Digital Module 16: Longitudinal Data Analysis

In this digital ITEMS module, Dr. Jeffrey Harring and Ms. Tessa Johnson introduce the linear mixed effects (LME) model as a flexible general framework for simultaneously modeling continuous repeated measures data with a scientifically defensible function that adequately summarizes both individual change as well as the average response. The module begins with a nontechnical overview of longitudinal data analyses drawing distinctions with cross-sectional analyses in terms of research questions to be addressed. Nuances of longitudinal designs, timing of measurements, and the real possibility of missing data are then discussed. The three interconnected components of the LME model—(1) a model for individual and mean response profiles, (2) a model to characterize the covariation among the time-specific residuals, and (3) a set of models that summarize the extent that individual coefficients vary—are discussed in the context of the set of activities comprising an analysis. Finally, they demonstrate how to estimate the linear mixed effects model within an open-source environment (R). The digital module contains sample R code, diagnostic quiz questions, hands-on activities in R, curated resources, and a glossary.     

Predicting ground reaction forces in running using micro-sensors and neural networks

Measurement of ground reaction force (GRF) in running provides a direct indication of the loads to which the body is subjected at each foot-ground contact, and can provide an objective explanation for performance outcomes. Traditionally, the collection of three orthogonal component GRF data in running requires an athlete to complete a series of return loops along a laboratory based runway, within which a force platform is embedded, in order to collect data from a discrete footfall. The major disadvantages associated with this GRF data collection methodology include the inability to assess multiple consecutive foot contacts and the fact that measurements are typically confined to the laboratory. The objective of this research was to investigate the potential for wearable instrumentation to be employed, in conjunction with artificial neural network (ANN) and multiple linear regression (MLR) models, for the estimation of GRF in middle distance running. A modular wearable data acquisition system was developed to acquire in-shoe force (ISF) data. Matched data sets from wearable instrumentation (source data) and force plate (target data) records were collected from elite middle-distance runners under controlled laboratory conditions for the purposes of ANN and MLR model development (MD) and model validation (MV). In terms of statistical measures of prediction accuracy the MLR model was found to provide a superior level of accuracy for the prediction of the vertical and medio-lateral components of GRF and alternatively, the ANN model provided the most accurate predictions of the anterior-posterior component of GRF. The prediction accuracy of each component of GRF was found to be governed by the inherent signal variability, in which case the vertical and anterior-posterior components were more reliable and subsequently predicted significantly more accurately than the medio-lateral component. The emerging capability for obtaining continuous GRF records from wearable instrumentation has the potential to permit unprecedented quantification of training stress and competition demands in running.     

国内外优秀男子跳远运动员部分技术指标差异性分析

对国内外优秀跳远运动员和世界顶级跳远运动员的助跑速度利用率、短程和全程助跑跳远成绩差、K值三项指标进行对比分析,发现我国优秀男子跳远运动员助跑速度利用率明显高于世界顶级选手,但技术评定等级低于世界顶级选手,主要原因是起跳环节存在差距。不同运动员最佳的助跑速度利用率存在差别,高助跑速度利用率需要有与之相对应的起跳能力和跑跳结合能力。     

大型体育赛事风险评估指标研究现状

对大型体育赛事的概念、组织、风险的定义进行概述,综述大型体育赛事风险评估指标的研究现状,并列举了实例.     

运动员高原训练返回平原训练血象指标的变化观察

探讨运动员高原训练之后返回平原训练的血象指标变化规律。方法:取10名广西自由式摔跤男子运动员高原训练之后返回平原训练的不同时段(第3、14、28、35天),分别测试红细胞计数(RBC)、血红蛋白(HB)、红细胞压积(HCT)、白细胞(WBC)及分类、血小板(PLT)等18项血象指标。结果:RBC、HB、HCT在不同时段出现不同的变化,其中第3天至14天是逐渐下降的过程,14天形成一个低谷,28天回升到高峰,第35天又呈下降趋势,差异有统计学意义(P<0.01)。WBC及分类、血小板等指标也有一定的规律性变化,但无统计学意义。结论:运动员高原训练之后返回平原训练的不同时间血象指标的变化有一定规律性,对评定高原训练的效果及运动员机能状态和体能的恢复情况的准确判断有着重要意义。     

