Estimation of bivariate excess probabilities for elliptical models

Let $(X,Y)$ be a random vector whose conditional excess probability $\theta(x,y):=P(Y\leq y | X>x)$ is of interest. Estimating this kind of probability is a delicate problem as soon as $x$ tends to be large, since the conditioning event becomes an extreme set. Assume that $(X,Y)$ is elliptically distributed, with a rapidly varying radial component. In this paper, three statistical procedures are proposed to estimate $\theta(x,y)$ for fixed $x,y$, with $x$ large. They respectively make use of an approximation result of Abdous et al. (cf. Canad. J. Statist. 33 (2005) 317--334, Theorem 1), a new second order refinement of Abdous et al.'s Theorem 1, and a non-approximating method. The estimation of the conditional quantile function $\theta(x,\cdot)^{\leftarrow}$ for large fixed $x$ is also addressed and these methods are compared via simulations. An illustration in the financial context is also given.Comment: Published in at http://dx.doi.org/10.3150/08-BEJ140 the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

An adaptation index to high summer heat associated with adverse health impacts in deprived neighborhoods

Socially and materially disadvantaged urban areas present a group of factors strongly correlated with high heat and humidity adverse health effects, particularly in densely populated cities where the heat island effect extends over large areas. This paper presents an adaptation index to high summer heat whose validity was tested by correlating it with self-reported adverse health impacts to heat. The data comes from a 2011 cross-sectional study conducted in the most deprived areas in 9 cities of 100,000 or more inhabitants in Quebec (Canada). In total, 3,485 people were interviewed at home. An index of various behavioral adaptations was developed using a Multiple Correspondence Analysis. This individual-level adaptation index summarizes a range of 14 easy-to-use and energy-efficient solutions for cooling off or protecting oneself against the sun, both at home and in other places, whether indoors or out. In addition, it shows that adaptation to heat goes beyond air conditioning in the home. People who experience adverse effects of heat on their health tend to adopt more of the behaviors measured by the index than those perceiving little or none, regardless of their age group or presence of air conditioning at home. Monitoring and improving this index over time and in several populations and contexts would establish a significant milestone for adaptation in health promotion and prevention

The role of exopolysaccharides from a chromate reducing Pseudomonas aeruginosa in resistance to hexavalent chromium and antibiotics

زمینه و هدف: کروم شش ظرفیتی (VI) یکی از اکسید کننده های بسیار قوی و جز عناصر سرطان زای گروه A است که در پساب صنایع مختلف وجود دارد. اگزو پلی ساکاریدهای (EPS) ترشح شده توسط باکتری های موجود در این پساب ها می تواند نقش موثری در افزایش مقاومت باکتری ها به این عامل نامساعد ایفا نماید. این تحقیق با هدف بررسی نقش EPS باکتری های مقاوم به کرومات در احیای کروم VI و مقاومت آنتی بیوتیکی آن ها صورت گرفته است. روش بررسی: این مطالعه مقطعی- آزمایشگاهی بر روی باکتری های مقاوم به کرومات موجود در انواع مختلف پساب صورت گرفت. حداکثر غلظت قابل تحمل کرومات (MTC)، مقدار ترشح EPS، احیای کرومات توسط EPS و مقاومت آنتی بیوتیکی جدایه انتخابی به روش کیربی- بائر تعیین گردید. یافته ها: جدایه موثر که واجد بالاترین MTC ( mM128) و حداکثر توان ترشح EPS ( mg.ml-1117/0) بود، بر اساس نتایج تست های بیوشیمیایی گونه ای از سودوموناس آئروژینوزا تشخیص داده شد. مقایسه راندمان 61 درصدی احیای کرومات توسط EPS با راندمان 78 درصدی احیای سلولی کرومات حاکی از نقش قابل توجه EPS در احیای کرومات بود. این باکتری به طیف وسیعی از آنتی بیوتیک ها نیز مقاومت نشان داد. نتیجه گیری: افزایش کروم VI در محیط منجر به افزایش مقاومت باکتری ها با به کارگیری انواع مکانیسم های سازشی چون افزایش ترشح EPS می گردد و به موازات آن مقاومت آنتی بیوتیکی نیز افزایش می یابد. این مقاومت توام از لحاظ پزشکی بسیار مهم بوده و می تواند اطلاعات ارزشمندی در ارتباط با مکانیسم مقاومت آنتی بیوتیکی، ژنتیک پلاسمید و اکولوژی جدایه مورد نظر در اختیار ما قرار دهد

On semiparametric regression for count explanatory variables

International audienceWe study the problem of semiparametric estimation of a multivariate count regression function m : Nd -> R that can be represented as a product of an unknown discrete parametric function r and an unknown discrete smooth function w. For the construction of such estimators, we first find an approximation result br for the parametric part r, and then estimate the nonparametric multiplicative correction factor w = m/br by a discrete associated-kernel method. Comparisons are therefore carried out with the nonparametric count regression estimator of Nadaraya-Watson type. We point out that the new semiparametric count regression estimator can reduce the bias with respect to purely nonparametric count regression estimator, without affecting the variance

