Showing papers on "Reliability (statistics) published in 2012"

Interrater reliability: the kappa statistic

Abstract: The kappa statistic is frequently used to test interrater reliability. The importance of rater reliability lies in the fact that it represents the extent to which the data collected in the study are correct representations of the variables measured. Measurement of the extent to which data collectors (raters) assign the same score to the same variable is called interrater reliability. While there have been a variety of methods to measure interrater reliability, traditionally it was measured as percent agreement, calculated as the number of agreement scores divided by the total number of scores. In 1960, Jacob Cohen critiqued use of percent agreement due to its inability to account for chance agreement. He introduced the Cohen's kappa, developed to account for the possibility that raters actually guess on at least some variables due to uncertainty. Like most correlation statistics, the kappa can range from -1 to +1. While the kappa is one of the most commonly used statistics to test interrater reliability, it has limitations. Judgments about what level of kappa should be acceptable for health research are questioned. Cohen's suggested interpretation may be too lenient for health related studies because it implies that a score as low as 0.41 might be acceptable. Kappa and percent agreement are compared, and levels for both kappa and percent agreement that should be demanded in healthcare studies are suggested.

Reviewing studies with diverse designs: the development and evaluation of a new tool

Abstract: Rationale, aims & objective Tools for the assessment of the quality of research studies tend to be specific to a particular research design (e.g. randomized controlled trials, or qualitative interviews).This makes it difficult to assess the quality of a body of research that addresses the same or a similar research question but using different approaches. The aim of this paper is to describe the development and preliminary evaluation of a quality assessment tool that can be applied to a methodologically diverse set of research articles. Methods The 16-item quality assessment tool (QATSDD) was assessed to determine its reliability and validity when used by health services researchers in the disciplines of psychology, sociology and nursing. Qualitative feedback was also gathered from mixedmethods health researchers regarding the comprehension, content, perceived value and usability of the tool. Results Reference to existing widely used quality assessment tools and experts in systematic review confirmed that the components of the tool represented the construct of ‘good research technique’ being assessed. Face validity was subsequently established through feedback from a sample of nine health researchers. Inter-rater reliability was established through substantial agreement between three reviewers when applying the tool to a set of three research papers ( k= 71.5%), and good to substantial agreement between their scores at time 1 and after a 6-week interval at time 2 confirmed test‐retest reliability. Conclusions The QATSDD shows good reliability and validity for use in the quality assessment of a diversity of studies, and may be an extremely useful tool for reviewers to standardize and increase the rigour of their assessments in reviews of the published papers which include qualitative and quantitative work.

Introduction to Structural Equation Modeling Using IBM SPSS Statistics and Amos

Abstract: PART ONE: PREPARING YOURSELF AND YOUR DATA Introduction Measuring Your Variables: Reliability and Validity Factor Analysis PART TWO: THE THREE BASIC MODELS Structural Equation Modeling with AMOS Models with Only Manifest Variables The Measurement Model in SEM: Confirmatory Factor Analysis The General Model PART THREE: ADVANCED MODELS AND TECHNIQUES Mean Structures and Multi-Group Analysis Incomplete and Non-Normal Data Latent Curve Models

The Monte Carlo Simulation Method for System Reliability and Risk Analysis

Abstract: Monte Carlo simulation is one of the best tools for performing realistic analysis of complex systems as it allows most of the limiting assumptions on system behavior to be relaxed. The Monte Carlo Simulation Method for System Reliability and Risk Analysis comprehensively illustrates the Monte Carlo simulation method and its application to reliability and system engineering. Readers are given a sound understanding of the fundamentals of Monte Carlo sampling and simulation and its application for realistic system modeling.Whilst many of the topics rely on a high-level understanding of calculus, probability and statistics, simple academic examples will be provided in support to the explanation of the theoretical foundations to facilitate comprehension of the subject matter. Case studies will be introduced to provide the practical value of the most advanced techniques. This detailed approach makes The Monte Carlo Simulation Method for System Reliability and Risk Analysis a key reference for senior undergraduate and graduate students as well as researchers and practitioners. It provides a powerful tool for all those involved in system analysis for reliability, maintenance and risk evaluations.

