The Witch-Hunt Metaphor (And Accusations against Residential Care Workers)

Correspondence to Mr Chris Beckett, Anglia Polytechnic University, School of Community Health and Social Studies, Cambridge CB1 1PT, UK. Summary This Critical Commentary examines the widespread use of themetaphor of the witchhunt in relation to child sexual abuseinvestigations when they are perceived as being unjustified.The use of this metaphor can be seen to be part of a backlash,part of a widespread desire to discredit the evidence that sexualabuse is widespread. However, it is argued here that the metaphoris actually quite apt in the case of the recent wave of convictionsof residential care workers, where the methods used have beenquite suspect—and genuinely reminiscent in some respectsof those used in historic witch hunts. It is suggested thatlegitimate child protection will ultimately be the loser ifthis is not addressed.     

Solutions for a class of invex programming problems

A nonconvex constrained optimization problem is considered in which the constraints are of the form of generalized polynomials. An invexity kernel is established for this class of problem, and a consequent theorem gives sufficient conditions for the solutions of such problems.     

Improved bootstrap confidence intervals in certain toxicological experiments

The bootstrap, the jackknife, and classical methods are compared through their confidence intervals for the proportion of affected fetuses in a common type of animal experiment. Specifically, suppose that for the ith of M pregnant animals, there are x _i affected fetuses out of n _i total in the litter. The conditional distribution of x _i given n _i is sometimes modeled as binomial (n _i p _i ), where p _i is a realization from some unknown continuous density. The p _i are not observable and it is of interest in some toxicological experiments to find confidence intervals for E(p). Theory suggests that the proposed parametric bootstrap should produce higher order agreement between the nominal and actual coverage than that exhibited by the usual nonparametric bootstrap. Some simulation results provide additional evidence of this superiority of the modified parametric bootstrap over the jack-knife and classical approaches. The proposed resampling is flexible enough to handle a more general model allowing correlation between p _i and n _i .     

On Testing Sample Selection Bias Under the Multicollinearity Problem

ABSTRACT

This paper reviews and extends the literature on the finite sample behavior of tests for sample selection bias. Monte Carlo results show that, when the “multicollinearity problem” identified by Nawata (1993 Nawata , K. ( 1993 ). A note on the estimation of models with sample-selection biases . Economics Letters 42 : 15 – 24 . [CSA] [CROSSREF] [Crossref], [Web of Science ®] , [Google Scholar]) is severe, (i) the t-test based on the Heckman–Greene variance estimator can be unreliable, (ii) the Likelihood Ratio test remains powerful, and (iii) nonnormality can be interpreted as severe sample selection bias by Maximum Likelihood methods, leading to negative Wald statistics. We also confirm previous findings (Leung and Yu, 1996 Leung , S. F. , Yu , S. ( 1996 ). On the choice between sample selection and two-part models . Journal of Econometrics 72 : 197 – 229 . [CSA] [CROSSREF] [Crossref], [Web of Science ®] , [Google Scholar]) that the standard regression-based t-test (Heckman, 1979 Heckman , J. J. ( 1979 ). Sample selection bias as a specification error . Econometrica 47 : 153 – 161 . [CSA] [Crossref], [Web of Science ®] , [Google Scholar]) and the asymptotically efficient Lagrange Multiplier test (Melino, 1982 Melino , A. ( 1982 ). Testing for sample selection bias . Review of Economic Studies 49 : 151 – 153 . [CSA] [Crossref], [Web of Science ®] , [Google Scholar]), are robust to nonnormality but have very little power.     

A Generalization of Gurland's Theorem,with Applications to Economic Behavior under Uncertainty

We illustrate the use of the Mathematica software system (programming language) for performing Bayesian calculations of the sort encountered in introductory presentations of Bayesian statistics. In particular, we show the ease with which one can do numerical computation, graphics, and symbolic computation to analyze one- and two-dimensional probability density functions. Our illustrations involve a time series problem using oxygen uptake data taken from a burn patient.     

