Coefficient Of Variation For Time Research Articles

Conventional methods to prescribe exercise intensity are ineffective for exhaustive interval training

PurposeTo compare methods of relative intensity prescription for their ability to normalise performance (i.e., time to exhaustion), physiological, and perceptual responses to high-intensity interval training (HIIT) between individuals.MethodsSixteen male and two female cyclists (age: 38 ± 11 years, height: 177 ± 7 cm, body mass: 71.6 ± 7.9 kg, maximal oxygen uptake ( dot{text{V}} O2max): 54.3 ± 8.9 ml·kg−1 min−1) initially undertook an incremental test to exhaustion, a 3 min all-out test, and a 20 min time-trial to determine prescription benchmarks. Then, four HIIT sessions (4 min on, 2 min off) were each performed to exhaustion at: the work rate associated with the gas exchange threshold ( dot{text{W}} GET) plus 70% of the difference between dot{text{W}} GET and the work rate associated with dot{text{V}} O2max; 85% of the maximal work rate of the incremental test (85% dot{text{W}} max); 120% of the mean work rate of the 20 min time-trial (120%TT); and the work rate predicted to expend, in 4 min, 80% of the work capacity above critical power. Acute HIIT responses were modelled with participant as a random effect to provide estimates of inter-individual variability.ResultsFor all dependent variables, the magnitude of inter-individual variability was high, and confidence intervals overlapped substantially, indicating that the relative intensity normalisation methods were similarly poor. Inter-individual coefficients of variation for time to exhaustion varied from 44.2% (85% dot{text{W}} max) to 59.1% (120%TT), making it difficult to predict acute HIIT responses for an individual.ConclusionThe present study suggests that the methods of intensity prescription investigated do not normalise acute responses to HIIT between individuals.

Retroperitoneoscopic Pyeloplasty for Ureteropelvic Junction Obstruction in Children: Value of Robotic Assistance

AimRetroperitoneal pyeloplasty (RP) for pediatric ureteropelvic junction obstruction (UPJO) performed using retroperitoneoscopy (retro-RP) or robotic assistance (robo-RP) were compared. MethodsAll subjects were Japanese, matched for age, weight, and RP diameters. All RP were performed in the lateral decubitus position at a single institute by the same team using identical protocols. Five independent surgeons were asked to score intraoperative video recordings for perceived difficulty of suturing (DOS; 5 = impossible; 4 = difficult; 3 = tedious; 2 = slow; 1 = easy) and rank RP as +1 if robo-RP appeared to be superior, 0 if they appeared to be the same, and −1 if robo-RP appeared to be inferior. ResultsRobo-RP performed 2018-2022 (n = 22) were matched with retro-RP performed 2011-2019 (n = 34). Mean overall operative times were similar (robo-RP: 305.2 ± 57.8 min versus retro-RP: 340.0 ± 117.9 min; p = 0.19), but securing the larger retroperitoneal space required for robo-RP took significantly longer; 50.8 ± 13.9 min versus 24.3 ± 9.6 min; p < 0.0001. Total anastomotic time (TAT) and TAT per suture were both significantly shorter for robo-RP (p < 0.0001). The coefficient of variation for time taken to place one suture was smaller for robo-RP than for retro-RP. DOS was lower for robo-RP with less variance (p < 0.01). Robo-RP had shorter drainage tube insertion, ambulated quicker postoperatively, and shorter hospitalization. Retro-RP had anastomotic complications; leaks (n = 2) and strictures (n = 2, requiring conventional open re-pyeloplasty). Robo-RP had no anastomotic complications and was ranked +1 unanimously. ConclusionsThe RP anastomosis was quicker with less complications and more precise with robotic assistance in matched patients under similar circumstances. Should RP be indicated, robo-RP is recommended. Level of evidenceIII.

