Illicit use of prescribed stimulant medication among college students

The authors investigated illicit use of stimulant medications at a midwestern university. They used a questionnaire to (a) examine the extent to which university students illicitly used stimulant medications prescribed for attention-deficit hyperactivity disorder; (b) determine why college students abused such drugs; and (c) identify the factors that predicted illicit use of prescribed stimulant medication. Findings revealed that 17% of 179 surveyed men and 11% of 202 women reported illicit use of prescribed stimulant medication. Forty-four percent of surveyed students stated that they knew students who used stimulant medication illicitly for both academic and recreational reasons. Students reported they experienced time pressures associated with college life and that stimulants were said to increase alertness and energy. Regression analysis revealed that the factor that predicted men's use was knowing where to get easily acquired stimulant medication, whereas the main predictor for women was whether another student had offered the prescribed stimulants.     

Organizational Linkages and Resource Mobilization: The Significance of Linkage Strength and Breadth*

This paper discusses the importance of identifying the environmental context in which organizations function. The relationship between an organization and those other groups and individuals constituting its environment is specified in terms of linkages. Two key dimensions of linkage are identified: strength and breadth. The former refers to how intimately the organization is connected with any other group while the latter refers to how extensive is the support. These linkages' dimensions are viewed from a “resource mobilization” perspective, i.e., as the means by which resources are brought into an organization. A study of linkages sustained by the NAACP during 1961–69 illustrates how the dimensions of linkage strength and breadth can be operationalized and applied. New avenues of research then are suggested.     

Packing <Emphasis Type="Bold">[1, Δ]</Emphasis>-factors in graphs of small degree

Given an undirected, connected graph G with maximum degree Δ, we introduce the concept of a [1, Δ]-factor k-packing in G, defined as a set of k edge-disjoint subgraphs of G such that every vertex of G has an incident edge in at least one subgraph. The problem of deciding whether a graph admits a [1,Δ]-factor k-packing is shown to be solvable in linear time for k = 2, but NP-complete for all k≥ 3. For k = 2, the optimisation problem of minimising the total number of edges of the subgraphs of the packing is NP-hard even when restricted to subcubic planar graphs, but can in general be approximated within a factor of by reduction to the Maximum 2-Edge-Colorable Subgraph problem. Finally, we discuss implications of the obtained results for the problem of fault-tolerant guarding of a grid, which provides the main motivation for research.     

Likelihood estimation for exchangeable multinomial data

In this article, maximum likelihood estimates of an exchangeable multinomial distribution using a parametric form to model the parameters as functions of covariates are derived. The non linearity of the exchangeable multinomial distribution and the parametric model make direct application of Newton Rahpson and Fisher's scoring algorithms computationally infeasible. Instead parameter estimates are obtained as solutions to an iterative weighted least-squares algorithm. A completely monotonic parametric form is proposed for defining the marginal probabilities that results in a valid probability model.     

On the measurement and analysis of asymmetry with applications to facial modelling

Summary.  Asymmetry is a feature of shape which is of particular interest in a variety of applications. With landmark data, the essential information on asymmetry is contained in the degree to which there is a mismatch between a landmark configuration and its relabelled and matched reflection. This idea is explored in the context of a study of facial shape in infants, where particular interest lies in identifying changes over time and in assessing residual deformity in children who have had corrective surgery for a cleft lip or cleft lip and palate. Interest lies not in whether the mean shape is asymmetric but in comparing the degrees of asymmetry in different populations. A decomposition of the asymmetry score into components that are attributable to particular features of the face is proposed. A further decomposition allows different sources of asymmetry due to position, orientation or intrinsic asymmetry to be identified for each feature. The methods are also extended to data representing anatomical curves across the face.     

Detecting discontinuities in nonparametric regression curves and surfaces

The existence of a discontinuity in a regression function can be inferred by comparing regression estimates based on the data lying on different sides of a point of interest. This idea has been used in earlier research by Hall and Titterington (1992), Müller (1992) and later authors. The use of nonparametric regression allows this to be done without assuming linear or other parametric forms for the continuous part of the underlying regression function. The focus of the present paper is on assessing the evidence for the presence of a discontinuity within a regression function through examination of the standardised differences of ‘left’ and ‘right’ estimators at a variety of covariate values. The calculations for the test are carried out through distributional results on quadratic forms. A graphical method in the form of a reference band to highlight the sources of the evidence for discontinuities is proposed. The methods are also developed for the two covariate case where there are additional issues associated with the presence of a jump location curve. Methods for estimating this curve are also developed. All the techniques, for the one and two covariate situations, are illustrated through applications.     

Does poor weight gain identify children in need?

To determine the socioeconomic variables in children with slow growth (failure to thrive), a case–control study was carried out in two economically deprived areas of Newcastle upon Tyne. Three hundred and six children, aged 12–24 months, registered at two health authority clinics, were studied by reviewing their growth charts. Sixty-three had poor growth (weight deviating downwards across two major centiles from the maximum centile attained at 4–8 weeks of age). Five children were excluded because of known organic disease. A matched control group of normally growing children was selected from the same clinics. Study children and controls were examined and their parents interviewed on a range of socioeconomic, health and interactional factors. A health visitor assessment and a record of social work contact was obtained. The slowly growing children differed significantly from controls in being lighter and shorter, while their mothers spent less on food, needed more help with the child, had a poorer home environment and expressed greater concern over their child's health. Four different patterns of poor growth were identified by inspection of the charts: early onset (before 6 months but sustained), late onset (after 6 months), temporary and recurrent. The ‘recurrent’ group was associated with parenting difficulties and the ‘late onset’ group with adverse socioeconomic factors. Slow growth patterns in children under 2 years may be used as a screening tool to identify ‘children in need’ and should be sought on a population basis. Those identified can then be assessed further to ascertain the area where underlying difficulties lie, for intervention to follow as appropriate.