Assessing accuracy of a continuous screening test in the presence of verification bias

Summary.  In studies to assess the accuracy of a screening test, often definitive disease assessment is too invasive or expensive to be ascertained on all the study subjects. Although it may be more ethical or cost effective to ascertain the true disease status with a higher rate in study subjects where the screening test or additional information is suggestive of disease, estimates of accuracy can be biased in a study with such a design. This bias is known as verification bias. Verification bias correction methods that accommodate screening tests with binary or ordinal responses have been developed; however, no verification bias correction methods exist for tests with continuous results. We propose and compare imputation and reweighting bias-corrected estimators of true and false positive rates, receiver operating characteristic curves and area under the receiver operating characteristic curve for continuous tests. Distribution theory and simulation studies are used to compare the proposed estimators with respect to bias, relative efficiency and robustness to model misspecification. The bias correction estimators proposed are applied to data from a study of screening tests for neonatal hearing loss.     

Improving performance? The adoption and implementation of quality systems in U.K. nonprofits

There are increasing and multiple pressures on nonprofit organizations to demonstrate excellence in performance. Although there is a growing literature on the various approaches to performance improvement taken by nonprofits, little is known about the processes involved in the adoption and implementation of specific approaches. This article is about the adoption and use of one approach to performance improvement, “quality systems,” in the U.K. nonprofit sector. We report findings about factors that encourage nonprofits to adopt quality systems. We also analyze the distinctive challenges of implementing quality approaches in a nonprofit sector context and suggest critical success factors. The article concludes with a discussion of the organizational and policy implications of applying the management concepts of quality and performance to the nonprofit sector.     

Community versus development? Land use and development policy in Vermont as a tool toward community viability

This paper examines Vermont's Land Use and Development Law (Act250) as a means of promoting community development through publicpolicy. Central to the law are mechanisms that invite citizenparticipation in the development and planning process. Accordingly,citizens can organize and undertake collective action againstdevelopment projects that are understood as posing a threatto the ongoing life of the community. A case is explored inwhich citizens organized under the banner of Act 250 to preventWal-Mart from entering their community, in order to protecta vulnerable downtown area that had centred public and commerciallife for generations.     

Natural and social order at Walt Disney World; the functions and contradictions of civilising nature

Elias’ theory of the civilising process is used to show how the Walt Disney World Theme Parks construct social control over visitors without calling into question the official presentation of these visitors as free, choice‐making, experience seeking individuals. Particular attention is drawn to the manipulation of images of nature as either ‘wild’ or ‘civilised’ to code, respectively, forbidden and legitimate places for visitors. In doing so, WDW is able to maintain civilised, non‐coercive, discourse with its ‘guests’ who are, thus presented to themselves as responsible and self‐regulating persons. Attention is drawn to the contradiction that this strategy creates between ‘authentic’ and ‘civilised’ spectacle particularly in the presentation of animals. It is noted how this creates an imperative to show only civilised animal behaviour but which, in turn, limits the means that the Disney Corporation can adopt in order to create a space that is free from the intrusion of uncivilised nature.     

Child‐Care Usage and Mother‐Infant “Quality Time”

Mothers' time‐use patterns were compared in families in which infants spent more than 30 hours per week in child care (In‐Care group; n= 143) versus 0 hours per week (At‐Home group; n= 183) from birth to 6 months of age. In‐Care group mothers spent about 12 fewer hours per week interacting with their infants, for about 32% less time; fathers of these infants were more involved in caregiving. The groups did not differ in the quality of mother‐infant interaction. In the In‐Care group, quantity of interaction was related to greater separation anxiety and concerns about effects of maternal employment. Time‐use data were not related to child outcomes at 15 months of age. Results suggest that the effect of extensive time spent apart on the quantity and quality of mother‐infant interaction may be smaller than anticipated.     

Children's involvement in their parents' divorce: implications for practice

The paper reports findings from a research study that explored children's experience of divorce. It shows that children experience parental divorce as a crisis in their lives but that they are able to mobilise internal and external resources to regain a new point of balance. In doing so, children demonstrate the degree to which they are active and competent participants in the process of family dissolution. The implications of the data are then considered in relation to engaging with children involved in divorce and in relation to some of the cultural presumptions that might militate against hearing what they have to say about their experiences. Copyright © 2002 John Wiley & Sons, Ltd.     

ELICITING A DIRECTED ACYCLIC GRAPH FOR A MULTIVARIATE TIME SERIES OF VEHICLE COUNTS IN A TRAFFIC NETWORK

The problem of modelling multivariate time series of vehicle counts in traffic networks is considered. It is proposed to use a model called the linear multiregression dynamic model (LMDM). The LMDM is a multivariate Bayesian dynamic model which uses any conditional independence and causal structure across the time series to break down the complex multivariate model into simpler univariate dynamic linear models. The conditional independence and causal structure in the time series can be represented by a directed acyclic graph (DAG). The DAG not only gives a useful pictorial representation of the multivariate structure, but it is also used to build the LMDM. Therefore, eliciting a DAG which gives a realistic representation of the series is a crucial part of the modelling process. A DAG is elicited for the multivariate time series of hourly vehicle counts at the junction of three major roads in the UK. A flow diagram is introduced to give a pictorial representation of the possible vehicle routes through the network. It is shown how this flow diagram, together with a map of the network, can suggest a DAG for the time series suitable for use with an LMDM.     

Loss functions for estimation of extrema with an application to disease mapping

It is often of interest to find the maximum or near maxima among a set of vector‐valued parameters in a statistical model; in the case of disease mapping, for example, these correspond to relative‐risk “hotspots” where public‐health intervention may be needed. The general problem is one of estimating nonlinear functions of the ensemble of relative risks, but biased estimates result if posterior means are simply substituted into these nonlinear functions. The authors obtain better estimates of extrema from a new, weighted ranks squared error loss function. The derivation of these Bayes estimators assumes a hidden‐Markov random‐field model for relative risks, and their behaviour is illustrated with real and simulated data.