Home advantage in speed skating: Evidence from individual data

Home advantage is a well-documented phenomenon in many sports. Home advantage has been shown to exist for team sports (soccer, hockey, football, baseball, basketball) and for countries organizing sports tournaments like the Olympics and World Cup Soccer. There is also some evidence for home advantage in some individual sports, but there is a much more limited literature. This paper addresses the issue of home advantage in speed skating. From a methodological point of view, it is difficult to identify home advantage, because skaters vary in their abilities and the conditions of tournaments vary. There is a small but significant home advantage using a generalized linear mixed model, with random effects for skaters and fixed effects for skating rinks and seasons. Even though the home advantage effect exists, it is very small when compared to variation in skating times due to differences of rinks and individual abilities.     

关于排列的几种类型

排列组合内容抽象,富于技巧;它的思想方法也别具一格,知识间的联系,主要靠抽象思维来把握.它的解题技巧更是多种多样,灵活多变.有鉴于此,对排列问题进行详细分类,对于正确理解排列概念,进而准确进行排列数的计算是大有裨益的.列举了各种不同类型的排列,归纳总结了不同类型排列的计数公式.并通过典型例题的分析与解答,介绍解题的思想方法,给出解答各类题目的具体规律,并提供一些常用的解题技能和技巧.     

线性代数课程教学的探索与实践——以数学证明教育价值实现的课堂教学为例

要教好线性代数课程,其核心问题就是要通过课堂教学,使学生理解相关的数学知识;训练和培养学生的思维能力以及数学交流能力;帮助学生寻找新旧知识之间的内在联系,使知识系统化;在巩固已有知识的基础上,让学生自己去发现新知识.要实现这一教学目标,训练学生掌握"数学证明"的概念和在实践中的应用至关重要.传统的做法往往是通过"定义一引理一证明一定理一证明一推论"这种复杂的、程序化方法来进行训练的.由于在初等代数课程中,学生很少接受严格数学证明的训练,所以这种俗套的做法成效甚微.相反,如果把线性代数的主题和概念用一种完全合理的探究式方法来引入,那么数学证明的概念和架构将牢固植根于学生的头脑,并且这种思维习惯将对他们后续课程的学习和掌握公理化推理方法都会有很大帮助.     

试论耕地占用与GDP增长的脱钩研究副标题用

我国人均耕地资源匮乏,耕地占用压力十分巨大,为深入分析和认识耕地占用与GDP增长的关系,可以应用Decoupling(脱钩)理论与分析方法,开展我国耕地占用与GDP增长的脱钩研究。其主要思路是在全面分析、对比和总结国内外不同GDP增长阶段耕地保护政策的基础上,建立基于DPR(驱动力-压力-响应)系统的耕地占用与GDP增长之间的脱钩指标体系,应用脱钩指标分析耕地占用和GDP增长之间的相互关系,在此基础上通过DPR(GDP增长驱动力-耕地占用压力-政策响应)系统,建立耕地占用与GDP增长脱钩的新型管理制度,最后应用上述框架模式,分别按省、地、县三级选取一些典型区域进行同尺度之间的实证分析,并进行跟踪分析,以验证耕地占用与GDP增长脱钩指标及相应的管理制度和政策的实施效果,揭示我国各类区域耕地占用与GDP增长的相互关系的典型模式,提升耕地保护研究 的理论水平与促进我国的耕地保护工作。     

基于BSC的ERP系统实施绩效评价研究

通过对传统ERP绩效评价理论和方法的对比分析,提出基于BSC的ERP系统实施绩效评价方法.在对企业战略目标与ERP系统目标的因果关系分析基础之上,建立基于BSC的ERP系统绩效评价模型,并为ERP平衡计分卡建立关键绩效指标体系,希望能对ERP系统的实施效果从业务流程、客户、财务以及学习与创新四个角度进行全面而又综合的评价.