Increased Intra-Individual Variability as a Marker of Executive Dysfunction in Generalized Anxiety Disorder

Recent studies suggest that individual difference in intra-individual variability (IIV) of reaction times is an important indicator of attentional executive control. However, there are few existing studies on the executive control of high trait-anxious individuals assessed by using reaction time variability. This study assessed whether executive functions are impaired among clinical and non-clinical trait-anxious individuals indicated by IIV. The cross-reliability and discriminative power of three IIV parameters (raw intra-individual standard deviation, SD; reaction time coefficient of variation, RTCV; and mean absolute deviation, MAD) were compared. Twenty-five non-clinical individuals with low trait anxiety (LTA), 31 non-clinical individuals with high trait anxiety (HTA), and 19 clinical patients diagnosed with generalized anxiety disorder (GAD) finished self-reported measures, an emotional spatial-cuing task, and a non-emotional arrow flanker task. In the emotional task, GAD patients had significantly slower response speed, lower accuracy, and greater IIV parameters than the LTA and HTA groups. In the non-emotional task, the GAD group exhibited poorer processing efficiency, greater SD and RTCV, and intact performance effectiveness. RTCV is suggested to be a better marker of executive dysfunction than SD and MAD due to its good discriminative power and reliability as well as less affected by reaction times.

Impact of the dedicated infrastructure on bus service quality: an empirical analysis

ABSTRACTAn econometric analysis is conducted to quantify the impact of different variables on the service quality of the Santiago, Chile bus system. The indicators tested as measures of service quality are the average bus speed, the bus trip time coefficient of variation and the bus headway coefficient of variation. The analysis uses peak hour data obtained for all the routes served by the system’s various concessionaire operators. A separate multiple linear regression model is estimated for each indicator, with the latter as the explained variable. The main explanatory variables are a series of design factors representing different types of dedicated route infrastructure and the incorporation in some routes of segments of urban motorway. The results of the models show that the existence of dedicated bus route infrastructure positively impacts all three service quality indicators. The use of motorway segments in particular has a major positive effect on average speed. The model estimates also reveal that the main explanatory factor in headway variability at the end of a route is the headway variability at the start of it, the latter factor determined by operator management decisions regarding bus despatches.

Simulation-based pricing optimization for improving network-wide travel time reliability

ABSTRACTTravel time variability in a network is an important measure of the transportation system performance and a major factor influencing the decision-making of system management such as congestion pricing. The congestion-pricing problem with reliability maximization as the goal of a transportation network is characterized by expensive-to-evaluate objective functions without closed forms. In this paper, an effective simulation-based optimization (SBO) method is utilized to solve the problem. The network reliability is measured by a weighted average link travel time coefficient of variation (CV) with link traffic flows as the weights. We employ DynusT to evaluate the system reliability as the objective function corresponding to different toll charges for a new toll road in Maryland. The results show that the two optimal toll charge strategies improve the network-wide reliability, reducing the weighted travel time CV by 9.60% and 1.16%, respectively, when compared to the baseline toll.

Improving the logistics of a constant order-cycle kanban system

Kanban systems are simple, effective means of improving production that are widely applied in practice. Based on the logistic process involved, kanban systems can be divided into constant order-quantity and constant order-cycle systems. The former has received much research attention, but the latter, also known as a milk run, has been relatively neglected. Further, most prior work has been based on deterministic data, which is an assumption often violated in practice. We present the case of a manufacturer of domestic water heating equipment where a constant order-cycle kanban implementation initially failed. A structured Define–Measure–Analyse–Improve–Control approach is adopted to improve the process. It was revealed that the failure was due to high variability in the logistic processes involved. Decreasing this variability resulted in a reduction of tardy replenishment routes from 50 to 3%; a reduction in the route time coefficient of variation from 40 to 16%; and a reduction in the mean route time from 31 to 25 min. These improvements allowed one of three existing routes to be eliminated without any negative impact on replenishment. This led to financial savings through the elimination of two operators. The logistic process appears to have a significant impact on kanban performance. Consequently, kanban implementations should not only focus on the kanban system itself but also on the other processes involved. Future research should therefore explore how resources can best be allocated between the different aspects required for a successful kanban implementation.

Effect of Statistical Scatter of Spinneret Diameter on the Dynamics of Formation and Uniformity of Elementary Filaments

The method of statistical modeling is used to determine the relationship between the thickness of filaments and the coefficients of variation for time and density. It is shown that the standard deviation of the outgoing flow is directly proportional to these coefficients individually and in combination. The mathematical model which was constructed allows these relationships to be used to design new systems for controlling the passage of a polymer solution through a spinneret.

