Volunteering and Civic Action: Boundaries Blurring,Boundaries Redrawn

VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations - The aim of this introduction to the special issue is to call into question the presumed conceptual divide between...     

Benefit dependency: The pros and cons of using “caseload” data for national and international comparisons

Policy‐makers in advanced welfare states have increasingly expressed concerns over large numbers of working‐age people claiming social security support. Accordingly, policies aimed at reducing the level of “benefit dependency” have gained prominence. However, such policies rest on shaky empirical evidence. Systematic collections of national “caseload” data are rare, social security programmes overlap and administrative categories vary over time. The internationally inconsistent treatment of national transfer programmes provides a further challenge for cross‐national comparisons. This article first identifies and discusses several of these problems, and ways in which they may be addressed. It then employs administrative claimant data from six European countries as a way of illustrating trends over time and across countries. The underlying aim is to explore the scientific potential of benefit recipient numbers as an indicator for welfare state change over time and across countries.     

Correction to: Mixed methods research: what it is and what it could be

Theory and Society - Unfortunately, figure 2 was incorrectly published.     

The Right Price of Food

Only a few years ago the widely shared view was that low food prices were a curse to developing countries and the poor. Their dramatic increase in 2006–8 appears to have altered this view fundamentally. High food prices are now judged to have a devastating effect on developing countries and the world's poor – a reversal of opinion that raises questions about the old and the new arguments and the proposed remedies, and also about the causes of this dramatic turnaround in analysis and policy conclusions. This article puts these changes in perspective and discusses their potential implications.     

Subset Selection in Linear Regression using Sequentially Normalized Least Squares: Asymptotic Theory

This article examines the recently proposed sequentially normalized least squares criterion for the linear regression subset selection problem. A simplified formula for computation of the criterion is presented, and an expression for its asymptotic form is derived without the assumption of normally distributed errors. Asymptotic consistency is proved in two senses: (i) in the usual sense, where the sample size tends to infinity, and (ii) in a non‐standard sense, where the sample size is fixed and the noise variance tends to zero.     

Modeling Individual Cell Lag Time Distributions for Listeria monocytogenes

The food industry faces two paradoxical demands: on the one hand, foods need to be microbiologically safe for consumption and on the other hand, consumers want fresh, minimally processed foods. To meet these demands, more insight into the mechanisms of microbial growth is needed, which includes, among others, the microbial lag phase. This is the time needed by bacterial cells to adapt to a new environment (for example, after food product contamination) before starting an exponential growth regime. Since food products are often contaminated with low amounts of pathogenic microorganisms, it is important to know the distribution of these individual cell lag times to make accurate predictions concerning food safety. More precisely, cells with the shortest lag times (i.e., appearing in the left tail of the distribution) are largely decisive for the outgrowth of the population. In this study, an integrated modeling approach is proposed and applied to an existing data set of individual cell lag time measurements of Listeria monocytogenes. In a first step, a logistic modeling approach is applied to predict the fraction of zero-lag cells (which start growing immediately) as a function of temperature, pH, and water activity. For the nonzero-lag cells, the mean and variance of the lag time distribution are modeled with a hyperbolic-type model structure. This mean and variance allow identification of the parameters of a two-parameter Weibull distribution, representing the nonzero-lag cell lag time distribution. The integration of the developed models allows prediction of a global distribution of individual cell lag times for any combination of environmental conditions in the interpolation domain of the original temperature, pH, and water activity settings. The global fitting quality of the model is quantified using several measures indicating that the model gives accurate predictions, erring slightly on the fail-safe side when predicting the shortest lag times.     

Polynomial Primal-Dual Affine Scaling Algorithms in Semidefinite Programming

Two primal-dual affine scaling algorithms for linear programming are extended to semidefinite programming. The algorithms do not require (nearly) centered starting solutions, and can be initiated with any primal-dual feasible solution. The first algorithm is the Dikin-type affine scaling method of Jansen et al. (1993b) and the second the classical affine scaling method of Monteiro et al. (1990). The extension of the former has a worst-case complexity bound of O(₀nL) iterations, where ₀ is a measure of centrality of the the starting solution, and the latter a bound of O(₀nL²) iterations.