On the residual dependence index of elliptical distributions

The residual dependence index of bivariate Gaussian distributions is determined by the correlation coefficient. This tail index is of certain statistical importance when extremes and related rare events of bivariate samples with asymptotic independent components are being modeled. In this paper we calculate the partial residual dependence indices of a multivariate elliptical random vector assuming that the associated random radius is in the Gumbel max-domain of attraction. Furthermore, we discuss the estimation of these indices when the associated random radius possesses a Weibull-tail distribution.Comment: 11 pages, case \theta=1 now include

Estimation of conditional laws given an extreme component

Let $(X,Y)$ be a bivariate random vector. The estimation of a probability of the form $P(Y\leq y \mid X >t)$ is challenging when $t$ is large, and a fruitful approach consists in studying, if it exists, the limiting conditional distribution of the random vector $(X,Y)$, suitably normalized, given that $X$ is large. There already exists a wide literature on bivariate models for which this limiting distribution exists. In this paper, a statistical analysis of this problem is done. Estimators of the limiting distribution (which is assumed to exist) and the normalizing functions are provided, as well as an estimator of the conditional quantile function when the conditioning event is extreme. Consistency of the estimators is proved and a functional central limit theorem for the estimator of the limiting distribution is obtained. The small sample behavior of the estimator of the conditional quantile function is illustrated through simulations.Comment: 32 pages, 5 figur

Well Begun is Half Done: Using Online Orientation to Foster Online Students\u27 Academic Self-Efficacy

Past research suggests that the use of an online learning orientation is an effective proactive strategy to ease online students\u27 transition into online learning. Based on a sample of 3,888 online students from an urban public university, we used ordinal logistic regression to understand the influence of students\u27 satisfaction with an online learning orientation (OLO), their prior level of online learning experience, and their demographics on their academic self-efficacy (ASE). Consistent with prior research, our findings confirmed the influence of students\u27 satisfaction with OLO, their prior online learning experience, and their gender on their ASE. Unsatisfied students were 85% less likely than satisfied students to express a high level of self-efficacy. In contrast, students\u27 age and enrollment status proved not to be significant. Overall, our findings provide strong evidence about how the use of an OLO as proactive support strategy can boost online students\u27 academic self-efficacy

Implementing an Enterprise Information System to Reengineer and Streamline Administrative Processes in a Distance Learning Unit

During the past three years, we have developed and implemented an enterprise information system (EIS) to reengineer and facilitate the administrative process for preparing and teaching distance learning courses in a midsized-to-large university (with 23,000 students). The outcome of the implementation has been a streamlined and efficient process which has delivered higher faculty satisfaction at a substantial cost reduction. In this paper, we propose a new conceptual and operational framework for process reengineering (PR) in higher education institutions. We also share our practical experience gained while designing, developing, and integrating three subsystems into an EIS. We hope that our experience, delineated in this paper, will help other universities’ distance learning efforts and will encourage them to implement enterprise information systems to effectively manage their administrative processes

Wage losses in the year after breast cancer: Extent and determinants among Canadian women

This article is available open access through the publisher’s website at the link below. © The Author 2008.Background - Wage losses after breast cancer may result in considerable financial burden. Their assessment is made more urgent because more women now participate in the workforce and because breast cancer is managed using multiple treatment modalities that could lead to long work absences. We evaluated wage losses, their determinants, and the associations between wage losses and changes for the worse in the family's financial situation among Canadian women over the first 12 months after diagnosis of early breast cancer. Methods - We conducted a prospective cohort study among women with breast cancer from eight hospitals throughout the province of Quebec. Information that permitted the calculation of wage losses and information on potential determinants of wage losses were collected by three pretested telephone interviews conducted over the year following the start of treatment. Information on medical characteristics was obtained from medical records. The main outcome was the proportion of annual wages lost because of breast cancer. Multivariable analysis of variance using the general linear model was used to identify personal, medical, and employment characteristics associated with the proportion of wages lost. All statistical tests were two-sided. Results - Among 962 eligible breast cancer patients, 800 completed all three interviews. Of these, 459 had a paying job during the month before diagnosis. On average, these working women lost 27% of their projected usual annual wages (median = 19%) after compensation received had been taken into account. Multivariable analysis showed that a higher percentage of lost wages was statistically significantly associated with a lower level of education (Ptrend = .0018), living 50 km or more from the hospital where surgery was performed (P = .070), lower social support (P = .012), having invasive disease (P = .086), receipt of chemotherapy (P < .001), self-employment (P < .001), shorter tenure in the job (Ptrend < .001), and part-time work (P < .001). Conclusion - Wage losses and their effects on financial situation constitute an important adverse consequence of breast cancer in Canada.The Canadian Breast Cancer Research Alliance, Canadian Institutes of Health Research, and Fondation de l’Université Laval