Mutation Induced Extinction in Finite Populations: Lethal Mutagenesis and Lethal Isolation

Reproduction is inherently risky, in part because genomic replication can introduce new mutations that are usually deleterious toward fitness. This risk is especially severe for organisms whose genomes replicate “semi-conservatively,” e.g. viruses and bacteria, where no master copy of the genome is preserved. Lethal mutagenesis refers to extinction of populations due to an unbearably high mutation rate (U), and is important both theoretically and clinically, where drugs can extinguish pathogens by increasing their mutation rate. Previous theoretical models of lethal mutagenesis assume infinite population size (N). However, in addition to high U, small N can accelerate extinction by strengthening genetic drift and relaxing selection. Here, we examine how the time until extinction depends jointly on N and U. We first analytically compute the mean time until extinction (τ) in a simplistic model where all mutations are either lethal or neutral. The solution motivates the definition of two distinct regimes: a survival phase and an extinction phase, which differ dramatically in both how τ scales with N and in the coefficient of variation in time until extinction. Next, we perform stochastic population-genetics simulations on a realistic fitness landscape that both (i) features an epistatic distribution of fitness effects that agrees with experimental data on viruses and (ii) is based on the biophysics of protein folding. More specifically, we assume that mutations inflict fitness penalties proportional to the extent that they unfold proteins. We find that decreasing N can cause phase transition-like behavior from survival to extinction, which motivates the concept of “lethal isolation.” Furthermore, we find that lethal mutagenesis and lethal isolation interact synergistically, which may have clinical implications for treating infections. Broadly, we conclude that stably folded proteins are only possible in ecological settings that support sufficiently large populations.

Network Stratification Method by Travel Time Variation

There is a need for fair and statistically valid assessments of traveler information data services. For measurement of the accuracy of a traveler information service, ground truth data must be collected and compared with the data service being evaluated. Past assessments of data quality have typically used floating-car runs or travel time estimates derived from loop detector speed data to determine ground truth benchmarks. Newer approaches such as measurement of travel time from Bluetooth samples can provide statistically valid sample sizes. However, determining the minimum sample size before data collection is critical to minimize data collection costs and maximize accuracy of ground truth data. An analysis of travel time data from Houston, Texas, is presented. The distribution of travel time variance is explored and a method for network stratification with a classification model is developed. The method can be applied to classify freeway links based on the travel time coefficient of variation. The method will help engineers in determining which links in a network to test and in estimating the minimum sample size per link.

Optimal allocation of servers and processing time in a load balancing system

We consider the problem of allocating processing time in a multi-channel load balancing system by focusing on systems where processing times have distributions characterized by high variability. Our objective is to reduce congestion by routing jobs to servers based on their workload. Specifically, we arrange servers in two stations in series, and require that the load be balanced between the two stations. All arrivals join the first service center where they receive a maximum of T units of service. Arrivals with service requirements that exceed the value T join the second station where they receive their remaining service. For a variety of heavy tail service time distributions, characterized by high variability, analytical and numerical comparisons show that our scheme provides better system performance than the standard parallel multi-server model in the sense of reducing the mean delay per customer when the traffic intensity is not too low. In particular, we develop lower bounds on the traffic intensity and the service time coefficient of variation beyond which the balanced series system outperforms the parallel system.

The performance of unpaced production lines with unequal operating time variabilities and buffer sizes

This paper investigates the behaviour of unpaced production lines that are imbalanced with respect to both their work time coefficients of variation and buffer sizes. The lines were simulated with varied values of line length, buffer capacity and patterns of imbalance. Using a range of statistical methods, idle time and average buffer level (ABL) output data were analysed and compared to a balanced line counterpart. Various conclusions concerning the relationships among the exogenous and endogenous variables were made. The best pattern in terms of idle time was identified to be a bowl-shaped coefficient of variation configuration, combined with a buffer arrangement whereby more buffer capacity is concentrated at the beginning of the line. In terms of ABL, the superior pattern turned out to be a bowl-shaped coefficient of variation order, together with a buffer arrangement under which the buffers are concentrated towards the end of the line.

Comparison of Left Ventricular Dyssynchrony by Two-Dimensional Speckle Tracking Versus Tissue Doppler Imaging in Patients With Non–ST-Elevation Myocardial Infarction and Preserved Left Ventricular Systolic Function

