Constantinos Petropoulos - Profile on Academia.edu (original) (raw)

Applied Statistics by Constantinos Petropoulos

Health & Research Journal

Background: Mild head injuries in children are associated with morbidity and family distress. Tho... more Background: Mild head injuries in children are associated with morbidity and family distress. Though they are common causes of emergency department visits, they have been studied less than other more severe types of head trauma. This study aims to contribute to the reduction of this gap. Method and Materials: The medical records of 381 children with mild head injuries were reviewed and analyzed. Identification of any associated risk factors has been attempted with regression analysis. Results: The age group of 6-8 years was the most affected (44.6%). There was male predominance. Incidence presented seasonal variation. Concussion diagnosis was set in one tenth of patients. Half of children were under adult supervision during the traumatic incident. Cranial radiography was routinely performed in almost all patients, and computed tomography in 1.8%. Neurosurgical consultation was requested in 8.1%. Pedestrians, bicycle-riders, and car-passengers were at most risk of suffering mild head...

Spanish Journal of Agricultural Research, 2016

Eggplant is a widely cultivated vegetable crop of great economic importance. Its long lasting his... more Eggplant is a widely cultivated vegetable crop of great economic importance. Its long lasting history of domestication, selection and breeding has led to the development of numerous cultivars with variable traits. In the present study, we assessed the diversity levels within and among eleven Greek and foreign cultivars, using 22 morphological descriptors and two different classes of molecular markers (retrotransposon microsatellite amplified polymorphism-REMAP markers and nuclear microsatellites). Our results, in accordance with other studies in the field showed: a) the limited levels of genetic polymorphism within the cultivars; b) the high morphological and genetic divergence existing among them as indicated by the genetic distance values calculated, which could be attributed to selection, inbreeding and bottleneck effects; and c) the lack of concordance among morphological descriptors and molecular markers. Despite these, our analysis showed that the utilization of combinations o...

Agronomy

Crop landraces are found in many inhabited islands of Greece. Due to the particularity of environ... more Crop landraces are found in many inhabited islands of Greece. Due to the particularity of environment and isolation from the mainland, Greek islands represent a natural laboratory for comparing the diversity of landraces from the islands with those of the Greek mainland. A collection of 36 Greek eggplant landraces and traditional cultivars from the mainland and the islands has been phenotypically and genetically characterized using 22 morphological descriptors and 5 SSR markers. The mineral composition (K, Mg, Cu, Fe, Mn, Zn) of fruits was also determined. The objectives of this study include the multi-level characterization of eggplant local landraces and the comparison of diversity among accessions from the Greek mainland and the islands. Characterization of eggplant landraces will contribute to the enhancement and prevention of genetic erosion in this local group and will provide a resource for future investigation and breeding. PCA analysis of morphological traits explained 45.4...

Assessing diversity among traditional Greek and foreign eggplant cultivars using molecular markers and morphometrical descriptors

Spanish Journal of Agricultural Research, 2016

Mathematical Statistics by Constantinos Petropoulos

Improved estimators for parameters of a Pareto distribution with a restricted scale

ABSTRACT We consider the problem of estimating the parameters of a Pareto distribution under a qu... more ABSTRACT We consider the problem of estimating the parameters of a Pareto distribution under a quadratic loss when the scale parameter is constrained. The integral expression of risk difference (IERD), the approach of Kubokawa (1994) [12], and the Brewster and Zidek’s (1974) [5] technique are used to obtain the improved estimators over the standard estimators. Some complete class results are also proved.

A Class of Improved Estimators for the Scale Parameter of a Mixture Model of Exponential Distribution with Unknown Location

Communications in Statistics - Theory and Methods, 2010

ABSTRACT Under Stein's loss, a class of improved estimators for the scale parameter of a ... more ABSTRACT Under Stein's loss, a class of improved estimators for the scale parameter of a mixture of exponential distribution with unknown location is constructed. The method is analogous to Maruyama's (199811. Maruyama , Y. ( 1998 ). Minimax estimators of a normal variance . Metrika 48 : 209 – 214 . [CrossRef], [Web of Science ®]View all references) construction for the variance of a normal distribution and also an extension of the result produced in Petropoulos and Kourouklis (200213. Petropoulos , C. , Kourouklis , S. ( 2002 ). A class of improved estimators for the scale parameter of an exponential distribution with unknown location . Commun. Statist. Theor. Meth. 31 : 325 – 335 . [Taylor & Francis Online], [Web of Science ®]View all references). Also, robustness properties are considered.

