Alternative distributions for observation driven count series models

Observation-driven models provide a flexible framework for modelling time series of counts. They are able to capture a wide range of dependence structures. Many applications in this field of research are concerned with count series whose conditional distribution given past observations and explanatory variables is assumed to follow a Poisson distribution. This assumption is very convenient since the Poisson distribution is simple and leads to models which are easy to implement. On the other hand this assumption is often too restrictive since it implies equidispersion, the fact that the conditional mean equals the conditional variance. This assumption is often violated in empirical applications. Therefore more flexible distributions which allow for overdispersion or underdispersion should be used. This paper is concerned with the use of alternative distributions in the framework of observationdriven count series models. In this paper different count distributions and their properties are reviewed and used for modelling. The models under consideration are applied to a time series of daily counts of asthma presentations at a Sydney hospital. This data set has already been analyzed by Davis et al. (1999, 2000). The Poisson-GLARMA model proposed by these authors is used as a benchmark. This paper extends the work of Davis et al. (1999) to distributions which are nested in either the generalized negative binomial or the generalized Poisson distribution. Additionally the maximum likelihood estimation for observation-driven models with generalized distributions is presented in this paper. --Count series,observation-driven models,GLARMA,dicrete distributions

Alternative distributions for observation driven count series models

Observation-driven models provide a flexible framework for modelling time series of counts. They are able to capture a wide range of dependence structures. Many applications in this field of research are concerned with count series whose conditional distribution given past observations and explanatory variables is assumed to follow a Poisson distribution. This assumption is very convenient since the Poisson distribution is simple and leads to models which are easy to implement. On the other hand this assumption is often too restrictive since it implies equidispersion, the fact that the conditional mean equals the conditional variance. This assumption is often violated in empirical applications. Therefore more flexible distributions which allow for overdispersion or underdispersion should be used. This paper is concerned with the use of alternative distributions in the framework of observationdriven count series models. In this paper different count distributions and their properties are reviewed and used for modelling. The models under consideration are applied to a time series of daily counts of asthma presentations at a Sydney hospital. This data set has already been analyzed by Davis et al. (1999, 2000). The Poisson-GLARMA model proposed by these authors is used as a benchmark. This paper extends the work of Davis et al. (1999) to distributions which are nested in either the generalized negative binomial or the generalized Poisson distribution. Additionally the maximum likelihood estimation for observation-driven models with generalized distributions is presented in this paper

ANS 490-A: Ewe Lamb’sTemperament and Effects on Maze Entry, Exit Order and Coping Styles When Exposed to Novel Stimulus

Theobjectivesof this experiment were (1) to determine if experienceaffects maze entrance and exit order and (2) how temperament affects ewe lamb coping response to a predictable novel stimulus. A total of nine, ~4-month-old blackface Hampshire-cross ewe lambs, BW~18 to 27 kg were used.Ewe lamb temperament was identified and three groups of ewe lambs were created. Each group hada BOLD, MODERATEand SHYewe lamb.All ewe lambs were introduced and habituated to themaze for four consecutive days (days -3 to day 0),respectively.On trial day 1, Group 1 (EXPERIENCED)passed through the maze. On trial day 2, Groups 1 and 2 (MIDDLE) passed through the maze. On trial day 3, Groups 1, 2 and 3 (NAÏVE) passed through the maze. Over these trial days, ewe lambs were exposed to a red ball and a red flag (novel stimuli). Behavioral measures(order to enter and exit the maze and coping style [active vs passive]) werecollected over four habituation days (-3, -2, -1 and0), and over three trialdays (1, 2 and 3),respectively.The data will be presented descriptively. Ewe lamb 1936 had the highest number of cone touches, with 1943 having the leastover the 1-h observation period. For the BOLDgroup the cone touches ranged from 7 to 10, MODERATEranged from 5 to 6 and SHYranged from 0 to 4 respectively. Over all entry days a BOLDewe lamb entered and exited the maze first, but it was not always the same BOLDewe lamb. There was no consistent ewe lamb order for entering or exiting the maze for MODERATEor SHYtemperament classification. Ewe lambs for both stimuli engaged in a passive coping style (77.8%). In conclusion, ewe lambs, regardless of temperament, did not react negatively to a novel stimuli. Furthermore, experience to the maze did not affect entrance and exit order and all ewe lambs navigated the maze in less than 15-seconds over all trial days. We predict that this behavioral reactivity would enable producers to handle ewe lambs effectively in a handling system for necessary husbandry practices without undue animal welfare issues

