A REVIEW OF BOUNDS FOR THE EFFICIENCY FACTOR OF BLOCK DESIGNS

This paper draws together bounds for the efficiency factor of block designs, starting with the papers of Conniffe & Stone (1974) and Williams & Patterson (1977). By extending the methods of Jarrett (1983), firstly to cover supercomplete block designs and then to cover resolvable designs, a set of bounds is obtained which provides the best current bounds for any block design with equal replication and equal block size, including resolvable designs and two-replicate resolvable designs as special cases. The bounds given for non-resolvable designs apply strictly only to designs which are either regular-graph (John & Mitchell, 1977) or whose duals are regular-graph. It is conjectured (John & Williams, 1982) that they are in fact global bounds. Similar qualifications apply to the bounds for resolvable designs.     

HIV/AIDS and homelessness

This article describes the results of research on the demographic, housing, psychosocial characteristics, and service needs of a sample of homeless people with HIV disease. Results show that respondents are similar in demographic and housing characteristics to the general homeless population. On average, respondents report high levels of stress and depression, moderate satisfaction with perceived social support availability, moderate beliefs in their ability to influence health related outcomes, moderate levels of self-efficacy, and low levels of physical and psychosocial disability. A range of services was identified as both helpful and useful in supporting a stable living arrangement. Implications for social policy, service provision, and research are discussed.     

Sociologists,social policy and the Estranged poor: The selective inattention to the limits of success

Current antipoverty initiatives have been given impetus by the rediscovery of an “underclass”—a social category widely considered to be a distinctive subset of the poor. In the ensuing discussion, this aggregate has been related the Estranged Poor after Hochschild (1989). Social interventions granted the imprimatur of success are most frequently presented and/or interpreted as if they are applicable to all of the poor. It is argued here that this is an unwarranted exaggeration of effectiveness. The concept of a helping mismatch is introduced suggesting an intrinsic lack of articulation between formal agents of social intervention and the Estranged Poor who are therefore bypassed by even the most successful programs. Strains to exaggeration are described and explained as consequences of structural aspects of the remedial action system. Sociologists involved in social intervention have largely ignored the selectivity of success and too often prescribed directions for remedial action, which are irrelevant to the Estranged Poor. To acknowledge the limits of success can only encourage a more rational pursuit of our humanistic goals through the development of different approaches and strategies and, not incidentally, contribute to the credibility of our profession.     

Absentéisme et productivité: le cas des enseignants aux Etats‐Unis

Partant de données relatives à 285 professeurs et 8 631 élèves d'un district scolaire économiquement désavantagé des Etats‐Unis, les auteurs testent l'hypothèse selon laquelle les absences des enseignants sont souvent discrétionnaires et réduisent leur productivité, mesurée par les résultats des élèves à un examen de mathématiques. Comme cela est courant, lorsque le remplaçant est moins qualifié, l'enseignement est moins intense et cohérent, avec une chute, limitée mais significative, des résultats des élèves, pouvant conduire à une baisse de leur classification et de leur motivation. Les auteurs proposent des mesures susceptibles de limiter cet absentéisme.     

Random field models in image analysis*

Image models are useful in quantitatively specifying natural constraints and general assumptions about the physical world and the imaging process. This review paper explains how Gibbs and Markov random field models provide a unifying theme for many contemporary problems in image analysis. Random field models permit the introduction of spatial context into pixel labeling problems, such as segmentation and restoration. Random field models also describe textured images and lead to algorithms for generating textured images, classifying textures and segmenting textured images. In spite of some impressive model-based image restoration and texture segmentation results reported in the literature, a number of fundamental issues remain unexplored, such as the specification of MRF models, modeling noise processes, performance evaluation, parameter estimation, the phase transition phenomenon and the comparative analysis of alternative procedures. The literature of random field models is filled with great promise, but a better mathematical understanding of these issues is needed as well as efficient algorithms for applications. These issues need to be resolved before random field models will be widely accepted as general tools in the image-processing community.