Two-Piece location-scale distributions based on scale mixtures of normal family

In this work, we study the maximum likelihood (ML) estimation problem for the parameters of the two-piece (TP) distribution based on the scale mixtures of normal (SMN) distributions. This is a family of skewed distributions that also includes the scales mixtures of normal class, and is flexible enough for modeling symmetric and asymmetric data. The ML estimates of the proposed model parameters are obtained via an expectation-maximization (EM)-type algorithm.     

Suicide clusters: introducing a novel type of categorization

A suicide cluster within a given community may be defined as a group of suicides or suicide attempts, or both, that happen closer together in time and space than would generally be expected. However, since the perception of clustering may itself be a risk factor for suicide, suicide clusters differ almost from all other event clusters. The aim of this article, therefore, is to discuss the unique pattern of suicide cluster and introduce a novel type of categorization taking into account varieties of studies, which investigate suicide clusters within diverse settings. This article concludes with challenging areas in suicide cluster studies and emphasizing that each community must deal rapidly and appropriately with any perceived suicide clusters.     

A Bayesian approach on the two-piece scale mixtures of normal homoscedastic nonlinear regression models

In this application note paper, we propose and examine the performance of a Bayesian approach for a homoscedastic nonlinear regression (NLR) model assuming errors with two-piece scale mixtures of normal (TP-SMN) distributions. The TP-SMN is a large family of distributions, covering both symmetrical/ asymmetrical distributions as well as light/heavy tailed distributions, and provides an alternative to another well-known family of distributions, called scale mixtures of skew-normal distributions. The proposed family and Bayesian approach provides considerable flexibility and advantages for NLR modelling in different practical settings. We examine the performance of the approach using simulated and real data.KEYWORDS: Gibbs sampling, MCMC method, nonlinear regression model, scale mixtures of normal family, two-piece distributions     

Pattern of prenatal care utilization in Tehran: A population based longitudinal study

Aim

To assess the pattern of prenatal care utilization in Tehran in 2015.

On a hybrid data cloning method and its application in generalized linear mixed models

The data cloning method is a new computational tool for computing maximum likelihood estimates in complex statistical models such as mixed models. This method is synthesized with integrated nested Laplace approximation to compute maximum likelihood estimates efficiently via a fast implementation in generalized linear mixed models. Asymptotic behavior of the hybrid data cloning method is discussed. The performance of the proposed method is illustrated through a simulation study and real examples. It is shown that the proposed method performs well and rightly justifies the theory. Supplemental materials for this article are available online.     

Designing an ergonomics backpack for student aged 7-9 with user centred design approach

Researches explored that backpacks are the most common means of carrying school supplies for students. Carrying heavy backpacks causes a wide range of disorders such as musculoskeletal disorders and postural malfunction. User Centered Design has proven its suitability to produce high efficient products with the most adaptability to consumer demands. This approach combined with consideration of normal standards and ergonomics features, with the recognition of children's needs and requirements, has been used in this research to prepare an initial design of a backpack. After that, its prototype was manufactured. The backpack was tested by 120 elementary students in three steps of form, ergonomics and load sense. A redesign was performed that has applied the results of the test run. Results showed that this new backpack can considerably reduce the effective loads on the shoulders, back and neck.     

Forecasting daily outflows from a bank account

This paper is concerned with forecasting the total dollar amounts of checks presented for payment against a company bank account. Checks are issued each day against the account and mailed to parties located in different parts of the country. The mail lag for each check is taken into account explicitly given that data on this variable are readily available from external sources. Based on the distribution of time until clearance of each check after its receipt, the probability distribution of the total amount presented for payment on each day between consecutive bank statements can be readily computed one day ahead. A procedure for implementation of this forecasting scheme is suggested.     

