Mixed-effects models for health care longitudinal data with an informative visiting process: A Monte Carlo simulation study

Electronic health records are being increasingly used in medical research to answer more relevant and detailed clinical questions; however, they pose new and significant methodological challenges. For instance, observation times are likely correlated with the underlying disease severity: Patients with worse conditions utilise health care more and may have worse biomarker values recorded. Traditional methods for analysing longitudinal data assume independence between observation times and disease severity; yet, with health care data, such assumptions unlikely hold. Through Monte Carlo simulation, we compare different analytical approaches proposed to account for an informative visiting process to assess whether they lead to unbiased results. Furthermore, we formalise a joint model for the observation process and the longitudinal outcome within an extended joint modelling framework. We illustrate our results using data from a pragmatic trial on enhanced care for individuals with chronic kidney disease, and we introduce user-friendly software that can be used to fit the joint model for the observation process and a longitudinal outcome.     

体育教育生态环境优化思考

运用生态学的理论与方法审视体育教学环境的构成特征,分析体育教育系统中教学内容、方法、课程设置和教师等和环境要素对教学的影响,提出以体育文化与实践课程相结合,教学资源与现代教学方法手段相结合优化体育教学生态化环境,以创新教育理念营造动态发展的体育生态环境。     

TRIVARIATE SUPPORT OF FLAT‐VOLATILITY FORWARD LIBOR RATES

This paper investigates the multivariate support of forward Libor rates in the one‐factor, constant volatilities Libor market model. The comparatively simple bivariate case was solved in Jamshidian (2008) in connection to the recent finding by Davis and Mataix‐Pastor (2007) of positive probability of negative Libor rates in the swap market model. The approach here builds on Jamshidian (2008) but becomes really effective only in the trivariate case, and there particularly for a special “flat‐volatility” case, leading to an analytic solution. The main idea is a certain recursion in the Libor market model by means of which the calculation of the support is reduced to a calculus of variation problem (with bounds on the slope).     

面向就业的创业教育模式优化路径探析——基于高职院校创业教育的过程调研

依托高职院校创业教育实践过程开展研究,通过焦点组访谈和大样本调研并借助结构方程模型(Structural Equation Modeling,SEM),在创业教育的时间自主性、地点仿真性和学生对创业教育的就业价值认知及其参与创业教育意愿等方面建立多元回归模型,根据对创业教育过程数据的监测分析,为高职院校面向就业的创业教育模式调整实施提供依据。     

运用价值工程理论优化中职校本教研立项工作

在中职校本教研立项工作当中运用价值工程理论,通过开展价值分析辅助完成课题论证,有助于提高中职校本教研课题立项的针对性、适用性和可操作性,实现优化中职校本教研立项工作、提高教研项目应用水平和经济效益的目的。     

FAST MONTE CARLO GREEKS FOR FINANCIAL PRODUCTS WITH DISCONTINUOUS PAY‐OFFS

We introduce a new class of numerical schemes for discretizing processes driven by Brownian motions. These allow the rapid computation of sensitivities of discontinuous integrals using pathwise methods even when the underlying densities postdiscretization are singular. The two new methods presented in this paper allow Greeks for financial products with trigger features to be computed in the LIBOR market model with similar speed to that obtained by using the adjoint method for continuous pay‐offs. The methods are generic with the main constraint being that the discontinuities at each step must be determined by a one‐dimensional function: the proxy constraint. They are also generic with the sole interaction between the integrand and the scheme being the specification of this constraint.     

Assessing the impact of taxes on female labor supply using a finite mixture approach

This paper expands the standard analysis of female labor supply to permit preference heterogeneity by using a finite mixture model. Using the extended model, we obtain theory consistent results whereas a traditional model produces a negative substitution effect. We use our model to illustrate the labor supply effects of a tax reform, corresponding to 1983–1992 changes in the Swedish income-tax schedule. The results shows an expected reduction in tax revenues of about 17%. Finally, we use Monte Carlo simulations and show that our proposed mixture model is robust towards different misspecifications. First version received: March 1998/final version accepted: October 1999     

Cardinality versus q-norm constraints for index tracking

Index tracking aims at replicating a given benchmark with a smaller number of its constituents. Different quantitative models can be set up to determine the optimal index replicating portfolio. In this paper, we propose an alternative based on imposing a constraint on the q-norm (0?<?q?<?1) of the replicating portfolios’ asset weights: the q-norm constraint regularises the problem and identifies a sparse model. Both approaches are challenging from an optimization viewpoint due to either the presence of the cardinality constraint or a non-convex constraint on the q-norm. The problem can become even more complex when non-convex distance measures or other real-world constraints are considered. We employ a hybrid heuristic as a flexible tool to tackle both optimization problems. The empirical analysis of real-world financial data allows us to compare the two index tracking approaches. Moreover, we propose a strategy to determine the optimal number of constituents and the corresponding optimal portfolio asset weights.     

Relationships of Perceived Justice to Service Recovery,Service Failure Attributions,Recovery Satisfaction,and Loyalty in the Context of Airline Travelers

In recent years, hospitality and tourism researchers have presented their findings of many studies on website performance and evaluations. Although these prior studies have achieved a certain degree of success for assisting industrial practitioners to develop and maintain their websites, it remains largely unknown how consumers find a specific travel or hotel website. This paper reports a study that investigated the perceived importance of different channels for finding travel or hotel websites from an international travelers' perspective. Empirical results from 153 travel or hotel website users indicated that the Google search engine was the only channel that was perceived as important, and 47.4% of the respondents viewed up to three screens in the list of search results when using search engines. The paper should be of interest to industrial practitioners and academic researchers to understand better the behavior of users of travel and hotel websites during their website search procedure.     

High-dimensional Hawkes processes for limit order books: modelling,empirical analysis and numerical calibration

High-dimensional Hawkes processes with exponential kernels are used to describe limit order books in order-driven financial markets. The dependencies between orders of various types are carefully studied and modelled, based on a thorough empirical analysis. The observation of inhibition effects is particularly interesting, and leads us to the use of non-linear Hawkes processes. Specific attention is devoted to the calibration problem, in order to account for the high dimensionality of the problem and the very poor convexity properties of the MLE. Our analyses show a good agreement between the statistical properties of order book data and those of the model.