Journal of Statistical Planning and Inference, 2005

Estimation of the scale parameter in mixture models with unknown location is considered under Ste... more Estimation of the scale parameter in mixture models with unknown location is considered under Stein's loss. Under certain conditions, the inadmissibility of the "usual" estimator is established by exhibiting better estimators. In addition, robust improvements are found for a speciÿed submodel of the original model. The results are applied to mixtures of normal distributions and mixtures of exponential distributions. Improved estimators of the variance of a normal distribution are shown to be robust under any scale mixture of normals having variance greater than the variance of that normal distribution. In particular, Stein's (Ann. Inst. Statist. Math. 16 (1964) 155) and Brewster's and Zidek's (Ann. Statist. 2 (1974) 21) estimators obtained under the normal model are robust under the t model, for arbitrary degrees of freedom, and under the double-exponential model. Improved estimators for the variance of a t distribution with unknown and arbitrary degrees of freedom are also given. In addition, improved estimators for the scale parameter of the multivariate Lomax distribution (which arises as a certain mixture of exponential distributions) are derived and the robustness of Zidek's (Ann. Statist. 1 (1973) 264) and Brewster's (Ann. Statist. 2 (1974) 553) estimators of the scale parameter of an exponential distribution is established under a class of modiÿed Lomax distributions.

Estimation of the parameters of an exponential distribution under constrained location

Mathematical Methods of Statistics, 2014

ABSTRACT In this paper, the problem of estimating parameters of an exponential population is stud... more ABSTRACT In this paper, the problem of estimating parameters of an exponential population is studied under quadratic loss functions. The location parameter of the distribution is assumed to be bounded above by a known constant. Various classes of estimators are derived using integral expression of risk difference (IERD) method of Kubokawa (1994). Some complete class results are also established.

Metrika, 2004

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New classes of improved confidence intervals for the variance of a normal distribution

Metrika, 2012

Two new classes of improved confidence intervals for the variance of a normal distribution with u... more Two new classes of improved confidence intervals for the variance of a normal distribution with unknown mean are constructed. The first one is a class of smooth intervals. Within this class, a subclass of generalized Bayes intervals is found which contains, in particular, the Brewster and Zidek-type interval as a member. The intervals of the second class, though non-smooth, have a very simple and explicit functional form. The Stein-type interval is a member of this class and is shown to be empirical Bayes. The construction extends Maruyama’s (Metrika 48:209–214, 1998) point estimation technique to the interval estimation problem.

Estimating the shape parameter of a Pareto distribution under restrictions

Metrika, 2015

A Class of Improved Estimators for the Scale Parameter of an Exponential Distribution with Unknown Location

Communication in Statistics Theory and Methods, Sep 1, 2006

Sankhyā: The Indian Journal of Statistics, 2006

Estimation of a quantile in a mixture model of exponential distributions is considered. For quadr... more Estimation of a quantile in a mixture model of exponential distributions is considered. For quadratic loss and specified extreme quantiles, better estimators than the best affine equivariant procedure are established. In particular, improved estimators for a quantile of an Exponential-Inverse Gaussian distribution and the multivariate Lomax distribution with unknown location and scale parameters are derived.

