Computation of determinantal subset influence in regression

One of the important goals of regression diagnostics is the detection of cases or groups of cases which have an inordinate impact on the regression results. Such observations are generally described as influential. A number of influence measures have been proposed, each focusing on a different aspect of the regression. For single cases, these measures are relatively simple and inexpensive to calculate. However, the detection of multiple-case or joint influence is more difficult on two counts. First, calculation of influence for a single subset is more involved than for an individual case, and second, the sheer number of subsets of cases makes the computation overwhelming for all but the smallest data sets.Barrett and Gray (1992) described methods for efficiently examining subset influence for those measures that can be expressed as the trace of a product of positive semidefinite (psd) matrices. There are, however, other popular measures that do not take this form, but rather are expressible as the ratio of determinants of psd matrices. This article focuses on reducing the computation for the determinantal ratio measures by making use of upper and lower bounds on the influence to limit the number of subsets for which the actual influence must be explicitly determined.     

A reply to Mr Palloni's comments

Abstract The protracted and inconclusive debate on the cause of the post-war mortality decline in Ceylon reflects our ignorance of this complex historical event and although I am reticent to prolong this already lengthy discussion, I feel that it is necessary to reply to certain points raised by Mr Palloni. The object of my paper 'The Decline of Mortality in Ceylon and the Demographic Effects of Malaria Control'(9) was to re-examine some of the past work on this subject in order to attempt a synthesis of previous theories, was not, however, intended to provide a definitive account of all the causal mechanisms underlying the decline of mortality as it is my view that the data are insufficient for such an undertaking. In the reappraisal I was mainly concerned with the validity of Newman's regression model and, as far as the data would permit, an assessment of Meegama's thesis that there were significant disturbing variables which confounded the simple regression of mortality decline and malaria prevalence. I will try first to respond to Mr Palloni's specific substantive points and then go on to consider the broader question of regression models.     

Internationalization,Innovation and Institutions: The 3 I's Underpinning the Competitiveness of Emerging Market Firms

The past decade has seen an increase in the extent of research focused on and around emerging market firms (EMFs) and their rising levels of competitiveness in both their home markets and more importantly in the global market place. At the same time, the practitioner-oriented literature has been documenting a growing number of corporate success stories that originate in emerging market economies. We posit that the growing prominence of EMFs is a result of three interrelated phenomena: the fast-paced internationalization of EMFs into both developing and developed market economies; the rapidly increasing extent to which business enterprises in emerging economies are focusing on knowledge-intensive processes and innovation; and the continuous evolution of institutions in these markets, particularly in terms of economic liberalization.     

Testing the Vitamin Model of job stress in Dutch health care workers

Three central hypotheses of Warr's Vitamin Model concerning the relationship between job characteristics and well-being and health outcomes were tested: (1) differential effects of job characteristics on the various well-being and health outcomes; (2) predominance of curvilinear associations; and (3) moderate influence of negative and positive affectivity on these relationships. The study participants were 162 employees from a health care organization (aged 19-54 years, 95% women) who completed questionnaires on job demands and job autonomy, as well as on the outcome variables depression, anxiety, job satisfaction, and health complaints. In addition, data on short-term sickness absence were collected. A higher level of job demands was significantly associated with a lower level of well-being and self-reported health. Job autonomy showed weaker relationships with the outcome variables. The effects of job demands were still large after controlling for negative and positive affectivity, while the effects of job autonomy in most cases became non-significant. The predicted curvilinear relationship between job characteristics and outcome variables did not have an additional value over a linear model in predicting the data. It is concluded that the present data from a homogeneous sample of mostly female nurses support Warr's Vitamin Model to a limited extent.     

Understanding Management Performance

Current models of the factors underlying management performance make use of a variety of variables at different levels of analysis. A framework is presented in which variables of three different types are linked together. Using data from a sample (n = 437) of British managers this article explores relationships between personality factors (using the big-five factors), work competencies and managerial performance. Results from the analyses reveal a set of underlying competency factors, which show different patterns of correlation with two facets of performance: current proficiency and promotability. In turn, these factors and the facets of performance show relationships with the big-five personality factors. Current proficiency is more closely related to competencies of organization, specialization and analysis – competencies more likely to be displayed by people who are conscientious and introverted. Promotability is linked more closely to competencies concerning action/motivation, flexibility/sensitivity and communication – competencies more likely to be displayed by people who are extroverted with lower conscientiousness and agreeableness.     

Social work in South Africa at the dawn of the new millennium

The article examines recent developments in social policy and its implications for social work education and practice in South Africa. It traces the changes from the birth of democracy in South Africa to the dawn of the new millennium as these crucial years marked the beginning of a new era in South Africa's welfare history. It examines the challenges to social work and provides an example of the integrated, holistic developmental interventions, which are needed to combat social problems such as crime, AIDS and poverty. It ends with an examination of the implications of developmental welfare policy for social–work education as social workers are called to address mass poverty, unemployment and social deprivation through greater use of diverse social work methods, such as advocacy, community development, empowerment, consultation, networking, action research and policy analysis.