The microanatomy of trabecular bone in young normal and osteoporotic elderly males

Normally there is a gradual continual loss of cortical and trabecular bone in both men and women as they age. Osteopenia and osteoporosis are conditions in which the loss results in brittle bones that fracture easily. Males with low testosterone and hypogonadism are predisposed to osteoporosis and prevention tends to be overshadowed by the greater problem in postmenopausal women. The ability of the skeleton to resist external forces depends partly upon the amount of bone present and partly upon other factors including cancellous bone microarchitecture. This is examined in iliac crest bone biopsies from idiopathic osteoporotic men, mean age 60 ± 12 SD years [n = 16]. These were compared with a healthy control group (autopsy samples), mean age 30 ± 8.9 years [n = 28] with the aim of examining the pattern of cancellous atrophy in male idiopathic osteoporosis. Undecalcified specimens were embedded in methylmethacrylate and prepared for histomorphometry. Sections were analysed using an automated trabecular analysis system (TAS), whereby a binary image was created. Area measurements including the trabecular surface and distance measurements including the trabecular width were made. The binary image was thinned to its medial framework and the node and terminus number as indices of trabecular interconnection were recorded, together with the strut length. Results (median (range)) showed a lower percentage bone volume in the elderly osteoporotic male, 10.2% (5.4–23.1) compared to young normals 25.2% (14.6–43.9), p < 0.001. The trabeculae tended to be thinner, 95.7 µm (66.7–170.7) c.f. 120.8 µm (75.8–208.6) and considerably fewer in number, 11.1 (2.1–31.4) c.f. 48.3 (25.4–66.9), p < 0.001 per field and in particular the number of nodes, 2.1 (0.15–14) c.f. 40.6 (10.3–74.1) per field and the node: terminus ratio fell to 0.13 (0.01–1.19) c.f. controls 0.98 (0.24–6.69), p < 0.001. It was concluded that the pattern of cancellous atrophy in male idiopathic osteoporosis differs from normal aging and resembles that in postmenopausal women. Results using the automated TAS confirm previous observations made manually.     

Skew-Normal ARMA Models with Nonlinear Heteroscedastic Predictors

Multivariate skew-normal (SN) distributions (Azzalini and Dalla Valle, 1996 Azzalini , A. , Dalla Valle , A. ( 1996 ). The multivariate skew-normal distribution . Biometrika 83 : 715 – 726 .[Crossref], [Web of Science ®] , [Google Scholar]) enjoy some of the useful properties of normal distributions, have nonlinear heteroscedastic predictors but lack the closure property of normal distributions (the sum of independent SN random variables is not SN). Recently, there has been a proliferation of classes of SN distributions with certain closure properties, one of the most promising being the closed skew-normal (CSN) distributions of González-Farías et al. (2004 González-Farías , G. , Dominguez-Molina , J. A. , Gupta , A. K. ( 2004 ). Additive properties of skew-normal random vectors . J. Statist. Plann. Infer. 126 : 521 – 534 .[Crossref], [Web of Science ®] , [Google Scholar]). We study the construction of stationary SN ARMA models for colored SN noise and show that their finite-dimensional distributions are skew-normal, seldom strictly stationary and their covariance functions differ from their normal ARMA counterparts in that they do not converge to zero for large lags. The situation is better for ARMA models driven by CSN noise, but at the additional cost of considerable computational complexity and a less explicit skewness parameter. In view of these results, the widespread use of such classes of SN distributions in the framework of ARMA models seem doubtful.     

Multivariate Aging with Archimedean Dependence Structures in High Dimensions

Bivariate aging notions for a vector X of lifetimes based on stochastic comparisons between X and X _t, where X _t is the multivariate residual lifetime after time t > 0, have been studied in Pellerey (2008 Pellerey , F. ( 2008 ). On univariate and bivariate aging for dependent lifetimes with Archimedean survival copulas . Kybernetika 44 : 795 – 806 .[Web of Science ®] , [Google Scholar]) under the assumption that the dependence structure in X is described by an Archimedean survival copula. Similar stochastic comparisons between X _t and X _t+s, for all t; s > 0, were considered in Mulero and Pellerey (2010 Mulero , J. , Pellerey , F. ( 2010 ). Bivariate aging properties under Archimedean dependence structures . Commun. Statist. Theor. Meth. 39 : 3108 – 3121 .[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). In this article, these results are generalized and extended to the multivariate case. Two illustrative examples are also provided.