Value of Travel Time Reliability: A Review of Current Evidence

Abstract: Travel time reliability is a fundamental factor in travel behavior. It represents the temporal uncertainty experienced by users in their movement between any two nodes in a network. The importance of the time reliability depends on the penalties incurred by the users. In road networks, travelers consider the existence of a trip travel time uncertainty in different choice situations (departure time, route, mode, and others). In this paper, a systematic review of the current state of research in travel time reliability, and more explicitly in the value of travel time reliability is presented. Moreover, a meta-analysis is performed in order to determine the reasons behind the discrepancy among the reliability estimates.

Value of Travel Time Reliability: A review of current evidence.

Abstract: Travel time reliability is a fundamental factor in travel behavior. It represents the temporal uncertainty experienced by travelers in their movement between any two nodes in a network. The importance of the time reliability depends on the penalties incurred by the travelers. In road networks, travelers consider the existence of a trip travel time uncertainty in different choice situations (departure time, route, mode, and others). In this paper, a systematic review of the current state of research in travel time reliability, and more explicitly in the value of travel time reliability is presented. Moreover, a meta-analysis is performed in order to determine the reasons behind the discrepancy among the reliability estimates.

Real-time numerical forecast of global epidemic spreading: case study of 2009 A/H1N1pdm

Abstract: Background Mathematical and computational models for infectious diseases are increasingly used to support public-health decisions; however, their reliability is currently under debate. Real-time forecasts of epidemic spread using data-driven models have been hindered by the technical challenges posed by parameter estimation and validation. Data gathered for the 2009 H1N1 influenza crisis represent an unprecedented opportunity to validate real-time model predictions and define the main success criteria for different approaches.

Reconfiguration of Power Distribution Systems Considering Reliability and Power Loss

Abstract: A power distribution system reconfiguration methodology considering the reliability and the power loss is developed in this paper. Probabilistic reliability models are used in order to evaluate the reliability at the load points. An algorithm for finding the minimal cut sets is utilized to find the minimal set of components appearing between the feeder and any particular load point. The optimal status of the switches in order to maximize the reliability and minimize the real power loss is found by a binary particle swarm optimization-based search algorithm. The effectiveness of the proposed methodology is demonstrated on a 33-bus and a 123-bus radial distribution system.

Impact of Performance-Based Contracting on Product Reliability: An Empirical Analysis

Abstract: Using a proprietary data set provided by a major manufacturer of aircraft engines, we empirically investigate how product reliability is impacted by the use of two different types of after-sales maintenance support contracts: time and material contracts (T&MC) and performance-based contracts (PBC). We offer a number of competing arguments based on the theory of incentives that establish why product reliability may increase or decrease under PBC. We build a two-stage econometric model that explicitly accounts for the endogeneity of contract choices, and find evidence of a positive and significant effect of PBC on product reliability. The estimation of our model indicates that product reliability is higher by 25%--40% under PBC compared to under T&MC, once the endogeneity of contract choice is taken into account. Our results are consistent with two mechanisms for reliability improvement under PBC: more frequent scheduled maintenance and better care performed in each maintenance event. This paper was accepted by Martin Lariviere, operations management.

The reliability and concurrent validity of shoulder mobility measurements using a digital inclinometer and goniometer: a technical report.

Abstract: Purpose/Aim: This study investigated the intrarater reliability and concurrent validity of active shoulder mobility measurements using a digital inclinometer and goniometer.

Replication Analysis in Exploratory Factor Analysis: What it is and why it makes your analysis better

Abstract: Copyright is retained by the first or sole author, who grants right of first publication to the Practical Assessment, Research & Evaluation. Permission is granted to distribute this article for nonprofit, educational purposes if it is copied in its entirety and the journal is credited. PARE has the right to authorize third party reproduction of this article in print, electronic and database forms.

Uncertainty modelling and limit state reliability of tunnel supports under seismic effects

Abstract: Underground openings and excavations are increasingly being used for civilian and strategic purposes all over the world. Recent earthquakes and resulting damage have brought into focus and raised the awareness for aseismic design and construction. In addition, underground tunnels, particularly, have distinct seismic behaviour due to their complete enclosure in soil or rock and their significant length. Therefore, seismic response of tunnel support systems warrant closer attention. The geological settings in which they are placed are often difficult to describe due to limited site investigation data and vast spatial variability. Therefore, the parameters which govern the design are many and their variabilities cannot be ignored. A solution to this issue is reliability based analysis and design. These real conditions of variability can only be addressed through a reliability based design. The problem addressed here is one of reliability-based analysis of the support system of an underground tunnel in soil. Issues like the description of the interaction between the tunnel lining and the surrounding medium, the type of limit state that would be appropriate, the nonavailability of a closed form performance function and the advantages of response surface method [RSM] are looked into. Both static and seismic environment with random variability in the material properties are studied here. Support seismic response is studied in terms of thrust, moment and shear forces in the lining. Interactive analysis using finite element method [FEM], combined with RSM and Hasofer-Lind reliability concept to assess the performance of the tunnel support, has proven useful under real field situations.