Introducing LoCo, a Logic for Configuration Problems

In this paper we present the core of LoCo, a logic-based high-level representation language for expressing configuration problems. LoCo shall allow to model these problems in an intuitive and declarative way, the dynamic aspects of configuration notwithstanding. Our logic enforces that configurations contain only finitely many components and reasoning can be reduced to the task of model construction.Comment: In Proceedings LoCoCo 2011, arXiv:1108.609

Exploring unsymmetrical diboranes(4) as boryl ligand precursors: platinum(ii) bis-boryl complexes

A series of five unsymmetrical platinum(II) bis-boryl complexes, bearing two distinct boryl ligands, are obtained by the oxidative addition reaction of unsymmetrical diborane(4) derivatives, bearing either two different dialkoxy or one dialkoxy and one diamino boryl moiety, with [(Ph3P)2Pt(C2H4)]. All five complexes were structurally and spectroscopically characterised. The bis-boryl platinum(II) complexes exhibit slightly distorted square-planar cis-boryl structures with acute B–Pt–B angles, short B/B distances of 2.44–2.55 °A and relatively long trans-boryl P–Pt distances around 2.34 °A. The 31P–195Pt NMR coupling constants are indicative for the strongly donating/trans-influencing boryl ligands. Despite the structural and spectroscopic data at hand no finally conclusive order of the donor properties/transinfluence of the boryl ligands can be deduced on the basis of these data. This may be explained by an (residual) interaction of two boryl ligands

Global urbanization and food production in direct competition for land: Leverage places to mitigate impacts on SDG2 and on the Earth System

Global urbanization and food production are in direct competition for land. This paper carries out a critical review of how displacing crop production from urban and peri-urban land to other areas – because of issues related to soil quality – will demand a substantially larger proportion of the Earth’s terrestrial land surface than the surface area lost to urban encroachment. Such relationships may trigger further distancing effects and unfair social-ecological teleconnections. It risks also setting in motion amplifying effects within the Earth System. In combination, such multiple stressors set the scene for food riots in cities of the Global South. Our review identifies viable leverage points on which to act in order to navigate urban expansion away from fertile croplands. We first elaborate on the political complexities in declaring urban and peri-urban lands with fertile soils as one global commons. We find that the combination of an advisory global policy aligned with regional policies enabling robust common properties rights for bottom-up actors and movements in urban and peri-urban agriculture (UPA) as multi-level leverage places to intervene. To substantiate the ability of aligning global advisory policy with regional planning, we review both past and contemporary examples where empowering local social-ecological UPA practices and circular economies have had a stimulating effect on urban resilience and helped preserve, restore, and maintain urban lands with healthy soils

The Coptic Wizard's Hoard

This is the publisher's version, also available electronically from http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=7824067&fileId=S0017816000030224.Within the large collection of ancient manuscripts at the University of Michigan there is a group of Coptic papyri which appears to have been a hoard or library of ancient magical texts. Produced by five copyists sometime in the fourth through seventh centuries and originating from a now unknown location in Egypt, the collection was brought to the British Museum by Sir E. A. Wallis Budge in February 1921 for restoration by C. T. Lamacraft; in August of that year, it underwent philological examination by the Coptic lexicographer Walter E. Crum, and was later forwarded to the University of Michigan

Zigzag Turning Preference of Freely Crawling Cells

The coordinated motion of a cell is fundamental to many important biological processes such as development, wound healing, and phagocytosis. For eukaryotic cells, such as amoebae or animal cells, the cell motility is based on crawling and involves a complex set of internal biochemical events. A recent study reported very interesting crawling behavior of single cell amoeba: in the absence of an external cue, free amoebae move randomly with a noisy, yet, discernible sequence of ‘run-and-turns’ analogous to the ‘run-and-tumbles’ of swimming bacteria. Interestingly, amoeboid trajectories favor zigzag turns. In other words, the cells bias their crawling by making a turn in the opposite direction to a previous turn. This property enhances the long range directional persistence of the moving trajectories. This study proposes that such a zigzag crawling behavior can be a general property of any crawling cells by demonstrating that 1) microglia, which are the immune cells of the brain, and 2) a simple rule-based model cell, which incorporates the actual biochemistry and mechanics behind cell crawling, both exhibit similar type of crawling behavior. Almost all legged animals walk by alternating their feet. Similarly, all crawling cells appear to move forward by alternating the direction of their movement, even though the regularity and degree of zigzag preference vary from one type to the other