Estimating an Exponential Scale Parameter Under Double Censoring

Communications in Mathematics and Statistics

Statistical Methodology, 2011

Improved point estimation and interval estimation Scale parameter of an exponential distribution ... more Improved point estimation and interval estimation Scale parameter of an exponential distribution a b s t r a c t

Estimating an Exponential Scale Parameter Under Double Censoring

Communications in Mathematics and Statistics

Improved estimators of the entropy in scale mixture of exponential distributions

Brazilian Journal of Probability and Statistics

Improved estimators for functions of scale parameters in mixture models

Journal of the Korean Statistical Society

Estimating the scale parameter of an exponential distribution under progressive type II censoring

Communications in Statistics - Theory and Methods

Componentwise estimation of ordered scale parameters of two exponential distributions under a general class of loss function

Statistics

Health & Research Journal

Spanish Journal of Agricultural Research, 2016

Agronomy

Assessing diversity among traditional Greek and foreign eggplant cultivars using molecular markers and morphometrical descriptors

Spanish Journal of Agricultural Research, 2016

Improved estimators for parameters of a Pareto distribution with a restricted scale

A Class of Improved Estimators for the Scale Parameter of a Mixture Model of Exponential Distribution with Unknown Location

Communications in Statistics - Theory and Methods, 2010

Journal of Statistical Planning and Inference, 2005

Estimation of the parameters of an exponential distribution under constrained location

Mathematical Methods of Statistics, 2014

Metrika, 2004

The user has requested enhancement of the downloaded file.

New classes of improved confidence intervals for the variance of a normal distribution

Metrika, 2012

Estimating the shape parameter of a Pareto distribution under restrictions

Metrika, 2015

A Class of Improved Estimators for the Scale Parameter of an Exponential Distribution with Unknown Location

Communication in Statistics Theory and Methods, Sep 1, 2006

Sankhyā: The Indian Journal of Statistics, 2006

Estimating an Exponential Scale Parameter Under Double Censoring

Communications in Mathematics and Statistics

Statistical Methodology, 2011

Estimating an Exponential Scale Parameter Under Double Censoring

Communications in Mathematics and Statistics

Improved estimators of the entropy in scale mixture of exponential distributions

Brazilian Journal of Probability and Statistics

Improved estimators for functions of scale parameters in mixture models

Journal of the Korean Statistical Society

Estimating the scale parameter of an exponential distribution under progressive type II censoring

Communications in Statistics - Theory and Methods

Componentwise estimation of ordered scale parameters of two exponential distributions under a general class of loss function

Statistics

Minimax estimators for the lower-bounded scale parameter of a location-scale family of distributions

Communications in Statistics - Theory and Methods, 2016

ABSTRACT This article is concerned with the minimax estimation of a scale parameter under the qua... more ABSTRACT This article is concerned with the minimax estimation of a scale parameter under the quadratic loss function where the family of densities is location-scale type. We obtain results for the case when the scale parameter is bounded below by a known constant. Implications for the estimation of a lower-bounded scale parameter of an exponential distribution are presented under unknown location. Furthermore, classes of improved minimax estimators are derived for the restricted parameter using the Integral Expression for Risk Difference (IERD) approach of Kubokawa (1994). These classes are shown to include some existing estimators from literature.

Estimation of the shape parameter of a Pareto distribution

Communications in Statistics - Theory and Methods, 2017

ABSTRACT We consider the problem of estimating the shape parameter of a Pareto distribution with ... more ABSTRACT We consider the problem of estimating the shape parameter of a Pareto distribution with unknown scale under an arbitrary strictly bowl-shaped loss function. Classes of estimators improving upon minimum risk equivariant estimator are derived by adopting Stein, Brown, and Kubokawa techniques. The classes of estimators are shown to include some known procedures such as Stein-type and Brewster and Zidek-type estimators from literature. We also provide risk plots of proposed estimators for illustration purpose.

Children

Background: Head trauma is one of the most common pediatric emergencies. While the psychological ... more Background: Head trauma is one of the most common pediatric emergencies. While the psychological effects of severe head injuries are well studied, the psychological consequences of mild head injuries often go overlooked. Head injuries with a Glasgow Coma Scale score of 13–15, with symptoms such as headache, vomiting, brief loss of consciousness, transient amnesia, and absence of focal neurological signs, are defined as mild. The aim of this study is to evaluate the stress of children with mild head injuries and their parents’ relevant perception during the early post-traumatic period. Methods: This is a prospective cross-sectional study on a cohort of children with mild head injuries and their parents. Two questionnaires were implemented, the Child Trauma Screening Questionnaire (CTSQ) which was compiled by the children, and the Children’s Revised Impact of Event Scale (CRIES-13), compiled by their parents. Both questionnaires are widely used and reliable. The first presents an exce...

