Exploratory semiparametric analysis of two-dimensional diffusions in finance

We examine bivariate extensions of Aït-Sahalia’s approach to the estimation of univariate diffusions. Our message is that extending his idea to a bivariate setting is not straightforward. In higher dimensions, as opposed to the univariate case, the elements of the Itô and Fokker-Planck representations do not coincide; and, even imposing sensible assumptions on the marginal drifts and volatilities is not sufficient to obtain direct generalisations. We develop exploratory estimation and testing procedures, by parametrizing the drifts of both component processes and setting restrictions on the terms of either the Itô or the Fokker-Planck covariance matrices. This may lead to highly nonlinear ordinary differential equations, where the definition of boundary conditions is crucial. For the methods developed, the Fokker-Planck representation seems more tractable than the Itô’s. Questions for further research include the design of regularity conditions on the time series dependence in the data, the kernels actually used and the bandwidths, to obtain asymptotic properties for the estimators proposed. A particular case seems promising: “causal bivariate models” in which only one of the diffusions contributes to the volatility of the other. Hedging strategies which estimate separately the univariate diffusions at stake may thus be improved.

Bullying among adolescents in a sub-Saharan middle-income setting.

PURPOSE: This study explored factors associated with self-reported bullying among adolescents in a sub-Saharan country. METHODS: A cross-sectional sample of adolescents (n = 1,427) in the Seychelles was drawn from the Global School-based Student Health Survey. Bullied adolescents were compared with non-bullied adolescents with respect to several sociodemographic factors. Bivariate and multivariate analyses were performed. RESULTS: Within a 30 day period, 38.8% of adolescents reported being bullied. Bullied youths were more likely to be depressed (adjusted odds ratio [aOR] = 1.63; confidence intervals [CI] = 1.27-1.07) and socially deprived (aOR = 1.85; CI = 1.30-2.61). Being older (aOR = .83; CI = .77-.90) and having close friends (aOR = .53; CI = .31-.91) were protective factors. CONCLUSIONS: The prevalence of bullying in the Seychelles is high, and social correlates are similar to those in industrialized settings. More research is needed to examine bullying patterns outside the school environment.

A bivariate regression model for matched paired survival data: local influence and residual analysis

The use of bivariate distributions plays a fundamental role in survival and reliability studies. In this paper, we consider a location scale model for bivariate survival times based on the proposal of a copula to model the dependence of bivariate survival data. For the proposed model, we consider inferential procedures based on maximum likelihood. Gains in efficiency from bivariate models are also examined in the censored data setting. For different parameter settings, sample sizes and censoring percentages, various simulation studies are performed and compared to the performance of the bivariate regression model for matched paired survival data. Sensitivity analysis methods such as local and total influence are presented and derived under three perturbation schemes. The martingale marginal and the deviance marginal residual measures are used to check the adequacy of the model. Furthermore, we propose a new measure which we call modified deviance component residual. The methodology in the paper is illustrated on a lifetime data set for kidney patients.

Middle managers' attitudes toward employee assistance programs in the corporate setting

Several studies have shown that successful Employee Assistance Programs (EAPs) have strong management endorsement. Strong management endorsement is defined as positive support in utilizing EAP services for themselves and their employees. This study focuses solely on middle management as opposed to upper or general management support. The study further examines success or lack of success of an EAP by the utilization rate defined as the number of employees over a year period who access EAP services.^ A analytical cross-sectional design was used to compare and observe differences between two groups of middle managers (utilizers and nonutilizers). Middle manager data was collected through a mail questionnaire. The study focused on identifying predictors that influence middle managers' utilization rate specifically: attitude toward EAPs, EAP knowledge level, attitude toward mental health professionals, age, gender, years worked as a middle manager, education level, training, and other possible predictors of utilization. The overall hypothesis states middle manager utilizers of EAP services have more positive attitudes and a better understanding of their EAP than middle management nonutilizers.^ As predicted, nonparametric bivariate results showed significant differences between the two groups. Middle managers in the utilization group (n = 473) tended to show more positive attitudes toward their EAP and mental health professionals and demonstrated greater EAP knowledge compared to the nonutilization group (n = 154). These findings support past studies on variables that influence EAP utilization rates.^ Further variables found to influence middle management utilization were identified by multivariate logistic regression results. These variable were gender (female supervisors), educational levels of employees supervised (employees with lower levels of education), number of employees supervised (greater the number supervised, more likely to utilize), managerial EAP training (trained supervisors) and awareness that problems do influence an employee's productivity.^ These findings strengthen the assertion that middle management's attitudes, as well as other variables may influence utilization. Study findings add new information about important variables specifically influencing middle management who utilize EAPs. An understanding of these variables is essential in developing competent EAP program training and orientation programs for middle managers. ^

