado Gini的作品所做的那样，STATISTICA已经接受了一些研究人员的邀请，他们要求重新出版De Finetti的一些基本论文的英文翻译。这些作品被翻译成英文，并发表在卷:布鲁诺·德·菲内蒂，归纳和概率，Biblioteca di统计，编辑。P. Monari, D. Cocchi，俱乐部，博洛尼亚，1993年。《概率论》是德·菲内蒂对概率论的主观方法的本质依据的最早的哲学基础论文之一。
{"title":"On the Probabilty Concept","authors":"B. D. Finetti","doi":"10.6092/ISSN.1973-2201/6620","DOIUrl":"https://doi.org/10.6092/ISSN.1973-2201/6620","url":null,"abstract":"As it has been already done for the Corrado Gini's works, STATISTICA has accepted the invitation of some researchers who asked to republish the English translation of some fundamental De Finetti's papers. These works were translated into English and published in the volume: Bruno De Finetti, Induction and Probability, Biblioteca di Statistica, eds. P. Monari, D. Cocchi, Clueb, Bologna, 1993. On the Probability Concept is one of the first fundamental philosophical papers in which we can find the essential basis of De Finetti's subjective approach to the Theory of probability.","PeriodicalId":45117,"journal":{"name":"Statistica","volume":"76 1","pages":"207-219"},"PeriodicalIF":1.9,"publicationDate":"2016-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71251607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2016-09-30DOI: 10.6092/ISSN.1973-2201/6243
V. A. Sharon, V. Vaidyanathan
This article introduces step-stress accelerated life time model with Lindley lifetime under type-I censoring. The corresponding likelihood function is developed and parameter estimation by maximum likelihood approach is discussed. Also, parametric bootstrap confidence intervals are constructed for the unknown parameters. Simulation study is carried out to evaluate performance of the estimators of the proposed model.
{"title":"Analysis of simple step-stress accelerated life test data from Lindley distribution under type-I censoring","authors":"V. A. Sharon, V. Vaidyanathan","doi":"10.6092/ISSN.1973-2201/6243","DOIUrl":"https://doi.org/10.6092/ISSN.1973-2201/6243","url":null,"abstract":"This article introduces step-stress accelerated life time model with Lindley lifetime under type-I censoring. The corresponding likelihood function is developed and parameter estimation by maximum likelihood approach is discussed. Also, parametric bootstrap confidence intervals are constructed for the unknown parameters. Simulation study is carried out to evaluate performance of the estimators of the proposed model.","PeriodicalId":45117,"journal":{"name":"Statistica","volume":"76 1","pages":"233-248"},"PeriodicalIF":1.9,"publicationDate":"2016-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71250873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2016-09-30DOI: 10.6092/ISSN.1973-2201/6621
Jerin Paul, P. Y. Thomas
In this paper we derive Sharma-Mittal entropy of record values and analyse some of its important properties. We establish some bounds for the Sharma-Mittal entropy of record values. We generate a characterization result based on the properties of Sharma-Mittal entropy of record values for exponential distribution. We further establish some distribution free properties of Sharma-Mittal divergence information between distribution of a record value and the parent distribution. We extend the concept of Sharma-Mittal entropy to the concomitants of record values arising from a Farlie-Gumbel-Morgenstern (FGM) bivariate distribution. Also we consider residual Sharma-Mittal Entropy and used it to describe some properties of record values.
{"title":"Sharma-Mittal Entropy Properties on Record Values","authors":"Jerin Paul, P. Y. Thomas","doi":"10.6092/ISSN.1973-2201/6621","DOIUrl":"https://doi.org/10.6092/ISSN.1973-2201/6621","url":null,"abstract":"In this paper we derive Sharma-Mittal entropy of record values and analyse some of its important properties. We establish some bounds for the Sharma-Mittal entropy of record values. We generate a characterization result based on the properties of Sharma-Mittal entropy of record values for exponential distribution. We further establish some distribution free properties of Sharma-Mittal divergence information between distribution of a record value and the parent distribution. We extend the concept of Sharma-Mittal entropy to the concomitants of record values arising from a Farlie-Gumbel-Morgenstern (FGM) bivariate distribution. Also we consider residual Sharma-Mittal Entropy and used it to describe some properties of record values.","PeriodicalId":45117,"journal":{"name":"Statistica","volume":"76 1","pages":"273-287"},"PeriodicalIF":1.9,"publicationDate":"2016-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71251658","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2016-09-30DOI: 10.6092/ISSN.1973-2201/6317
C. Kumar, Subha R. Nair
Here we consider an extended version of the Kumaraswamy modified inverse Weibull distribution and investigate some of its theoretical properties through deriving expressions for cumulative distribution function, reliability function, hazard rate function, quantile function, characteristic function, raw moments, median, mode etc. Certain reliability measures of the distribution are obtained along with the distribution and moments of its order statistics. The maximum likelihood estimation of the parameters of the distribution is discussed and certain real life data applications are given for illustrating the usefulness of the model. Further, with the help of simulated data sets it is shown that the average bias and mean square errors of the maximum likelihood estimators are in decreasing order as the sample size increases.
