Related Reliability Measures Research Articles

On the modified Burr IV model for hydrological events: development, properties, characterizations and applications

We introduce a new distribution for modeling extreme events about frequency analysis called modified Burr IV (MBIV) distribution. We derive the MBIV distribution on the basis of the generalized Pearson differential equation. The proposed model turns out to be flexible: its density function can be symmetrical, right-skewed, left-skewed, J and bimodal shaped. Its hazard rate has shapes such as bathtub and modified bathtub, increasing, decreasing, and increasing-decreasing-increasing. To show the importance of the MBIV distribution, we establish various mathematical properties such as random number generator, sub-models, moments related properties, inequality measures, reliability measures, uncertainty measures and characterizations. We utilize the maximum likelihood estimation technique to estimate the model parameters. We assess the behavior of the maximum likelihood estimators (MLEs) of the MBIV parameters via a simulation study. Five data sets related to frequency analysis are considered to elucidate the significance of the MBIV distribution. We show that the MBIV model is the best model to analyze data for hydrological events, motivating its high level of adaptability in the applied setting.

Test-retest reliability and minimal detectable change of the Balance Evaluation Systems Test and its two abbreviated versions in persons with mild to moderate spinocerebellar ataxia: A pilot study.

BACKGROUND:The reliability of the evaluation of the Balance Evaluation Systems Test (BESTest) and its two abbreviated versions are confirmed for balance characteristics and reliability. However, they are not utilized in cases of spinocerebellar ataxia (SCA).OBJECTIVE:We aimed to examine the test-retest reliability and minimal detectable change (MDC) of the BESTest and its abbreviated versions in persons with mild to moderate spinocerebellar ataxia.METHODS:The BESTest was performed in 20 persons with SCA at baseline and one month later. The scores of the abbreviated version of the BESTest were determined from the BESTest scores. The interclass correlation coefficient (1,1) was used as a measure of relative reliability. Furthermore, we calculated the MDC in the BESTest and its abbreviated versions.RESULTS:The intraclass correlation coefficients (1,1) and MDC at 95% confidence intervals were 0.92, 8.7(8.1%), 0.91, 4.1(14.5%), and 0.81, 5.2(21.6%) for the Balance, Mini-Balance, and Brief-Balance Evaluation Systems Tests, respectively.CONCLUSIONS:The BESTest and its abbreviated versions had high test-retest reliability. The MDC values of the BESTest could enable clinicians and researchers to interpret changes in the balance of patients with SCA more precisely.

RELIABILITY AND MINIMAL DETECTABLE CHANGE OF THE UPPER QUARTER Y-BALANCE TEST IN HEALTHY ADOLESCENTS AGED 12 TO 17 YEARS

There are a few studies investigating the reproducibility of the Upper Quarter Y Balance Test (YBT-UQ) in adults. However, no study has determined test-retest reliability and the minimal detectable change of the YBT-UQ in adolescents from different age cohorts. The aim of the present study was to establish test-retest reliability and minimal detectable change of the YBT-UQ in a sample of healthy adolescents. In a school setting, 111 students (59 female, 52 male) aged 12-17 years performed the YBT-UQ twice, separated by one week. Normalized maximal reach distances (% arm length) for all three directions (i.e., medial, inferolateral, superolateral) and the composite score were used as outcome measures. Intraclass correlation coefficient (ICC3,1) and standard error of measurement (SEM) were calculated to assess both relative and absolute test-retest reliability. In addition, the minimal detectable change (MDC95%), an index that is defined as the minimal amount of change in performance that falls outside the measurement error or performance changes due to variability was determined. Irrespective of age cohort, reach arm, and reach direction, the measure of relative reliability ranged from "moderate-to-good" to "excellent" ICC values and the proxy of absolute reliability was rather small (i.e., SEM ≤ 7.6%). The MDC95% needed to identify relevant effects in repeated measurements of the YBT-UQ performance ranged between 4.8% and 21.1%, depending on age, reach arm, and reach direction. The detected values imply that the YBT-UQ is a reliable field test that can be used to detect changes of upper quarter mobility/stability in healthy adolescents aged 12-17 years. 2b.

Repeatability and reproducibility of retinal and choroidal thickness measurements in Diabetic Macular Edema using Swept-source Optical Coherence Tomography.

