Mixed-Mode Oscillations Due to a Singular Hopf Bifurcation in a Forest Pest Model

In a forest pest model, young trees are distinguished from old trees. The pest feeds on old trees. The pest grows on a fast scale, the young trees on an intermediate scale, and the old trees on a slow scale. A combination of a singular Hopf bifurcation and a “weak return” mechanism, characterized by a small change in one of the variables, determines the features of the mixed-mode oscillations. Period-doubling and saddle-node bifurcations lead to closed families (called isolas) of periodic solutions in a bifurcation corresponding to a singular Hopf bifurcation.     

Prevalence of gambling problems among adolescents in the Nordic countries: an overview of national gambling surveys 1997–2009

Kristiansen S, Jensen SM. Prevalence of gambling problems among adolescents in the Nordic countries: an overview of national gambling surveys 1997–2009 Int J Soc Welfare 2011: 20: 75–86 © 2009 The Author(s), Journal compilation © 2009 Blackwell Publishing Ltd and the International Journal of Social Welfare. The study presents an overview of prevalence studies focusing on problem and pathological gambling among adolescent populations in the Nordic countries. Past‐year prevalence of problem gambling among adolescents in the Nordic countries ranges from 0.4 per cent (Denmark) to 4.2 per cent (Sweden). Past‐year prevalence of pathological gambling ranges from 0.1 per cent (Denmark) to 1.76 per cent (Norway). Results from the Nordic countries also show that boys gamble more than girls, older adolescents gamble more than younger adolescents and that, as shown in adult prevalence surveys, problem gambling is more widespread among adolescents than among adults. It is concluded that investigations of gambling problems among adolescents in the Nordic countries differ regarding age groups, sampling procedures, response rates, nomenclature and screening instruments, all of which complicates valid comparisons. More collaboration between researchers from different countries is urged in order to improve comparability between national studies.     

Justification of functional form assumptions in structural models: applications and testing of qualitative measurement axioms

In both theoretical and applied modeling in behavioral sciences, it is common to choose a mathematical specification of functional form and distribution of unobservables on grounds of analytic convenience without support from explicit theoretical postulates. This article discusses the issue of deriving particular qualitative hypotheses about functional form restrictions in structural models from intuitive theoretical axioms. In particular, we focus on a family of postulates known as dimensional invariance. Subsequently, we discuss how specific qualitative postulates can be reformulated so as to allow for conventional statistical hypothesis testing, and we also derive details of a particular likelihood ratio test procedure. An empirical application of the testing procedure is carried out, based on data from a Stated Preference survey.     

Statistical Corrections of Invalid Correlation Matrices

Suppose estimates are available for correlations between pairs of variables but that the matrix of correlation estimates is not positive definite. In various applications, having a valid correlation matrix is important in connection with follow‐up analyses that might, for example, involve sampling from a valid distribution. We present new methods for adjusting the initial estimates to form a proper, that is, nonnegative definite, correlation matrix. These are based on constructing certain pseudo‐likelihood functions, formed by multiplying together exact or approximate likelihood contributions associated with the individual correlations. Such pseudo‐likelihoods may then be maximized over the range of proper correlation matrices. They may also be utilized to form pseudo‐posterior distributions for the unknown correlation matrix, by factoring in relevant prior information for the separate correlations. We illustrate our methods on two examples from a financial time series and genomic pathway analysis.     

Hidden in full view: the organization of public secrecy in Miéville’s The City and the City

ABSTRACT

In this article, we explore China Mieville’s novel The City and the City as a literary experiment for analyzing the dynamics of public secrecy. We explore public secrets as an intrinsic part of organizational life and as a framework for paying attention to the politics of organizing. First, we focus on the novel’s invention and use of the verb ‘unseeing’ to bring out the embodied and sensuous aspects of public secrecy as part of organizational processes. Second we unfold how, although the content of public secrets may turn out to be less spectacular than expected, it is exactly their mundaneness which is key to their political importance. This is important because in an increasingly disorganized and uncertain world, secrecy proliferates and the visibility of secrecy is often a strategic move to justify certain hidden actions.     

The Wally plot approach to assess the calibration of clinical prediction models

Lifetime Data Analysis - A prediction model is calibrated if, roughly, for any percentage x we can expect that x subjects out of 100 experience the event among all subjects that have a predicted...     

Social Competence and Antisocial Behavior: Continuity and Distinctiveness Across Early Adolescence

The degree of continuity and distinctiveness in social competence and antisocial behavior was examined in a longitudinal structural equation model. Participants were 391 typically developing Norwegian middle school students (51% boys), their parents, and teachers and were assessed when they were approximately 13 years of age (a school cohort in 8th grade) and again 17 months later, when they were about 15 years old (in 10th grade). Social competence showed considerable stability across middle school, more than did antisocial behavior. Low social competence at age 13 predicted antisocial behavior at age 15, over and above the variance explained by the earlier assessment of antisocial behavior. While social competence and antisocial behavior both showed a relatively strong negative association concurrently and demonstrated considerable overlap, results suggested that the two constructs should be considered separate dimensions. Findings are presented within a transactional framework and implications for prevention efforts and directions for future research are discussed.     

NON‐PARAMETRIC BAYESIAN INFERENCE FOR INHOMOGENEOUS MARKOV POINT PROCESSES

With reference to a specific dataset, we consider how to perform a flexible non‐parametric Bayesian analysis of an inhomogeneous point pattern modelled by a Markov point process, with a location‐dependent first‐order term and pairwise interaction only. A priori we assume that the first‐order term is a shot noise process, and that the interaction function for a pair of points depends only on the distance between the two points and is a piecewise linear function modelled by a marked Poisson process. Simulation of the resulting posterior distribution using a Metropolis–Hastings algorithm in the ‘conventional’ way involves evaluating ratios of unknown normalizing constants. We avoid this problem by applying a recently introduced auxiliary variable technique. In the present setting, the auxiliary variable used is an example of a partially ordered Markov point process model.