Approximate Confidence Limits for the Coefficient of Variation of Gamma Distributions

Biometrics ◽  
1965 ◽  
Vol 21 (3) ◽  
pp. 733 ◽  
Author(s):  
H. Linhart
Keyword(s):  
Coefficient Of Variation ◽  
Confidence Limits ◽  
Gamma Distributions

Reliability and Construct Validity of Yo-Yo Tests in Untrained and Soccer-Trained Schoolgirls Aged 9–16

2016 ◽  
Vol 28 (2) ◽  
pp. 321-330 ◽  
Author(s):  
Susana C. A. Póvoas ◽  
Carlo Castagna ◽  
José Manuel da Costa Soares ◽  
Pedro Silva ◽  
Manuel Coelho-e-Silva ◽  
...  
Keyword(s):  
Heart Rate ◽  
Construct Validity ◽  
Coefficient Of Variation ◽  
Intermittent Exercise ◽  
Intraclass Correlation ◽  
Soccer Players ◽  
Confidence Limits ◽  
Peak Heart Rate ◽  
Level 1 ◽  
Level 2

Purpose:The reliability and construct validity of three age-adapted-intensity Yo-Yo tests were evaluated in untrained (n = 67) vs. soccer-trained (n = 65) 9- to 16-year-old schoolgirls.Methods:Tests were performed 7 days apart for reliability (9- to 11-year-old: Yo-Yo intermittent recovery level 1 children’s test; 12- to 13-yearold: Yo-Yo intermittent endurance level 1; and 14- to 16-year-old: Yo-Yo intermittent endurance level 2).Results:Yo-Yo distance covered was 40% (776 ± 324 vs. 556 ± 156 m), 85% (1252 ± 484 vs. 675 ± 252 m) and 138% (674 ± 336 vs. 283 ± 66 m) greater (p ≤ .010) for the soccer-trained than for the untrained girls aged 9–11, 12–13 and 14–16 years, respectively. Typical errors of measurement for Yo-Yo distance covered, expressed as a percentage of the coefficient of variation (confidence limits), were 10.1% (8.1–13.7%), 11.0% (8.6–15.4%) and 11.6% (9.2–16.1%) for soccer players, and 11.5% (9.1–15.8%), 14.1% (11.0–19.8%) and 10.6% (8.5–14.2%) for untrained girls, aged 9–11, 12–13 and 14–16, respectively. Intraclass correlation coefficient values for test-retest were excellent (0.795–0.973) in both groups. No significant differences were observed in relative exercise peak heart rate (%HRpeak) between groups during test and retest.Conclusion:The Yo-Yo tests are reliable for determining intermittent-exercise capacity and %HRpeak for soccer players and untrained 9- to 16-year-old girls. They also possess construct validity with better performances for soccer players compared with untrained age-matched girls, despite similar %HRpeak.

Interspike interval distributions of spiking neurons driven by fluctuating inputs

2011 ◽  
Vol 106 (1) ◽  
pp. 361-373 ◽  
Author(s):  
Srdjan Ostojic
Keyword(s):  
Coefficient Of Variation ◽  
Cortical Neurons ◽  
Interspike Interval ◽  
Full Range ◽  
Spiking Neurons ◽  
Neuron Models ◽  
Integrate And Fire ◽  
Gamma Distributions ◽  
Spiking Neuron Models ◽  
Analytical Tools

Interspike interval (ISI) distributions of cortical neurons exhibit a range of different shapes. Wide ISI distributions are believed to stem from a balance of excitatory and inhibitory inputs that leads to a strongly fluctuating total drive. An important question is whether the full range of experimentally observed ISI distributions can be reproduced by modulating this balance. To address this issue, we investigate the shape of the ISI distributions of spiking neuron models receiving fluctuating inputs. Using analytical tools to describe the ISI distribution of a leaky integrate-and-fire (LIF) neuron, we identify three key features: 1) the ISI distribution displays an exponential decay at long ISIs independently of the strength of the fluctuating input; 2) as the amplitude of the input fluctuations is increased, the ISI distribution evolves progressively between three types, a narrow distribution (suprathreshold input), an exponential with an effective refractory period (subthreshold but suprareset input), and a bursting exponential (subreset input); 3) the shape of the ISI distribution is approximately independent of the mean ISI and determined only by the coefficient of variation. Numerical simulations show that these features are not specific to the LIF model but are also present in the ISI distributions of the exponential integrate-and-fire model and a Hodgkin-Huxley-like model. Moreover, we observe that for a fixed mean and coefficient of variation of ISIs, the full ISI distributions of the three models are nearly identical. We conclude that the ISI distributions of spiking neurons in the presence of fluctuating inputs are well described by gamma distributions.