Assessment of left ventricular (LV) dyssynchrony after myocardial infarction has prognostic value. There were no reference ranges for 2-dimensional (2D) speckle tracking synchrony, and it was unclear whether color tissue Doppler imaging and 2D speckle tracking synchrony indexes were comparable. One hundred twenty-two healthy volunteers and 40 patients with non-ST-elevation myocardial infarction (NSTEMI) had LV systolic and diastolic synchrony, defined as the SD of time to peak systolic (2D-SDTs) and early diastolic (2D-SDTe) velocities in the 12 basal and mid segments using 2D speckle tracking, respectively. Mean 2D-SDTs and 2D-SDTe were 29.4 +/- 16.1 and 14.2 +/- 6.1 ms in healthy subjects, respectively. Gender and mean 2D systolic velocity independently predicted 2D-SDTs, and mean 2D early diastolic velocity independently predicted 2D-SDTe. Bland-Altman analysis showed suboptimal agreement between 2D speckle tracking and tissue Doppler imaging dyssynchrony indexes. 2D speckle tracking showed lower coefficients of variation for time to peak systolic and early diastolic velocities than tissue Doppler imaging. There were no significant differences in coefficients of variation for 2D speckle tracking systolic and diastolic synchrony for high versus low frame rates. Patients with NSTEMI had significantly lower ejection fraction, but higher LV mass and wall stress than healthy subjects. Only 2D-SDTs was significantly higher in patients with NSTEMI compared with healthy subjects (37.1 +/- 22.5 vs 29.4 +/- 16.1 ms; p = 0.02). In conclusion, 2D-SDTs was gender specific and influenced by global systolic function, and 2D-SDTe was influenced by global diastolic function. 2D speckle tracking and tissue Doppler imaging dyssynchrony indexes were not comparable. 2D speckle tracking may be a more sensitive discriminator of LV systolic dyssynchrony than tissue Doppler imaging.

Assessment of metabolite quantitation reproducibility in serial 3D‐1H‐MR spectroscopic imaging of human brain using stereotactic repositioning

Intrasubject reproducibility of metabolite quantitation in three-dimensional proton magnetic resonance spectroscopic imaging (3D-MRSI) was investigated in 10 healthy volunteers over five separate sessions using two echo times (TEs): 144 and 30 ms. The use of a Gill-Thomas-Cosman (GTC) stereotactic head frame enabled precise subject repositioning and immobilization. Metabolite levels from each voxel in the volume of interest (VOI) were quantified using the Linear Combination of Model spectra (LCModel) analysis algorithm, and coefficients of variation (CVs) were calculated. Standard error estimates (%SD or Cramer-Rao lower bounds) generated by LCModel were used as a confidence filter. The 95% confidence interval (CI) was found for each metabolite, providing an indication of the normal fluctuation expected for 3D-MRSI. In vivo, median CVs at the %SD < or = 20 level were found to be (%CV for TE = 144 and 30 ms, respectively): N-acetyl-aspartate plus N-acetyl-aspartyl-glutamate (NAA): 10.2% and 13.5%; creatine plus phosphocreatine (Cr), 14.4% and 21.7%; and choline-containing compounds (Cho), 15.2% and 18.4%. Relaxing the statistical filtering criteria to %SD < or = 30 increased median CVs by less than 5% and permitted in vivo quantitation reproducibility to be evaluated for glutamine plus glutamate (Glx) and myoinositol (Ins) for TE = 30 ms, yielding CVs of 24.0% and 21.0%, respectively.

ENVIRONMENTAL AND GENETIC SOURCES OF DIVERSIFICATION IN THE TIMING OF SEED GERMINATION: IMPLICATIONS FOR THE EVOLUTION OF BET HEDGING

Environmental variation that is not predictably related to cues is expected to drive the evolution of bet-hedging strategies. The high variance observed in the timing of seed germination has led to it being the most cited diversification strategy in the theoretical bet-hedging literature. Despite this theoretical focus, virtually nothing is known about the mechanisms responsible for the generation of individual-level diversification. Here we report analyses of sources of variation in timing of germination within seasons, germination fraction over two generations and three sequential seasons, and the genetic correlation structure of these traits using almost 10,000 seeds from more than 100 genotypes of the monocarpic perennial Lobelia inflata. Microenvironmental analysis of time to germination suggests that extreme sensitivity to environmental gradients, or microplasticity, even within a homogeneous growth chamber, may act as an effective individual-level diversification mechanism and explains more than 30% of variance in time to germination. The heritability of within-season timing of germination was low (h(2) = 0.07) but significant under homogeneous conditions. Consistent with individual-level diversification, this low h(2) was attributable not to low additive genetic variance, but to an unusually high coefficient of residual variation in time to germination. Despite high power to detect additive genetic variance in within-season diversification, it was low and indistinguishable from zero. Restricted maximum likelihood detected significant genetic variation for germination fraction (h(2) = 0.18) under homogeneous conditions. Unexpectedly, this heritability was positive when measured within a generation by sibling analysis and negative when measured across generations by offspring-on-parent regression. The consistency of dormancy fraction over multiple delays, a major premise of Cohen's classic model, was supported by a strong genetic correlation (r = 0.468) observed for a cohort's germination fraction over two seasons. We discuss implications of the results for the evolution of bet hedging and highlight the need for further empirical study of the causal components of diversification.