{"title":"An extended version of Kumaraswamy inverse Weibull distribution and its properties","authors":"C. Kumar, Subha R. Nair","doi":"10.6092/ISSN.1973-2201/6317","DOIUrl":"https://doi.org/10.6092/ISSN.1973-2201/6317","url":null,"abstract":"Here we consider an extended version of the Kumaraswamy modified inverse Weibull distribution and investigate some of its theoretical properties through deriving expressions for cumulative distribution function, reliability function, hazard rate function, quantile function, characteristic function, raw moments, median, mode etc. Certain reliability measures of the distribution are obtained along with the distribution and moments of its order statistics. The maximum likelihood estimation of the parameters of the distribution is discussed and certain real life data applications are given for illustrating the usefulness of the model. Further, with the help of simulated data sets it is shown that the average bias and mean square errors of the maximum likelihood estimators are in decreasing order as the sample size increases.","PeriodicalId":45117,"journal":{"name":"Statistica","volume":"76 1","pages":"249-272"},"PeriodicalIF":1.9,"publicationDate":"2016-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71251571","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2016-06-30DOI: 10.6092/ISSN.1973-2201/6320
M. Scagliarini, Mariarosaria Apreda, Ulrich Wienand, G. Valpiani, Nicola Napoli
Exponentially weighted moving average (EWMA) control charts have been successfully used in recent years in several areas of healthcare. Most of these applications have concentrated on the problem of detecting shifts in the mean level of a process. The EWMA chart for monitoring the variability has received, in general, less attention than its counterpart for the mean, although equally important and, to the best of our knowledge, it has never been used in the healthcare framework. In this work, EWMA control charts were applied retrospectively for monitoring the mean and variability of a hospital organizational performance indicator. The aim was to determine whether EWMA control charts can be used as a comprehensive approach for assessing the steady-state behaviour of the process and for early detection of changes indicating either improvement or deterioration in the performance of healthcare organizations. The results showed that the EWMA control schemes generate easy-to-read data displays that reflect process performance allowing a continuous monitoring and prompt detection of changes in process performance. Currently, hospital managers are designing an operating room dashboard which also includes the EWMA control charts.
{"title":"Exponentially Weighted Moving Average Control Schemes for Assessing Hospital Organizational Performance","authors":"M. Scagliarini, Mariarosaria Apreda, Ulrich Wienand, G. Valpiani, Nicola Napoli","doi":"10.6092/ISSN.1973-2201/6320","DOIUrl":"https://doi.org/10.6092/ISSN.1973-2201/6320","url":null,"abstract":"Exponentially weighted moving average (EWMA) control charts have been successfully used in recent years in several areas of healthcare. Most of these applications have concentrated on the problem of detecting shifts in the mean level of a process. The EWMA chart for monitoring the variability has received, in general, less attention than its counterpart for the mean, although equally important and, to the best of our knowledge, it has never been used in the healthcare framework. In this work, EWMA control charts were applied retrospectively for monitoring the mean and variability of a hospital organizational performance indicator. The aim was to determine whether EWMA control charts can be used as a comprehensive approach for assessing the steady-state behaviour of the process and for early detection of changes indicating either improvement or deterioration in the performance of healthcare organizations. The results showed that the EWMA control schemes generate easy-to-read data displays that reflect process performance allowing a continuous monitoring and prompt detection of changes in process performance. Currently, hospital managers are designing an operating room dashboard which also includes the EWMA control charts.","PeriodicalId":45117,"journal":{"name":"Statistica","volume":"76 1","pages":"127-139"},"PeriodicalIF":1.9,"publicationDate":"2016-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71251220","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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