New Liu Estimators for the Poisson Regression Model: Method and Application

A new shrinkage estimator for the Poisson model is introduced in this paper. This method is a generalization of the Liu (1993) estimator originally developed for the linear regression model and will be generalised here to be used instead of the classical maximum likelihood (ML) method in the presence of multicollinearity since the mean squared error (MSE) of ML becomes inflated in that situation. Furthermore, this paper derives the optimal value of the shrinkage parameter and based on this value some methods of how the shrinkage parameter should be estimated are suggested. Using Monte Carlo simulation where the MSE and mean absolute error (MAE) are calculated it is shown that when the Liu estimator is applied with these proposed estimators of the shrinkage parameter it always outperforms the ML. Finally, an empirical application has been considered to illustrate the usefulness of the new Liu estimators.Estimation; MSE; MAE; Multicollinearity; Poisson; Liu; Simulation

Inelastic neutron scattering in random binary alloys : an augmented space approach

Combining the augmented space representation for phonons with a generalized version of Yonezawa-Matsubara diagrammatic technique, we have set up a formalism to seperate the coherent and incoherent part of the total intensity of thermal neutron scattering from disordered alloys. This is done exacly without taking any recourse to mean-field like approximation (as done previously). The formalism includes disorder in masses, force constants and scattering lengths. Implementation of the formalism to realistic situations is performed by an augmented space Block recursion which calculates entire Green matrix and self energy matrix which in turn is needed to evaluate the coherent and incoherent intensities. we apply the formalism to NiPd and NiPt alloys. Numerical results on coherent and incoherent scattering cross sections are presented along the highest symmetry directions. Finally the incoherent intensities are compared with the CPA and also with experiments.Comment: 18 pages, 13 figure

Bayesian testing for process capability indices

Process capability indices have been widely used in the manufacturing industry. They measure the ability of a manufacturing process to produce items that meet certain specifications. A capability index relates the voice of the customer (specification limits) to the voice of the process. There is a need to understand and interpret process capability indices. Most of the existing work in this area has been devoted to classical frequentist large sample theory. An alternative approach to the problem of making inference about capability indices is the Bayesian approach. In this paper a Bayesian version of Tukey’s method is used for constructing simultaneous credibility intervals for all pairwise differences. A Bayesian procedure for testing all possible contrasts is also given. The problem of selecting the best supplier(s) has received considerable attention in the literature, but mainly from a classical frequentist point of view. A Bayesian simulation procedure is also illustrated to find the best supplier or group of suppliers.This method seems much easier to perform than the Monte Carlo integration method given in Wu, Shiau, Pearn and Hung (2016). In section 10, a sensitivity analysis regarding the prior choice is considered and in the last section, t-distributed data are analysed

Anomalous thermal expansion in 1D transition-metal cyanides: what makes the novel trimetallic cyanide Cu1/3Ag1/3Au1/3CN behave differently?

The structural dynamics of a quasi-one-dimensional (1D) mixed-metal cyanide, Cu1/3Ag1/3Au1/3CN, with intriguing thermal properties is explored. All the current known related compounds with straight-chain structures, such as group 11 cyanides CuCN, AgCN, AuCN and bimetallic cyanides MxM’1-xCN (M, M’ = Cu, Ag, Au), exhibit 1D negative thermal expansion (NTE) along the chains and positive thermal expansion (PTE) perpendicular to them. Cu1/3Ag1/3Au1/3CN exhibits similar PTE perpendicular to the chains, however PTE, rather than NTE, is also observed along the chains. In order to understand the origin of this unexpected behavior, inelastic neutron scattering (INS) measurements were carried out, underpinned by lattice-dynamical density-functional-theory (DFT) calculations. Synchrotron-based pair-distribution-function (PDF) analysis and 13C solid-state nuclear-magnetic-resonance (SSNMR) measurements were also performed to build an input structural model for the lattice dynamical study. The results indicate that transverse motions of the metal ions are responsible for the PTE perpendicular to the chains, as is the case for the related group 11 cyanides. However NTE along the chain due to the tension effect of these transverse motions is not observed. As there are different metal-to-cyanide bond lengths in Cu1/3Ag1/3Au1/3CN, the metals in neighboring chains cannot all be truly co-planar in a straight-chain model. For this system, DFT-based phonon calculations predict small PTE along the chain due to low-energy chain-slipping modes induced by a bond-rotation effect on the weak metallophilic bonds. However the observed PTE is greater than that predicted with the straight-chain model. Small bends in the chain to accommodate truly co-planar metals provide an alternative explanation for thermal behavior. These would mitigate the tension effect induced by the transverse motions of the metals and, as temperature increases and the chains move further apart, a straightening could occur resulting in the observed PTE. This hypothesis is further supported by unusual evolution in the phonon spectra, which suggest small changes in local symmetry with temperature