PurposeTo evaluate the repeatability and reproducibility of retinal and choroidal thickness measured with Swept source Optical Coherence Tomography (SS-OCT) in eyes with Diabetic Macular Edema (DME).Methods42 DME eyes were imaged using SS-OCT standard Macular scanning protocols. Retinal and choroidal thickness were measured in the Total macular circle (TMC) and foveal central subfield (FCS) using device-integrated specific software. The coefficient of repeatability (CR) and intraclass correlation coefficient (ICC) were determined as a measure of repeatability and relative reliability within graders. Reproducibility was assessed using Bland-Altman plots and 95% limits of agreement (LoA) were determined as a measure of interobserver variability.ResultsIntragrader CR of retinal and choroidal thickness were 8.37 and 12.20 microns for TMC and 22.24 and 32.40 microns for FCS, and intergrader 95% LoA were 7.37–8.69 and -27.2–27.71 microns for TMC and -34.21–41.93 and -30.46–24.84 for FCS, respectively. Retinal and choroidal thickness showed very good intraobserver reliability for both TMC and FCS (ICC 0.99, LoA 0.98–0.99 in all cases). Intraobserver and interobserver variability for retinal and choroidal thickness was not significantly different for TMC (p = 0.98 and p = 0.90, p = 0.98 and p = 0.91) or FCS (p = 0.97 and p = 0.85, p = 0.78 and p = 0.73), respectively.ConclusionsRetinal and choroidal thickness in DME eyes can be quantified with good reliability, repeatability and reproducibility using new OCT devices that incorporate swept source technology. The technical advantages of this technology may provide new insights in the understanding of the choroidal changes related with DME.

(203) - Within session reliability of conditioned pain modulation in young healthy adults depends on location of test stimulus

The aim of this repeatability study was to investigate the between and within session reliability of conditioned pain modulation (CPM) in young healthy individuals. Thirty subjects (19.3 ± 1.5 years; 15 females) participated in two randomized sessions separated by approximately one week. During each session, pressure pain thresholds (PPTs) at the right quadriceps and upper trapezius muscles were assessed before and during ice water immersion (left foot, 0 ± 1°C, 105 ± 18 seconds). In one of the sessions, the CPM protocol was repeated following 23 minute quiet rest. Percentage change in CPM within and between sessions at each assessment site were compared with repeated measures ANOVAs. Intraclass correlations (ICCs (3,k)) with 95% confidence interval (CI) as a measure of relative reliability were computed within and between sessions for each assessment site. During submersion of foot in the ice water bath, participants reported moderate-to-severe peak pain intensity (6.6 ± 1.8 using 0/10 Numerical Rating Scale). Peak pain intensity decreased significantly between sessions (7.0 ± 1.0 to 6.4 ± 1.7; P = .01) but was similar within session (P > .05). PPTs significantly increased during cold pressor tests compared to baseline without ice (P < .001). The CPM response decreased at the quadriceps and upper trapezius muscles similarly following quiet rest compared with before quiet rest (trial: P < .05; trial x site: P > .05). Despite the decrease, CPM had a fair-to-good within session reliability; although this differed based on the location of the test stimulus (ICCs: quadriceps = .707 [.395–.859]; upper trapezius = .433 [−.190–.730]). Between-session reliability was poor at both assessment sites (ICCs: quadriceps = .208 [−.715–.628]; upper trapezius = .350 [−.401–.694]). These results suggest that CPM is not fully restored following a 23-minute washout period and reliability of CPM may change depending on location of the test stimulus. Future studies are needed to investigate the factors involved in CPM reliability.

Multi-scenario optimization approach for assessing the impacts of advanced traffic information under realistic stochastic capacity distributions

In this study, to incorporate realistic discrete stochastic capacity distribution over a large number of sampling days or scenarios (say 30–100days), we propose a multi-scenario based optimization model with different types of traveler knowledge in an advanced traveler information provision environment. The proposed method categorizes commuters into two classes: (1) those with access to perfect traffic information every day, and (2) those with knowledge of the expected traffic conditions (and related reliability measure) across a large number of different sampling days. Using a gap function framework or describing the mixed user equilibrium under different information availability over a long-term steady state, a nonlinear programming model is formulated to describe the route choice behavior of the perfect information (PI) and expected travel time (ETT) user classes under stochastic day-dependent travel time. Driven by a computationally efficient algorithm suitable for large-scale networks, the model was implemented in a standard optimization solver and an open-source simulation package and further applied to medium-scale networks to examine the effectiveness of dynamic traveler information under realistic stochastic capacity conditions.