European Psychiatry, 2021

IntroductionChildren with traumatic brain injury (TBI) are at risk for post-traumatic stress diso... more IntroductionChildren with traumatic brain injury (TBI) are at risk for post-traumatic stress disorder (PTSD). The vast majority of TBI are of mild severity (MTBI), however, they may develop persistent neurophysiological symptoms.ObjectivesThe purpose of this study was to investigate the incidence of PTSD in children with MTBI in Western Greece.MethodsA one-year prospective study was conducted at the Children Hospital of Patras. A total of 175 children aged 6-14 years screened for risk of PTSD at one-week and one-month post-injury, completing the Child Trauma Screening Questionnaire (CTSQ). The Children’s Revised Impact of Event Scale (CRIES 13) was administered to the parents, to inquire their assessment of PTSD in the children. Statistical analysis was performed with IBM SPSS v.22.0ResultsThere were 59 (33.7%) children (27.2% boys, 45.9% girls) whose screen result was at risk. At the rescreening one-month postinjury, 9.9% were still at risk. Parents assessed presence of PTSD in 19%...

Estimation of a scale parameter and a quantile

Estimation of P(Y<X) for lognormal distribution

Quality Technology & Quantitative Management

Plants

Eggplant is a widely consumed vegetable, with significant nutritional value and high antioxidant ... more Eggplant is a widely consumed vegetable, with significant nutritional value and high antioxidant content, mainly due to its phenolic constituents. Our goal was to determine the levels of carbohydrates, proteins, total phenolics, anthocyanins, flavonoids, chlorogenic acid, and the antioxidant capacity in thirteen eggplant cultivars cultivated in Greece and to identify sequence polymorphisms in key regulating genes of the phenylpropanoid pathway (C4H, HCT, HQT, C3H, F3H, ANS, MYB1), which might relate to the phytochemical content of those cultivars. The carbohydrates’ content differs among and within cultivars, while the rest of the phytochemicals differ only among cultivars. The cultivars ‘EMI’ and ’Lagkada’ scored higher than the rest in phenolics, anthocyanins, ascorbic acid, caffeoylquinic acid, and antioxidant capacity. Moreover, significant correlations were observed between various ingredients and the antioxidant capacity (FRAP and DPPH). Sequence analysis revealed several SNPs...

Determinants of willingness to pay for urban parks: An empirical analysis in Greece

Land Use Policy

Estimating a linear parametric function of a doubly censored exponential distribution

Statistics, 2017

ABSTRACT For an arbitrary strictly convex loss function, we study the problem of estimating a lin... more ABSTRACT For an arbitrary strictly convex loss function, we study the problem of estimating a linear parametric function is a known constant, when a doubly censored sample is available from a two-parameter exponential population. We establish the inadmissibility of the best affine equivariant (BAE) estimator by deriving an improved estimator. We provide various implications for quadratic and linex loss functions in detail. Improvements are obtained for the absolute value loss function as well. Further a new class of estimators improving upon the BAE estimator is derived using the Kubokawa method. This class is shown to include some benchmark estimators from the literature.

Anxiety and depression among parents of children with mild head injuries

European review for medical and pharmacological sciences, 2021

OBJECTIVE Parents who escort their children in hospital may present emotional disorders. Personne... more OBJECTIVE Parents who escort their children in hospital may present emotional disorders. Personnel pressure and reduced time availability often prevent their detection, reducing the efficacy of parental support. We aimed to identify the prevalence and assess the severity of anxiety and depression among parents of children with mild head injuries who were admitted for a 24-hour observation period in a pediatric hospital, and to detect possible determinants for the severe forms of the two emotional disorders. PATIENTS AND METHODS A cohort of 163 parents participated in our survey for anxiety and depression with the Hospital Anxiety and Depression Scale (HADS). Associations of the two disorders with factors of possible prognostic significance, such as gender, age, family status, residence, education, employment, and income were studied. Multinomial logistic regression analysis, with anxiety and depression of the parents as dependent variables, was performed. RESULTS More than half of p...