Assessment of Interprofessional Team Collaboration Scale (AITCS): development and testing of the instrument

Abstract: Methods: The AITCS, with its 47 items within 4 subscales (partnership, cooperation, coordination, and shared decision making) and assessed on a 5-point Likert scale, was administered to a total of 125 practitioners from 7 health care teams practicing within a variety of settings, in 2 provinces in Canada. Results: Principal components and factor analysis of data resulted in 37 items loading onto 3 factors, explaining 61.02% of the variance. The internal consistency estimates for reliability of each subscale ranged from 0.80 to 0.97, with an overall reliability of 0.98. Thus, the AITCS is a reliable and valid instrument. Discussion: The psychometric analysis of this instrument supports its value in measuring collaboration within teams and when patients are included as team members. The AITCS can be applied to continuing professional education interventions to determine change over time. It has limitations to the Canadian context and within the settings where participants practiced. Further test and retest reliability and longitudinal study application is needed.

Reliability Assessment of Smart Grid Considering Direct Cyber-Power Interdependencies

Abstract: Smart grid initiatives are becoming more and more achievable through the use of information infrastructures that feature peer-to-peer communication, monitoring, protection and automated control. The analysis of smart grid operation requires considering the reliability of the cyber network as it is neither invulnerable nor failure free. This paper quantitatively evaluates the reliability of modern power systems, which incorporates the impact of cyber network failures on the reliability of the power network. In this paper, four types of interdependencies are defined and a new concept of state mapping is proposed to map the failures in the cyber network to the failures of the power network. Furthermore, in order to evaluate the impact of direct cyber-power interdependencies on the reliability indices, two optimization models are introduced to maximize the data connection in the cyber network and minimize the load shedding in the power network. The effectiveness of proposed reliability evaluation method is shown by a smart microgrid application. The methodology presented in this paper is a start point to optimize the future power grid which has increasingly interdependencies between cyber and power networks.

Reliability, Maintainability and Risk

Abstract: Reliability, maintainability and risk , Reliability, maintainability and risk , کتابخانه دیجیتال جندی شاپور اهواز

A Nested Extreme Response Surface Approach for Time-Dependent Reliability-Based Design Optimization

Abstract: A primary concern in practical engineering design is ensuring high system reliability throughout a product's lifecycle, which is subject to time-variant operating conditions and component deteriorations. Thus, the capability of dealing with time-dependent probabilistic constraints in reliability-based design optimization (RBDO) is of vital importance in practical engineering design applications. This paper presents a nested extreme response surface (NERS) approach to efficiently carry out time-dependent reliability analysis and determine the optimal designs. This approach employs the kriging model to build a nested response surface of time corresponding to the extreme value of the limit state function. The efficient global optimization (EGO) technique is integrated with the NERS approach to extract the extreme time responses of the limit state function for any given system design. An adaptive response prediction and model maturation (ARPMM) mechanism is developed based on the mean square error (MSE) to concurrently improve the accuracy and computational efficiency of the proposed approach. With the nested response surface of time, the time-dependent reliability analysis can be converted into the time-independent reliability analysis, and existing advanced reliability analysis and design methods can be used. The NERS approach is compared with existing time-dependent reliability analysis approaches and integrated with RBDO for engineered system design with time-dependent probabilistic constraints. Two case studies are used to demonstrate the efficacy of the proposed NERS approach.

Reliability Evaluation of Active Distribution Systems Including Microgrids

Abstract: This paper proposes a new method for reliability evaluation of active distribution systems with multiple microgrids based on a Monte Carlo simulation. Multi-state models are developed on the basis of generalized capacity outage tables (GCOTs) to better represent various types of distributed generators in reliability evaluation. Then, the virtual power plant (VPP) is introduced to model microgrids with intermittent sources. Furthermore, the reliability behavior of VPP is efficiently characterized by an equivalent GCOT. The nonsequential Monte Carlo method is then adopted to evaluate the reliability of active distribution systems considering different operation modes under single or multiple contingencies. Some techniques-such as two-step state sampling, zone partitioning and minimal path search-are proposed to facilitate the state evaluation process and improve the Monte Carlo simulation speed. The effectiveness and efficiency of the proposed method are validated through extensive numerical tests on an IEEE test system and a real-life active distribution network.