Assessment of inter-rater variability of the Senior Fitness Test in the geriatric population: A community based study

Background: Maintenance of physical activity is of paramount importance in geriatric care and it is imperative to be able to objectively assess physical activity level in the geriatric population. However, majority of the established assessment protocols are designed for relatively younger adults, and are not validated for the elderly. The Senior Fitness Test (SFT) is aimed at assessing the underlying functional fitness for older adults. Methods: A community based prospective study to assess the test-retest reliability of SFT in elderly subjects, aged 65 – 75 years. Subjects with any acute illnesses, acute musculoskeletal injury, hypertension, and with visual problems hampering test performance were excluded. The study was conducted by two observers on two days at the subject’s own locality. The Intraclass Correlation Coefficient (ICC) with 95% confidence intervals (CIs) was used as a measure of relative reliability. The standard error of measurement and minimal detectable change (MDC) were used to measure absolute reliability. Results: Thirty one participants (mean age- 68.32±2.58 years) were assessed. The ICC reflected high reliability (0.934–0.994) in all SFT items. MDC values (90% CI) for various SFT were as follows: chair sit and reach test = 1.55, back scratch test = 1.41, 30 second chair stand test = 1.15, 30-second arm curl test = 2.53, 8 foot up-and-go test = 1.47 and 2-minute step test = 1.40. Bland–Altman plots for all the tests were positively skewed and heteroscedastic. Conclusion: The SFT showed high test–retest reliability and thus is suitable for evaluating physical fitness in elderly and can be utilized in larger studies for the geriatric population.

Reliability of the Senior Fitness Test in Community‐dwelling Older People with Cognitive Impairment

In older people with cognitive impairment, we require reliable and valid measures to assess physical fitness and to measure change, for example, as a result of an exercise intervention. The purpose of our study was to determine the relative and absolute test-retest reliability of the Senior Fitness Test (SFT) in older people with cognitive impairment. A test-retest reliability study was conducted for the Senior Fitness Test in older people with cognitive impairment. Participants were tested at two time points with a time interval of 24 hours to 1 week between tests. The Intraclass Correlation Coefficient model 3.1 (ICC, 3.1) with 95% confidence intervals (CIs) was used as a measure of relative reliability. The standard error of measurement and minimal detectable change (MDC) were used to measure absolute reliability. The ICC reflected very high reliability (0.93-0.98) in all SFT items, indicating that there was no systematic error in the measurements. MDC values at the 90% CIs were calculated: chair stand test = 2.0 repetitions, armcurl test = 2.3 repetitions, chair sit and reach test = 6.0 cm, back scratch test = 4.6 cm, 2.45-m up-and-go test = 1.4 seconds and 6-minute walk test = 37.1 metres. The SFT battery showed high to very high test-retest reliability and thus may be suitable for detecting changes in physical fitness and evaluating physical fitness in older people with cognitive impairment, both in research and for clinical purposes.

Repeatability and Reproducibility of Choroidal Vessel Layer Measurements in Diabetic Retinopathy Using Enhanced Depth Optical Coherence Tomography

To describe novel segmentation protocols for choroidal layers, Sattler's medium and Haller's large vessel layers, using enhanced depth imaging optical coherence tomography (EDI-OCT), and to examine the repeatability and reproducibility of these measurements in eyes with diabetic retinopathy. Fifty-one patients with Type 2 diabetes mellitus were imaged using custom EDI scanning protocols. Detailed segmentation was performed to quantify the retina, choroid, Haller's large, and Sattler's medium vessel layers in the total macular circle (TMC) and foveal central subfield (FCS). The coefficient of repeatability (CR) and intraclass correlation coefficient (ICC) were used as a measure of repeatability and relative reliability within graders. Reproducibility or interobserver variability was assessed using Bland-Altman plots and 95% limits of agreement (LoA). Intragrader CR of the retina, choroid, Sattler's, and Haller's layers for thickness measurements were 19.2, 26.9, 35.2, and 29.2 μm, respectively. Intergrader 95% LoA were 27.9, 41.5, 38.6, 31.1 μm (thickness), respectively. Choroidal sublayer measurements showed good intraobserver reliability (ICC 0.78-0.98). Interobserver variability for retinal and choroidal measurements was not significantly different (P > 0.45). Measurements from the TMC showed slightly better repeatability and agreement compared with the FCS alone. Mean intergrader differences were reduced after training, and were most apparent in choroidal sublayers. The choroidal vascular sublayers can be quantified with good reliability, repeatability, and reproducibility. Accurate quantitative assessment of these sublayers may provide new insights into the role of the choroid in visual loss in patients with diabetic retinopathy, and prove useful for future clinical trials.