Validity and Reliability of GPS Units to Monitor Cricket-Specific Movement Patterns

2009 ◽  
Vol 4 (3) ◽  
pp. 381-393 ◽  
Author(s):  
Carl Petersen ◽  
David Pyne ◽  
Marc Portus ◽  
Brian Dawson
Keyword(s):  
Global Positioning System ◽  
Standard Error ◽  
Coefficient Of Variation ◽  
Movement Patterns ◽  
Positioning System ◽  
Confidence Limits ◽  
Validity And Reliability ◽  
Typical Error ◽  
Global Positioning ◽  
Further Development

Purpose:The validity and reliability of three commercial global positioning system (GPS) units (MinimaxX, Catapult, Australia; SPI-10, SPI-Pro, GPSports, Australia) were quantified.Methods:Twenty trials of cricket-specific locomotion patterns and distances (walking 8800 m, jogging 2400 m, running 1200 m, striding 600 m, sprinting 20- to 40-m intervals, and run-a-three) were compared against criterion measures (400-m athletic track, electronic timing). Validity was quantified with the standard error of the estimate (SEE) and reliability estimated using typical error expressed as a coefficient of variation.Results:The validity (mean ± 90% confidence limits) for locomotion patterns walking to striding ranged from 0.4 ± 0.1 to 3.8 ± 1.4%, whereas for sprinting distances over 20 to 40 m including run-a-three (approx. 50 m) the SEE ranged from 2.6 ± 1.0 to 23.8 ± 8.8%. The reliability (expressed as mean [90% confidence limits]) of estimating distance traveled by walking to striding ranged from 0.3 (0.2 to 0.4) to 2.9% (2.3 to 4.0). Similarly, mean reliability of estimating different sprinting distances over 20 to 40 m ranged from 2.0 (1.6 to 2.8) to 30.0% (23.2 to 43.3).Conclusions:The accuracy and bias was dependent on the GPS brand employed. Commercially available GPS units have acceptable validity and reliability for estimating longer distances (600–8800 m) in walking to striding, but require further development for shorter cricket-specifc sprinting distances.

The Development of a Custom-Built Portable Impact-testing Device for Assessing the Cushioning Properties of Athletic Socks

2013 ◽  
Vol 29 (6) ◽  
pp. 824-831 ◽  
Author(s):  
Tim Blackmore ◽  
David Jessop ◽  
Stewart Bruce-Low ◽  
Joanna Scurr
Keyword(s):  
Coefficient Of Variation ◽  
Loading Rate ◽  
Impact Force ◽  
Impact Testing ◽  
Reliability Coefficient ◽  
Systematic Bias ◽  
Testing Device ◽  
Confidence Limits ◽  
Time To Peak ◽  
Peak Impact Force

Despite manufacturer claims that athletic socks attenuate force during exercise, no device exists to assess this. Therefore, this study outlines the development of a custom-built impact-testing device for assessing the cushioning properties of socks. The device used a gravity-driven impact striker (8.5 kg), released from 0.05 m, which impacted a no-sock, sock or a basic shoe/sock condition in the vertical axis. A load cell (10,000 Hz) assessed peak impact force, time to peak impact force and loading rate. Reliability was investigated between day, between trial and within trial. Excellent reliability (coefficient of variation < 5% adjusted for 95% confidence limits) was reported for peak impact force in all conditions, with no evidence of systematic bias. Good reliability (coefficient of variation < 10% adjusted for 68% confidence limits) was reported for time to peak impact force and loading rate with some evidence of systematic bias. It was concluded that the custom-built impact-testing device was reliable and sensitive for the measurement of peak impact force on socks.