A Tale of Two Matrix Factorizations

In statistical practice, rectangular tables of numeric data are commonplace, and are often analyzed using dimension-reduction methods like the singular value decomposition and its close cousin, principal component analysis (PCA). This analysis produces score and loading matrices representing the rows and the columns of the original table and these matrices may be used for both prediction purposes and to gain structural understanding of the data. In some tables, the data entries are necessarily nonnegative (apart, perhaps, from some small random noise), and so the matrix factors meant to represent them should arguably also contain only nonnegative elements. This thinking, and the desire for parsimony, underlies such techniques as rotating factors in a search for “simple structure.” These attempts to transform score or loading matrices of mixed sign into nonnegative, parsimonious forms are, however, indirect and at best imperfect. The recent development of nonnegative matrix factorization, or NMF, is an attractive alternative. Rather than attempt to transform a loading or score matrix of mixed signs into one with only nonnegative elements, it directly seeks matrix factors containing only nonnegative elements. The resulting factorization often leads to substantial improvements in interpretability of the factors. We illustrate this potential by synthetic examples and a real dataset. The question of exactly when NMF is effective is not fully resolved, but some indicators of its domain of success are given. It is pointed out that the NMF factors can be used in much the same way as those coming from PCA for such tasks as ordination, clustering, and prediction. Supplementary materials for this article are available online.     

Effects of community violence exposure and parental mental health on the internalizing problems of urban adolescents

Previous research has documented an association between adolescent community violence exposure (CVE) and poor psychological functioning. The purpose of this study is to delineate the relations of CVE, parental mental health, and adolescent PTSD and depression. Participants consisted of 121 pairs of junior high and high school students and their parents. Adolescents completed measures to assess their history of violence exposure and current psychological functioning. Parents completed a demographic questionnaire and measures assessing their psychological functioning. Hierarchical regression analyses were conducted, and results indicated that, after controlling for demographic variables and family violence exposure, parental mental health emerged as a moderating variable in the relation between CVE and adolescent-rated PTSD, but not in the association between adolescent CVE and depression. Clinical implications of this study and directions for future research are discussed.     

A meta-analytic framework to adjust for bias in external control studies

While randomized controlled trials (RCTs) are the gold standard for estimating treatment effects in medical research, there is increasing use of and interest in using real-world data for drug development. One such use case is the construction of external control arms for evaluation of efficacy in single-arm trials, particularly in cases where randomization is either infeasible or unethical. However, it is well known that treated patients in non-randomized studies may not be comparable to control patients—on either measured or unmeasured variables—and that the underlying population differences between the two groups may result in biased treatment effect estimates as well as increased variability in estimation. To address these challenges for analyses of time-to-event outcomes, we developed a meta-analytic framework that uses historical reference studies to adjust a log hazard ratio estimate in a new external control study for its additional bias and variability. The set of historical studies is formed by constructing external control arms for historical RCTs, and a meta-analysis compares the trial controls to the external control arms. Importantly, a prospective external control study can be performed independently of the meta-analysis using standard causal inference techniques for observational data. We illustrate our approach with a simulation study and an empirical example based on reference studies for advanced non-small cell lung cancer. In our empirical analysis, external control patients had lower survival than trial controls (hazard ratio: 0.907), but our methodology is able to correct for this bias. An implementation of our approach is available in the R package ecmeta .     

Behavioural problems of adolescents in secure residential youth care: Gender differences and risk factors

Adolescents in secure residential care mostly suffer from serious behavioural problems, often accompanied by trauma and adverse family circumstances. This paper presents findings of a comparison of behavioural problems and risk factors of 255 boys and girls (aged 12 to 18 years) in secure residential care in the Netherlands and their association with behavioural problems. A cross-sectional design and standardized questionnaires were used to measure behavioural problems and individual and familial risk factors. By using independent-sample t tests, the severity of these factors in boys and girls was compared, and by using structural equation modelling (SEM), associations between these factors and behavioural problems were investigated. The findings of the study show that post-traumatic stress disorder (PTSD) symptoms, maladaptive emotion regulation, impaired perceived competence and internalizing behavioural problems were more severe in girls than in boys. Boys experienced more severe externalizing behavioural problems and more family problems than girls. Maladaptive emotion regulation, PTSD symptoms, perceived competence and parenting problems were related to behavioural problems. The results indicate that treatment for girls should address PTSD symptoms, perceived competence and maladaptive emotion regulation and that extra attention for family problems in the treatment of boys is warranted.     

Electronic Markets for Truckload Transportation

A wide variety of electronic marketplace formats are used in the Truckload (TL) transportation industry, including combinatorial auctions, private and public exchanges, and electronic catalogs. Combinatorial multi‐attribute auctions are commonly used strategically to populate electronic catalogs, commonly called “routing guides,” with pricing, assignments, and priority logic. Private and public exchanges are used to complement the electronic catalogs in cases where the catalog fails. This paper discusses the TL transportation market, places the procurement of services in the context of electronic marketplace formats, and illustrates how these are currently used.