EXPONENTIAL DOMINANCE AND UNCERTAINTY FOR WEIGHTED RESIDUAL LIFE MEASURES

In this article notions of exponential dominance and uncertainty for weighted and unweighted distributions are explored and used to compare values of the informational energy function and the differential entropy. Stochastic inequalities and bounds for cross-discrimination and uncertainty measures in weighted and unweighted residual life distribution functions and related reliability measures are presented. Moment-type inequalities for the comparisons of weighted and unweighted residual life distributions are also presented.

Reliability of Kinematic and Kinetic Measures of Jump Performance Using Accelerometry

PURPOSE: The purpose of this study was to determine the reliability of kinetic and kinematic variables measured from bilateral and unilateral countermovement and drop jumps using an accelerometer. METHODS: Twenty six subjects with mean age, height, and weight of 21 ± 1.2 years, 179.3 ± 9.9 cm, and 82.18 ± 16.2 kg, respectively completed the study. After a 5-minute warm up and dynamic stretches, the following jumps were completed in random order with a 30-second rest period between each trial: bilateral countermovement vertical jump (BCV), bilateral countermovement horizontal jump (BCH), bilateral 40 cm drop vertical jump (BDV), bilateral 40 cm drop horizontal jump (BDH), unilateral countermovement vertical jump (UCV), unilateral countermovement horizontal jump (UCH), unilateral 20 cm drop vertical jump (UDV), and unilateral 20 cm drop horizontal jump (UDH). An accelerometer (Inform Sport Training Systems, Victoria, BC. Canada), worn at the waist, measured the following jump kinematics: jump height, ground contact time, concentric time, time to peak concentric force, time to peak power, and reactive strength (jump height divided by ground contact time). Kinetic measures included mean concentric force, peak concentric force, and peak power. Jump distance during the horizontal jumps was measured using a tape measure. After completing all jumps in one session, a minimum of 48 hours of rest was allowed before repeating the jumps in a second session. The best of 3 trials was recorded for analysis. The ground contact recorded for analysis was taken from the highest reactive strength found during the drop jumps. The Pearson r was used as a measure of relative reliability (between-subject variation) and the coefficient of variation (cv), expressed as a percent, determined absolute reliability (within-subject variation) after test-retest procedures. RESULTS: Relative reliability was high ( 0.69 ≤ r ≤ 0.93) for all of the bilateral vertical jump variables while jump height, mean concentric force, and peak concentric force during the BCV and jump height during BDV was found to produce moderate to high absolute reliability with a range between 3.7–9.4%. Relative reliability ranged from moderate to high ( 0.5 ≤ r ≤ 0.96) for the unilateral vertical jump variables while the CV for jump height (8.3%) and peak concentric force (9.2%) during the UCV demonstrated moderate absolute reliability. High relative (r = 0.96 and 0.94) and absolute reliability (cv = 3.3 and 4.4%) was found for jump distance during the BCH and BDH, respectively while reactive strength during the BDH produced moderate relative (r = 0.67) and low absolute (cv = 15.3%) reliability. Similar results were found for the unilateral horizontal jumps. Jump distance demonstrated high relative (r = 0.91 and 0.91) and absolute (cv = 4.8 and 6.3%) reliability during the UCH and UDH, respectively while reactive strength during the UDH demonstrated moderate (r = 0.62) and low (cv = 19%) reliability. Conclusion: The best overall reliable measures were jump height and distance while reactive strength demonstrated moderate to low reliability. All other variables, except for ground time during the unilateral jumps, produced high and significant relative reliability but low absolute reliability. Practical Application: The data indicate that the variables can be used to rank subjects but, beside jump height and distance, do not provide enough within-subject accuracy to monitor improvement.