Reliability and Availability of Cloud Computing

Abstract: A holistic approach to service reliability and availability of cloud computingReliability and Availability of Cloud Computing provides IS/IT system and solution architects, developers, and engineers with the knowledge needed to assess the impact of virtualization and cloud computing on service reliability and availability. It reveals how to select the most appropriate design for reliability diligence to assure that user expectations are met.Organized in three parts (basics, risk analysis, and recommendations), this resource is accessible to readers of diverse backgrounds and experience levels. Numerous examples and more than 100 figures throughout the book help readers visualize problems to better understand the topicand the authors present risks and options in bulleted lists that can be applied directly to specific applications/problems.Special features of this book include:Rigorous analysis of the reliability and availability risks that are inherent in cloud computingSimple formulas that explain the quantitative aspects of reliability and availabilityEnlightening discussions of the ways in which virtualized applications and cloud deployments differ from traditional system implementations and deploymentsSpecific recommendations for developing reliable virtualized applications and cloud-based solutionsReliability and Availability of Cloud Computing is the guide for IS/IT staff in business, government, academia, and non-governmental organizations who are moving their applications to the cloud. It is also an important reference for professionals in technical sales, product management, and quality management, as well as software and quality engineers looking to broaden their expertise.

Aplicabilidad de los criterios de rigor y éticos en la investigación cualitativa

Abstract: The purpose of this paper is to reflect on how to guarantee quality in a qualitative study. The criteria of rigor and ethics that need to be considered in research pursuant to this model are highlighted as basic concepts. Reliability and validity, and the respective criteria that allow for their verification, also are described. Details are provided on some of the ethical elements that require careful oversight during the research process and contribute to quality and scientific rigor. In conclusion, the article cites the criteria of rigor and ethics, and their respective interrelationship, as fundamental pillars in evaluating research intended to explore subjective aspects of human nature.

Reliability Evaluation of Grid-Connected Photovoltaic Power Systems

Abstract: This study presents a systematic way to evaluate reliability performance of large grid-connected photovoltaic (PV) power systems considering variation of input power and ambient-condition-dependent failure rates of critical components including PV modules, inverters, and capacitors. State enumeration is used to analyze real-life grid-connected PV systems. Ambient-condition-dependent failure rates of major components in PV systems are formulated and incorporated in reliability analysis. A series of reliability indices are defined to quantify PV systems' reliability performance. In addition, sensitivity analyses are extensively conducted to investigate the impact of different factors on the performances of PV power systems. Test results on a practical 20-kW PV project are presented to demonstrate the effectiveness of the proposed method.

Software self-checking systems and methods

Abstract: Software self-checking mechanisms are described for improving software tamper resistance and/or reliability. Redundant tests are performed to detect modifications to a program while it is running. Modifications are recorded or reported. Embodiments of the software self-checking mechanisms can be implemented such that they are relatively stealthy and robust, and so that it they are compatible with copy-specific static watermarking and other tamper-resistance techniques.

What sample sizes for reliability and validity studies in neurology

Abstract: Rating scales are increasingly used in neurologic research and trials. A key question relating to their use across the range of neurologic diseases, both common and rare, is what sample sizes provide meaningful estimates of reliability and validity. Here, we address two questions: (1) to what extent does sample size influence the stability of reliability and validity estimates; and (2) to what extent does sample size influence the inferences made from reliability and validity testing? We examined data from two studies. In Study 1, we retrospectively reduced the total sample randomly and nonrandomly by decrements of approximately 50 % to generate sub-samples from n = 713-20. In Study 2, we prospectively generated sub-samples from n = 20-320, by entry time into study. In all samples we estimated reliability (internal consistency, item total correlations, test-retest) and validity (within scale correlations, convergent and discriminant construct validity). Reliability estimates were stable in magnitude and interpretation in all sub-samples of both studies. Validity estimates were stable in samples of n ≥ 80, for 75 % of scales in samples of n = 40, and for 50 % of scales in samples of n = 20. In this study, sample sizes of a minimum of 20 for reliability and 80 for validity provided estimates highly representative of the main study samples. These findings should be considered provisional and more work is needed to determine if these estimates are generalisable, consistent, and useful.