Reproducibility in simulated 40 km time trial cycling and its associated metabolic stress

This study examined the reproducibility of a simulated 40 km time trial (40TT) repeated on 3 separate occasions prior to pre‐season training. On days 1 (TT1), 3 (TT2) and 5 (TT3), 9 experienced cyclists (X± SD VO2max: 4.27 ± 0.28 L · min−1) performed the 40TT using their own bicycles mounted on wind‐loaded rollers which were mechanically connected to an odometer to record distance cycled. Exercise time and selected metabolic and respiratory measures were recorded at 10 km intervals. The results showed that the mean VO2 (3.57 ±0.50, 3.61 ±0.38, 3.59±0.38L· min−1), cycling velocity (557.4±42.7, 568.3±46.1, 579.8±36.7 m·min−1) and time (min: s; 72:00 ± 5 :20, 70: 50 ± 5:16, 69: 57 ± 4:49) were not different (p < 0.05) between TT1, TT2, TT3, respectively. However, coefficient of variation for time was 3.7%. 40TT cycling intensity was performed at 7% above ventilation threshold of each individual. BLa (mM) was different at only the 10 km interval between TT1 (6.2 ±1.98) vs. TT2 (4.3 ±1.41) and TT3 (4.5 ± 1.63), suggesting that the subjects began TT1 at a higher intensity but were not able to maintain the pace. The intra‐class coefficient ranged between 0.36 and 0.91 for selected variables. The poorest relationship for each was between TT1 vs. TT2 and TT1 vs. TT3. These results suggest that a simulated 40TT adequately assessed the metabolic stress of the cyclists, but that the first attempt was not a valid measure of each subject's performance ability. A learning trial seems important even when assessing experienced, competitive cyclists, prior to pre‐season training.

A simple spreadsheet approach to understanding work flow in production facilities

This paper looks at how queuing decomposition models, developed using spreadsheet software, can be used to obtain insight into work flow behaviour within a production facility. Relationships appropriate to model flow lines and job shops are developed. The approach proves valuable in helping to understand variance and covariance effects under different loading and routing assumptions. A particular benefit over the use of simulation or commercial rapid modelling software is that all relationships are transparent. This allows fundamental insights to be developed more readily. Understanding the relationships involved can help guide process design and improvement efforts. Comparisons with simulation results show that the queuing model performs well. Results are generated for the queuing model under different routing, utilization and variability assumptions. The behaviour observed is rationalized and opportunities for improvement of production systems are identified. For example, it is demonstrated that when processing time coefficients of variation are less than one, it is beneficial to have work flow that is as unidirectional as possible.

Functional tests in elderly osteoarthritic subjects: variability of performance.

The purpose of this study was to evaluate the variability of performance of timed walking and sit-to-stand tests in elderly osteoarthritic subjects. Thirteen elderly subjects were asked to walk, as quickly as possible, along a flat corridor a distance of ten metres. The time and number of strides taken were recorded. Fourteen subjects were asked to perform a series of five sit-to-stand movements as quickly as possible from a plinth 48 cm high. Subjects performed three repeats of each test procedure with a two-minute rest period between each. This was undertaken on three separate occasions within a one-week period. A significant difference (p < 0.05) was observed for the time taken to complete the ten metres over the nine tests, but no significant difference was observed in the number of strides taken. The mean coefficient of variation for time taken was 7.3 per cent, which compares favourably with normal biological systems (1). No significant difference was observed for the time taken during the sit-to-stand test over the nine tests. These simple tests of functional ability may be confidently applied as sequential measures in the clinical setting.

Technical Note—On Waiting Times for a Queue in Which Customers Require Simultaneous Service from a Random Number of Servers

We consider a queueing system, first introduced by L. Green in 1980, in which customers from a Poisson arrival stream request simultaneous service from a random number of identical servers with exponential service times. Computational formulas for the second moment of time in queue are given, along with tables of these values for selected systems. Numerical results show that the coefficient of variation for time in queue is always greater than 1 and decreases with increasing congestion.