Bagging for path-based clustering

A resampling scheme for clustering with similarity to bootstrap aggregation (bagging) is presented. Bagging is used to improve the quality of path-based clustering, a data clustering method that can extract elongated structures from data in a noise robust way. The results of an agglomerative optimization method are influenced by small fluctuations of the input data. To increase the reliability of clustering solutions, a stochastic resampling method is developed to infer consensus clusters. A related reliability measure allows us to estimate the number of clusters, based on the stability of an optimized cluster solution under resampling. The quality of path-based clustering with resampling is evaluated on a large image data set of human segmentations.

Inequalities and bounds for kernel length-biased density estimation

In this note non-parametric estimates of the length-biased probability density function and related reliability measures are presented. Non-parametric estimates are also presented under random censoring. Inequalities and bounds for the error of kernel estimators used for the estimation of length-biased probability densities are obtained. Non-asymptotic bounds and stochastic convergence results are established. Inference for length-biased energy functions is developed and implemented.

Cost related reliability measures for power system equipment

Cost considerations play a very important role in power system operation and planning. In traditional reliability analysis, these costs have rarely been taken into account, primarily because of the lack of suitable mathematical models. The aim of this paper is to introduce one set of such models. To model the economic aspects of component on system reliability, cost rates are introduced to the states and cost impulses to the transitions of the Markov chain. Then, the cost related reliability measures are defined and their relationship to the traditional reliability indices is illustrated. A brief discussion on the solution procedures for the modified Markov chain is offered followed by an illustrative numerical example.

A capacity related reliability for transportation networks

AbstractA capacity related reliability for transportation networks with random link capacity is introduced. It is defined as the probability that the road network can accommodate a certain level of traffic demand, and is built on the concept of network reserve capacity. Network reserve capacity is defined as the largest multiplier applied to an existing origin‐destination demand matrix that can be allocated to a transportation network in a user‐optimal way without violating the link capacities. Due to large variability associated with link capacities, a probabilistic approach is adopted to model the different physical and operational factors that often degrade the capacity of roadways. A Monte Carlo simulation procedure is developed to estimate the capacity related reliability measure. Numerical results are provided to demonstrate the feasibility of the approach.

RELIABILITY ANALYSIS OF PHASED MISSIONS

It is shown that in a number of cases mission success probabilities and related reliability measures can be determined, once appropriate mission phases are defined. The results are general, i.e., not limited to the Markov model case, but intentionally kept “simple” by considering only few components and few different phases. The problems specifically addressed (and solved) are: (1) Non-ideal switches for activating spares, (2) and (3) degraded operation, and change from TMR (Triple Modular Redundancy) to simplex structure on the first component failure, respectively, (4) preventive renewals after alternating periods, and (5) load-dependent two-phased life time distribution.

Reliability modelling for some computer systems

This paper investigates two mathematical models based on structural computer systems. There are two types of operating environment in computer namely DOS and UNIX. Central Processing Unit (CPU) is the brain of the computer and it guides the monitor and dumb terminal (DT) according to the sequence of instructions as given by operator. A sensitive volume due to micro-chips, exists in the computer. An electromagnetic interfrence with this sensitive volume changes the operating behaviour of computer. These changes generate the partial and complete failure states. Several cost related reliability measures of the system effectiveness are studied by using the regenerative point technique.

Analyzing the effect of permanent, intermittent and transient faults on a gracefully degrading microcomputer

In this paper investigations into the effect of permanent, intermittent and transient faults on a gracefully degrading microcomputer are reported. Two discrete-state continuous time Markov chains are used in order to model the fault/error handling and the fault occurence repair processes. The models are separately solved with the aid of decomposition/aggregation technique. A numerical algorithm is also used in order to evaluate performability of the microcomputer. Finally, the influence of permanent, intermittent and transient faults on this performance related reliability measure are analyzed.

A perfomability approach to the cost minimization of a class of gracefully degrading computer systems

Parallel processing systems offer both higher performance and enhanced reliability, in comparison with classical, sequential machines. This work is focused on the cost minimization of a restricted class of gracefully degrading systems: the homogeneous (i.e. built up by means of identical modules), triple-bus architecture based multi-microcomputer systems. We use performability as a performance related reliability measure and define a specific optimization problem which aims to the cost minimization. Its decision variable are the number of system constituent microcomputers and their failure rate. In order to solve this problem we developed a heuristic searching algorithm. It is applied in the case of a practical design example.

Evaluation of Importance and Related Reliability Measures for Electric Power Systems

Evaluation of Importance and Related Reliability Measures for Electric Power Systems