Economic preferences in the health setting. Three case studies concerning the needs of breast cancer patients, pain management in oncology and extreme end-of-life decisions

The thesis describes three studies concerning the role of the Economic Preference set investigated in the Global Preference Survey (GPS) in the following cases: 1) the needs of women with breast cancer; 2) pain undertreament in oncology; 3) legal status of euthanasia and assisted suicide. The analyses, based on regression techniques, were always conducted on the basis of aggregate data and revealed in all cases a possible role of the Economic Preferences studied, also resisting the concomitant effect of the other covariates that were considered from time to time. Regarding individual studies, the related conclusion are: 1) Economic Preferences appear to play a role in influencing the needs of women with breast cancer, albeit of non-trivial interpretation, statistically "resisting" the concomitant effect of the other independent variables considered. However, these results should be considered preliminary and need further confirmation, possibly with prospective studies conducted at the level of the individual; 2) the results show a good degree of internal consistency with regard to pro-social GPS scores, since they are all found to be non-statistically significant and united, albeit only weakly in trend, by a negative correlation with the % of pain undertreated patients. Sharper, at least statistically, is the role of Patience and Willingness to Take Risk, although of more complex empirical interpretation. 3) the results seem to indicate an obvious role of Economic Preferences, however difficult to interpret empirically. Less evidence, at least on the inferential level, emerged, however, regarding variables that, based on common sense, should play an even more obvious role than Economic Preferences in orienting attitudes toward euthanasia and assisted suicide, namely Healthcare System, Legal Origin, and Kinship Tightness; striking, in particular, is the inability to prove a role for the dominant religious orientation even with a simple bivariate analysis.

Evaluation of the Incidence of Bladder Perforation After Transurethral Bladder Tumor Resection in a Residency Setting

Purpose: To evaluate prospectively the actual bladder perforation incidence during transurethral resection of bladder tumor (TURB) performed by residents and to identify possible predisposing factors to such condition. Patients and Methods: Thirty-four patients with bladder tumor were submitted to TURB in our academic institution in April 2006, and were prospectively studied. Procedures were all done by senior residents under an attending direct supervision. All patients had a cystograms performed after the procedure by the injection of 400 mL of saline-diluted contrast solution with low-pressure infusion through the Foley catheter. The cystograms were evaluated blindly by a single radiologist. All patients were examined by cystoscopy and/or CT every 3 months for the first 2 years postoperatively. Results: The cystogram showed contrast leaking compatible with bladder perforation in 17 (50%) cases. None of the perforations were recognized intraoperatively by the surgeon. All perforations were extraperitoneal and managed conservatively. There was no significant correlation between the incidence of bladder perforation and the patient age (p = 0.508), the tumor stage (p = 0.998), the tumor grade (p = 0.833), the number of lesions (p = 0.394), and the tumor size (p = 0.651). The only factor that had impact on the development of bladder perforation was tumor localization at the bottom of the bladder (p = 0.035; OR, 6750; 95% CI, 1.14, 39.8). Conclusion: Asymptomatic perforations of the bladder wall occur very frequently after a TURB procedure performed by residents in training and, most of the time, are not noticed by the surgeon. Localization of the tumor at bladder dome was the only factor that negatively influenced perforation rates.