Birth weight as an independent predictor of ADHD symptoms : a within-twin pair analysis

BACKGROUND: Studies have found an association between low birth weight and ADHD, but the nature of this relation is unclear. First, it is uncertain whether birth weight is associated with both of the ADHD dimensions, inattentiveness and hyperactivity-impulsivity. Second, it remains uncertain whether the association between birth weight and ADHD symptom severity is confounded by familial factors. METHOD: Parents of all Swedish 9- and 12-year-old twins born between 1992 and 2000 were interviewed for DSM-IV inattentive and hyperactive-impulsive ADHD symptoms by the Autism - Tics, AD/HD and other Comorbidities (A-TAC) inventory (N= 21,775 twins). Birth weight was collected prospectively through the Medical Birth Registry. We used a within-twin pair design to control for genetic and shared environmental factors. RESULTS: Reduced birth weight was significantly associated with a mean increase in total ADHD (beta = -.42; 95% CI: -.53, -.30), inattentive (beta = -.26; 95% CI: -.33, -.19), and hyperactive-impulsive (beta = -.16; 95% CI: -.22, -.10) symptom severity. These results imply that a change of one kilogram of birth weight corresponded to parents rating their child nearly one unit higher (going from "no" to "yes, to some extent" on a given symptom) on the total ADHD scale. These associations remained within pairs of MZ and DZ twins, and were also present when restricting the analyses to full term births. CONCLUSIONS: There is an independent association between low birth weight and all forms of ADHD symptoms, even after controlling for all environmental and genetic confounds shared within twin pairs. These results indicate that fetal growth restriction (as reflected in birth weight differences within twin pairs) and/or the environmental factors which influence it is in the casual pathway leading to ADHD.The Swedish Council for Working Life and Social ResearchThe Swedish Research CouncilManuscrip

On the precipitation hardening of selective laser melted AlSi10Mg

Precipitation hardening of selective laser melted AlSi10Mg was investigated in terms of solution heat treatment and aging duration. The influence on the microstructure and hardness was established, as was the effect on the size and density of Si particles. Although the hardness changes according to the treatment duration, the maximum hardening effect falls short of the hardness of the as-built parts with their characteristic fine microstructure. This is due to the difference in strengthening mechanisms

Familial Liability for Eating Disorders and Suicide Attempts: Evidence From a Population Registry in Sweden