Analysis of Tritium in Water: A Collaborative Study

1969 ◽  
Vol 52 (1) ◽  
pp. 90-93
Author(s):  
Vincent J Sodd ◽  
Kenneth L Scholz
Keyword(s):  
Systematic Error ◽  
Coefficient Of Variation ◽  
Liquid Scintillation ◽  
Collaborative Study ◽  
Minimum Detectable Activity ◽  
Confidence Limits ◽  
Detectable Activity ◽  
Counting Time ◽  
Statistical Results

Abstract A liquid scintillation procedure using 1,4-dioxane, naphthalene, PPO, and POPOP as the scintillator was evaluated in a collaborative study of the determination of tritium in water. The tritium counting efficiencies for seven collaborating laboratories using this technique and commercially available liquid scintillation spectrometers ranged from 8.3 to 26.5%. The minimum detectable activity by the method, based on 99% confidence limits, 100 min counting time, and backgrounds from 9 to 67 cpm, ranged from 0.2 to 0.5 pCi/ml. Statistical results showed no evidence for systematic error. The coefficient of variation varies from 3.4 to 7.3% over the concentration range 2.91–115.8 pCi/ml. It is recommended that the method be adopted as official first action.

Interunit Reliability and Effect of Data-Processing Methods of Global Positioning Systems

2019 ◽  
Vol 14 (4) ◽  
pp. 432-438 ◽  
Author(s):  
Heidi R. Thornton ◽  
André R. Nelson ◽  
Jace A. Delaney ◽  
Fabio R. Serpiello ◽  
Grant M. Duthie
Keyword(s):  
Data Processing ◽  
Coefficient Of Variation ◽  
Effect Sizes ◽  
Confidence Limits ◽  
Range Of Movement ◽  
Processing Methods ◽  
Positioning Systems ◽  
Global Positioning ◽  
Standardized Effect Sizes ◽  
Data Processing Methods

Purpose:To establish the interunit reliability of a range of global positioning system (GPS)-derived movement indicators, to determine the variation between manufacturers, and to investigate the difference between software-derived and raw data.Methods:A range of movement variables were obtained from 27 GPS units from 3 manufacturers (GPSports EVO, 10 Hz, n = 10; STATSports Apex, 10 Hz, n = 10; and Catapult S5, 10 Hz, n = 7) that measured the same team-sport simulation session while positioned on a sled. The interunit reliability was determined using the coefficient of variation (%) and 90% confidence limits, whereas between-manufacturers comparisons and comparisons of software versus raw processed data were established using standardized effect sizes and 90% confidence limits.Results:The interunit reliability for both software and raw processed data ranged from good to poor (coefficient of variation = 0.2%; ±1.5% to 78.2%; ±1.5%), with distance, speed, and maximal speed exhibiting the best reliability. There were substantial differences between manufacturers, particularly for threshold-based acceleration and deceleration variables (effect sizes; ±90% confidence limits: −2.0; ±0.1 to 1.9; ±0.1), and there were substantial differences between data-processing methods for a range of movement indicators.Conclusions:The interunit reliability of most movement indicators was deemed as good regardless of processing method, suggesting that practitioners can have confidence within systems. Standardized data-processing methods are recommended, due to the large differences between data outputs from various manufacturer-derived software.

scholarly journals A note on the relations of certain parameters following a logarithmic transformation

1955 ◽  
Vol 34 (2) ◽  
pp. 289-296 ◽  
Author(s):  
Mary Bagenal
Keyword(s):  
Coefficient Of Variation ◽  
Biological Data ◽  
Logarithmic Transformation ◽  
Confidence Limits ◽  
Formal Relation ◽  
Log Normal ◽  
Constant Coefficient Of Variation ◽  
Log Normal Distribution ◽  
Different Sources

The logarithmic transformation has been used in the statistical analysis of certain marine biological data. Parameters calculated from the transformed distributions have been used in the description of the observations, but it appears that some of the mathematical procedures adopted have not been fully understood.Winsor & Clarke (1940) have analysed data from plankton hauls. The problem considered by them was the determination of the variability in numbers of animals caught by repeated hauls through the same body of water. The raw data were characterized by a constant coefficient of variation, i.e. the variability in catch was proportional to the size of the catch. By transformation from the actual numbers caught to their logarithmic values, it was possible to equalize the variances and to apply the method of analysis of variance to esti-mate the variability due to the different sources. Finally, an estimate of the coefficient of variation was obtained from the logarithmic values. Their method of estimation was quoted by Snedecor (1946, p. 451) and was employed by Barnes & Bagenal (1951) in their study of repeated trawl hauls. Barnes & Bagenal also calculated confidence limits for comparison of observations following the method of Silliman (1946) in his work on pilchard eggs. These methods seem to be based on a misunderstanding of the nature of a trans-formation. The formal relation between the variance of such transformed data and the coefficient of variation of the untransformed data follows from the moments of the ‘log-normal’ distribution, given first by Wicksell (1917). From these moments it will be shown that the method given by Winsor & Clarke is mathematically unsound.

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