Additive genetic relationship of longevity with fertility and production traits in Nellore cattle based on bivariate models

Survival or longevity is an economically important trait in beef cattle. The main inconvenience for its inclusion in selection criteria is delayed recording of phenotypic data and the high computational demand for including survival in proportional hazard models. Thus, identification of a longevity-correlated trait that could be recorded early in life would be very useful for selection purposes. We estimated the genetic relationship of survival with productive and reproductive traits in Nellore cattle, including weaning weight (WW), post-weaning growth (PWG), muscularity (MUSC), scrotal circumference at 18 months (SC18), and heifer pregnancy (HP). Survival was measured in discrete time intervals and modeled through a sequential threshold model. Five independent bivariate Bayesian analyses were performed, accounting for cow survival and the five productive and reproductive traits. Posterior mean estimates for heritability (standard deviation in parentheses) were 0.55 (0.01) for WW, 0.25 (0.01) for PWG, 0.23 (0.01) for MUSC, and 0.48 (0.01) for SC18. The posterior mean estimates (95% confidence interval in parentheses) for the genetic correlation with survival were 0.16 (0.13-0.19), 0.30 (0.25-0.34), 0.31 (0.25-0.36), 0.07 (0.02-0.12), and 0.82 (0.78-0.86) for WW, PWG, MUSC, SC18, and HP, respectively. Based on the high genetic correlation and heritability (0.54) posterior mean estimates for HP, the expected progeny difference for HP can be used to select bulls for longevity, as well as for post-weaning gain and muscle score.

Charles Darwin goes to school: the role of cartoons and narrative in setting science in an historical context

Science education is under revision. Recent changes in society require changes in education to respond to new demands. Scientific literacy can be considered a new goal of science education and the epistemological gap between natural sciences and literacy disciplines must be overcome. The history of science is a possible bridge to link these `two cultures` and to foster an interdisciplinary approach in the classroom. This paper acknowledges Darwin`s legacy and proposes the use of cartoons and narrative expositions to put this interesting chapter of science into its historical context. A five-lesson didactic sequence was developed to tell part of the story of Darwin`s expedition through South America for students from 10 to 12 years of age. Beyond geological and biological perspectives, the inclusion of historical, social and geographical facts demonstrated the beauty and complexity of the findings that Darwin employed to propose the theory of evolution.

Control charts for individual observations of a bivariate Poisson process

In this paper, three single-control charts are proposed to monitor individual observations of a bivariate Poisson process. The specified false-alarm risk, their control limits, and ARLs were determined to compare their performances for different types and sizes of shifts. In most of the cases, the single charts presented better performance rather than two separate control charts ( one for each quality characteristic). A numerical example illustrates the proposed control charts.

Adult language input in the early childhood educational setting

Age-related changes in the adult language addressed to children aged 2;0-4;0 years in polyadic conditions were investigated in Australian childcare centres. The language that 21 staff members addressed to these children was coded for multiple variables in the broad social categories of prosody, context, speech act and gesture. The linguistic components were coded within the categories of phonology, lexicon, morphology, syntax and referential deixis. Minimal age-related differences were found. Explanations for the similarity of the adult language input across the age groups within the early childhood educational environment, will be discussed

Parameter setting and statistical learning

Three main models of parameter setting have been proposed: the Variational model proposed by Yang (2002; 2004), the Structured Acquisition model endorsed by Baker (2001; 2005), and the Very Early Parameter Setting (VEPS) model advanced by Wexler (1998). The VEPS model contends that parameters are set early. The Variational model supposes that children employ statistical learning mechanisms to decide among competing parameter values, so this model anticipates delays in parameter setting when critical input is sparse, and gradual setting of parameters. On the Structured Acquisition model, delays occur because parameters form a hierarchy, with higher-level parameters set before lower-level parameters. Assuming that children freely choose the initial value, children sometimes will miss-set parameters. However when that happens, the input is expected to trigger a precipitous rise in one parameter value and a corresponding decline in the other value. We will point to the kind of child language data that is needed in order to adjudicate among these competing models.