IMPORTANCE: Suicide attempts are common in individuals with eating disorders. More precise understanding of the mechanisms underlying their concomitant occurrence is needed. OBJECTIVE: To examine the association between eating disorders and suicide attempts and whether familial risk factors contribute to the association. DESIGN, SETTING, AND PARTICIPANTS: A Swedish birth cohort including individuals born in Sweden between January 1, 1979, and December 31, 2001, was followed up from age 6 years to December 31, 2009 (N = 2,268,786). Information was acquired from Swedish national registers. All individuals were linked to their biological full siblings, maternal half siblings, paternal half siblings, full cousins, and half cousins. Data analysis was conducted from October 5, 2014, to April 28, 2015. MAIN OUTCOMES AND MEASURES: Eating disorders were captured by 3 variables (any eating disorder, anorexia nervosa, and bulimia nervosa) identified by any lifetime diagnoses recorded in the registers. Suicide attempts were defined as any suicide attempts, including death by suicide, recorded in the registers. We examined the association between eating disorders and death by suicide separately, but the study was underpowered to explore familial liability for this association. RESULTS: Of 2,268,786 individuals, 15,457 females (1.40% of all females) and 991 males (0.09% of all males) had any eating disorder, 7680 females (0.70%) and 453 males (0.04%) had anorexia nervosa, and 3349 females (0.30%), and 61 males (0.01%) had bulimia nervosa. Individuals with any eating disorder had an increased risk (reported as odds ratio [95% CI]) of suicide attempts (5.28 [5.04-5.54]) and death by suicide (5.39 [4.00-7.25]). The risks were attenuated but remained significant after adjusting for comorbid major depressive disorder, anxiety disorder, and substance use disorder (suicide attempts: 1.82 [1.72-1.93]; death by suicide: 2.04 [1.49-2.80]). Similar results were found for anorexia nervosa (suicide attempts: crude, 4.42 [4.12-4.74] vs adjusted, 1.70 [1.56-1.85]; death by suicide: crude, 6.46 [4.38-9.54] vs adjusted, 2.67 [1.78-4.01]) and bulimia nervosa (suicide attempts: crude, 6.26 [5.73-6.85] vs adjusted, 1.88 [1.68-2.10]; death by suicide: crude, 4.45 [2.44-8.11] vs adjusted, 1.48 [0.81-2.72]). Individuals (index) who had a full sibling with any eating disorder had an increased risk of suicide attempts (1.41 [1.29-1.53]). The risk was attenuated for any eating disorder in more-distant relatives (maternal half siblings, 1.10 [0.90-1.34]; paternal half siblings, 1.21 [0.98-1.49]; full cousins, 1.11 [1.06-1.18]; half cousins, 0.90 [0.78-1.03]). This familial pattern remained stable after adjusting for the index individuals' eating disorders. Similar patterns were found for anorexia nervosa and bulimia nervosa. CONCLUSIONS AND RELEVANCE: These results suggest an increased risk of suicide attempts in individuals with lifetime eating disorders and their relatives. The pattern of familial coaggregation suggests familial liability for the association between eating disorders and suicide. Psychiatric comorbidities partially explain this association, suggesting particularly high-risk presentations

Quasiparticle Effective Mass for the Two- and Three-Dimensional Electron Gas

We calculate the quasiparticle effective mass for the electron gas in two and three dimensions in the metallic region. We employ the single particle scattering potential coming from the Sj\"{o}lander-Stott theory and enforce the Friedel sum rule by adjusting the effective electron mass in a scattering calculation. In 3D our effective mass is a monotonically decreasing function of $r_s$ throughout the whole metallic domain, as implied by the most recent numerical results. In 2D we obtain reasonable agreement with the experimental data, as well as with other calculations based on the Fermi liquid theory. We also present results of a variety of different treatments for the effective mass in 2D and 3D.Comment: 12 pages, 2 figure

Use of central nervous system drugs in combination with selective serotonin reuptake inhibitor treatment: a Bayesian screening study for risk of suicidal behavior

Background: Using other central nervous system (CNS) medications in combination with selective serotonin reuptake inhibitor (SSRI) treatment is common. Despite this, there is limited evidence on the impact on suicidal behavior of combining specific medications. We aim to provide evidence on signals for suicidal behavior risk when initiating CNS drugs during and outside of SSRI treatment. Materials and methods: Using a linkage of Swedish national registers, we identified a national cohort of SSRI users aged 6–59 years residing in Sweden 2006–2013. We used a two-stage Bayesian Poisson model to estimate the incidence rate ratio (IRR) of suicidal behavior in periods up to 90 days before and after a CNS drug initiation during SSRI treatment, while accounting for multiple testing. For comparison, and to assess whether there were interactions between SSRIs and other CNS drugs, we also estimated the IRR of initiating the CNS drug without SSRI treatment. Results: We identified 53 common CNS drugs initiated during SSRI treatment, dispensed to 262,721 individuals. We found 20 CNS drugs with statistically significant IRRs. Of these, two showed a greater risk of suicidal behavior after versus before initiating the CNS drug (alprazolam, IRR = 1.39; flunitrazepam, IRR = 1.83). We found several novel signals of drugs that were statistically significantly associated with a reduction in the suicidal behavior risk. We did not find evidence of harmful interactions between SSRIs and the selected CNS drugs. Conclusion: Several of the detected signals for reduced risk correspond to drugs where there is previous evidence of benefit for antidepressant augmentation (e.g., olanzapine, quetiapine, lithium, buspirone, and mirtazapine). Novel signals of reduced suicidal behavior risk, including for lamotrigine, valproic acid, risperidone, and melatonin, warrant further investigation