Positive quadrant dependence tests for copulas

In this paper the interest is in testing the null hypothesis of positive quadrant dependence (PQD) between two random variables. Such a testing problem is important since prior knowledge of PQD is a qualitative restriction that should be taken into account in further statistical analysis, for example, when choosing an appropriate copula function to model the dependence structure. The key methodology of the proposed testing procedures consists of evaluating a “distance” between a nonparametric estimator of a copula and the independence copula, which serves as a reference case in the whole set of copulas having the PQD property. Choices of appropriate distances and nonparametric estimators of copula are discussed, and the proposed methods are compared with testing procedures based on bootstrap and multiplier techniques. The consistency of the testing procedures is established. In a simulation study the authors investigate the finite sample size and power performances of three types of test statistics, Kolmogorov–Smirnov, Cramér–von‐Mises, and Anderson–Darling statistics, together with several nonparametric estimators of a copula, including recently developed kernel type estimators. Finally, they apply the testing procedures on some real data. The Canadian Journal of Statistics 38: 555–581; 2010 © 2010 Statistical Society of Canada     

Potency Factors for Risk Assessment at Libby,Montana

We reanalyzed the Libby vermiculite miners’ cohort assembled by Sullivan to estimate potency factors for lung cancer, mesothelioma, nonmalignant respiratory disease (NMRD), and all‐cause mortality associated with exposure to Libby fibers. Our principal statistical tool for analyses of lung cancer, NMRD, and total mortality in the cohort was the time‐dependent proportional hazards model. For mesothelioma, we used an extension of the Peto formula. For a cumulative exposure to Libby fiber of 100 f/mL‐yr, our estimates of relative risk (RR) are as follows: lung cancer, RR = 1.12, 95% confidence interval (CI) =[1.06, 1.17]; NMRD, RR = 1.14, 95% CI =[1.09, 1.18]; total mortality, RR = 1.06, 95% CI =[1.04, 1.08]. These estimates were virtually identical when analyses were restricted to the subcohort of workers who were employed for at least one year. For mesothelioma, our estimate of potency is K_M = 0.5 × 10^?8, 95% CI =[0.3 × 10^?8, 0.8 × 10^?8]. Finally, we estimated the mortality ratios standardized against the U.S. population for lung cancer, NMRD, and total mortality and obtained estimates that were in good agreement with those reported by Sullivan. The estimated potency factors form the basis for a quantitative risk assessment at Libby.     

What makes foster carers think about quitting? Recommendations for improved retention of foster carers

Ideation, or the formulation of ideas pertaining to a particular topic, is the precursor to individuals making significant life decisions. Many individuals think about foster caring long before they actually become carers, and it stands to reason that in many cases, carer discontinuation also follows a period of ideation. This being the case, it is possible that by monitoring ideation, interventions could be introduced to prevent placement disruptions occurring, particularly if the sources of dissatisfaction are known. Using a sample of 205 foster carers, a posteriori segmentation analysis identifies groups of carers dissatisfied with the same aspects of their role. One group is particularly dissatisfied with factors that are within the control of foster care agencies and also reports high levels of discontinuation ideation. Recommendations include that the individual support needs of carers be identified such that customized support can be offered, including boosting initial and ongoing training to manage expectations and ensure carers feel prepared for the role. Results also highlight the important role of caseworkers in making carers feel appreciated and taken seriously.     

Methods for Classifying Nonprofit Organizations According to their Field of Activity: A Report on Semi-automated Methods Based on Text

VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations - There are various methods for classifying nonprofit organizations (NPOs) according to their field of activity. We report...     

With or Without You?1 Strategic Spatial Planning and Territorial Re-Scaling in Grenoble Urban Region

Spatial planning across European city regions is undergoing substantial changes. The paper draws on the framework of territorial re-scaling, strategic spatial planning and the emergence of new governance modes in order to analyse strategic planning episodes in Grenoble urban region (France). The paper aims at showing how strategic planning processes by means of new governance arenas call into question local planning cultures, especially by reshaping planning perimeters, territorial identities and actors' roles. In particular, it shows the importance of path dependency for strategic planning, the effects of power imbalances between local actors and the crucial role planners play in spatial policy-making.     

Improved nearest neighbor classifiers by weighting and selection of predictors

Nearest neighborhood classification is a flexible classification method that works under weak assumptions. The basic concept is to use the weighted or un-weighted sums over class indicators of observations in the neighborhood of the target value. Two modifications that improve the performance are considered here. Firstly, instead of using weights that are solely determined by the distances we estimate the weights by use of a logit model. By using a selection procedure like lasso or boosting the relevant nearest neighbors are automatically selected. Based on the concept of estimation and selection, in the second step, we extend the predictor space. We include nearest neighborhood counts, but also the original predictors themselves and nearest neighborhood counts that use distances in sub dimensions of the predictor space. The resulting classifiers combine the strength of nearest neighbor methods with parametric approaches and by use of sub dimensions are able to select the relevant features. Simulations and real data sets demonstrate that the method yields better misclassification rates than currently available nearest neighborhood methods and is a strong and flexible competitor in classification problems.     

Monitoring correlation change in a sequence of random variables

We propose a monitoring procedure to test for the constancy of the correlation coefficient of a sequence of random variables. The idea of the method is that a historical sample is available and the goal is to monitor for changes in the correlation as new data become available. We introduce a detector which is based on the first hitting time of a CUSUM-type statistic over a suitably constructed threshold function. We derive the asymptotic distribution of the detector and show that the procedure detects a change with probability approaching unity as the length of the historical period increases. The method is illustrated by Monte Carlo experiments and the analysis of a real application with the log-returns of the Standard & Poor's 500 (S&P 500) and IBM stock assets.     

Digitalisierung und Konvergenz von Online- und Offline-Welt

The increasing diffusion of mobile phones with internet access (Smartphones) enables more and more consumers to use the mobile internet. In addition, there is a continuing integration of location-based services (LBS). By means of Global Positioning Systems or WiFi-triangulation LBS provide context-aware information to consumers. This leads to a convergence of online and offline worlds. The usage of LBS delivers additional information to consumers (e.g. alternative offers or detailed product information). Therefore LBS do have an influence on consumer behavior. Particularly during the search process, information about prices or geographic distances, that are relevant for the purchase, are of importance. This study analyzes the relevance of location-based internet search empirically. Search costs are estimated on an individual level in a choice-based conjoint analysis using two different products. As a result, location-based internet search is considered to be very relevant for search and influential on consumer behavior. The study shows different consumers preferences and different search costs depending on the product. To conclude the study, the implications are discussed. The major contribution of this study is that it shows that offline and online search do have a mutual impact on each other. Furthermore, search costs are measured in a mobile context.     

T Cell Immunity and Aging

The effect of age on the immune system is generally detrimental and results in "immunosenescence," a poorly-defined state inadequately reflected in clinical data and for which few reliable "biomarkers of aging" are available. The multinational consortium "T-Cell Immunity in Ageing," T-CIA, was set up to examine these issues specifically as applied to T lymphocytes. This Perspective discusses some of the outcomes of a recent conference that considered progress toward resolving these questions in humans.